Table of contents

The International Conference on Superconductivity and Magnetism (ICSM2008) was held at the congress centre of Ankara University in Side, Antalya, between 25–29 August 2008. The conference was the first conference on the combined fields of superconductivity and magnetism organized in Turkey at international level, and it had broad international participation from 42 countries, with registered delegates numbering over 400. A quarter of the attendees were research students. The conference attracted many of the best known leading scientists and experts in the field of superconductivity and magnetism from all over the world. The scientific program involved the presentation and discussion of 336 papers, classified as 65 invited, 81 oral and 190 posters. Submission of papers for the proceedings was on a volunteer basis and we therefore had nearly half of the presented papers, i.e. 30 submitted invited papers, peer-reviewed by Superconductor Science and Technology, and 85 submitted contributing papers, peer-reviewed by the organizers through processes administered by the Editorial Board and Scientific Committee. Reviews were conducted by expert referees at professional level and with the scientific standards expected of a proceedings journal issue published by IOP Publishing. The invited papers on superconductivity and magnetism with superconductivity were considered and processed for Superconductor Science and Technology by IOP itself. Although there are missing papers from some of the plenary speakers, we believe that this special issue of Superconductor Science and Technology (SUST) and the corresponding issue of Journal of Physics: Conference Series (JPCS) reflect most of the booming research in the fields of superconductivity and magnetism. We are very pleased to have worked with IOP on the conference proceedings, with special thanks to Dr Tom Miller and Dr Graham Douglas. Based on a refereed evaluation of all the papers and posters submitted, about 93 papers were selected for publication in the Journal of Physics: Conference Series and Superconductor Science and Technology.

The immensely rich and diverse scientific program started with Professor D Hampshire's opening plenary on 26 August 2008 and sessions were mostly chaired by the invited speakers. The topics included:

• New superconductors

• Theory and applications of MgB₂ and boride superconductors

• Hybrid magnetic-superconducting systems

• High temperature superconductors: theory and applications

• Superconducting devices and applications

• Oxypnictide superconductors

• Superconducting sources of THz-radiation

• Vortex dynamics

• Spintronics

• Superconductivity and magnetism at nanoscale

• Multiferroic materials

• Manganities

• Materials and fabrication techniques

• Conventional superconductors

• Microscopic theories of high temperature superconductors

• Device physics and thin films.

We believe that this conference, with the above topics, has provided a forum where the many matters of interest to the superconductivity and magnetism community have been debated. We are of the opinion that the conference has been a very successful one and we hope that the subsequent conferences in this field will constitute a series of fruitful meetings, by growing to become larger global events with greater success in bridging the gap between the best scientists, engineers, exhibitors and participants from countries underrepresented in science and technology.

The delegates and companions also enjoyed the social program in the touristic and historical places of the surrounding area, during the excursion time after 4.30pm on conference days. The welcome reception was held at the historical site of the Apollo Temple in Side and sponsored by the Municipality of Side; a second welcome party was also organized at the congress centre in the evening of 25 August 2008, for late-arriving participants. The social program also continued in the evenings with a variety of different entertainment.

The meeting was financially supported by generous contributions from Turkish research institutions, and an Italian firm, Columbus Superconductors SpA. The list of contributors is as follows:

• TÜBİTAK

• Boren

• Columbus Superconductors

• Ankara University Research Fund.

• Boronsan

• IMTEK

• Zeiss

• Nanomagnetics

• Optomek

• Side Municipality

• Belek Municipality.

It is a pleasure to thank them all for their pivotal role in the organization of the conference. We would also like to thank the speakers, the participants, the exhibitors and the Ankara University staff and students for their efforts which made ICSM2008 a very successful meeting. The list of people involved in the organization is given below. More information about the conference can be found at http://www.icsm2008side.org. It is due to the immense demand from most of the attendees that we are planning to organize the second International Conference on Superconductivity and Magnetism (ICSM2010) for April 2010, in Antalya. Further details will be made clear and circulated soon. We will be very happy to host the next conference and look forward to welcoming you again.

Conference Director A Gencer  Ankara University

Conference Co-directors B Aktas  GYTE, Gebze M E Yakinci  Inonu University

Scientific Committee D Abukay  IYTE, İzmir M Altunbas  KTU, Trabzon I Askerzade  Ankara University I Belenli  AIBU, Bolu G Grasso  Columbus Superconductors SpA, Genova N Guclu  G O Pasa University K Kiymac  Çukurova University S Nezir  Kirikkale University A Oral  Sabanci University B Ozcelik  Çukurova University Y Oner  IYTE, İzmir L Ozyuzer  IYTE, İzmir O Uzun  G O Pasa University E Yanmaz  KTU, Trabzon—Coordinator C Terzioglu  AIBU, Bolu

International Advisory Board M Tachiki  Tokyo University E Aksu  TAEK H Akalin  Renko O Atiker  Boronsan R Cubitt  Institut Laue-Langevin, Grenoble G Crabtree  Argonne National Laboratory A Elmali  Ankara University C Ferdeghini  CNR INFM, Genova R Flukiger  Genova University W Goldacker  FZ Karlsruhe C E Gough  Birmingham University R Huebener  Tubingen University K Kadowaki  NIMS, Tsukuba University M A R LaBlanch  UO, CA E Inger  Boren E Ozdas  Hacettepe University H Ozkan  METU, Ankara R Penko  ASG V Vlasov  Argonne National Laboratory

Scientific Programme Committee E H Brandt  Max-Planck-Institute, Stuttgart W Goldacker  FZ Karlsruhe C Ferdeghini  CNR INFM, Genova D M Hampshire  Durham University Y Oner  ITU, Instanbul B Aktas  GYTE, Gebze B Ramaev  GYTE, Gebze E Ozdas  Hacettepe University—Coordinator M A Aksan  Inonu University—Abstract Handling

Local Organizing Committee S Safran  Ankara University—General Secretary E Ertekin  Ankara University—Registrar A Kilic  Nigde University U Kolemen  G O Pasa University K Guven  Kirikkale University—Transport and Accommodation B Ozkurt  Mersin University Ö Çiçek  Renko D Bumin  Boren S Altin  Inonu University O Nane  Çukurova University

Editorial Board for Proceedings A Gencer  Ankara University—Guest Editor G Grasso  Columbus Superconductors SpA, Genova—Guest Editor B Aktas  GYTE, Gebze I Belenli  Hakkari University M A Aksan  Inonu University—Scientific Secretary M I J Probert  York University M E Yakinci  Inonu University A Bozbey  TOBB, University of Economics and Technology

Finance Director S Kervan  Nevsehir University

Bursary Coordinator H Agil  Ankara University

This is a co-publication with Superconductor Science and Technology. The International Conference On Superconductivity and Magnetism (ICSM2008) took place at The Congress Centre of Ankara University in Side-Antalya, Turkey, between 25–29 August 2008. The bulk of the papers, after peer review, are published in Journal of Physics: Conference Series. However a selection of papers, are published separately in a special issue of Superconductor Science and Technology.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The MgB₂ thick films have been fabricated on the polycrystalline YSZ substrates using spray pyrlosis technique. Structural/microstructural, electrical and magnetic properties were investigated by XRD, SEM-EDX and R-T measurements. The films fabricated showed dense and homogenous structural formation with strong grain connections. The electrical properties of MgB₂ thick films were investigated under different magnetic fields. It was seen that resistive transition broadened with increasing the applied magnetic fields. It was believed that the broadening is due to the thermally activated flux flow (TAFF). The activation energy, U(H), of the MgB₂ films was calculated using Arhenius law.

In this article, high T_c mercury based cuprate superconductors with different oxygen doping rates have been examined by means of magnetic susceptibility (magnetization) versus temperature data and X-ray diffraction pattern analysis. The under, optimally and over oxygen doping procedures have been defined from the magnetic susceptibility versus temperature data of the superconducting sample by extracting the Meissner critical transition temperature, T_c and the paramagnetic Meissner temperature, T_PME, so called as the critical quantum chaos points. Moreover, the optimally oxygen doped samples have been investigated under both a.c. and d.c. magnetic fields. The related a.c. data for virgin(uncut) and cut samples with optimal doping have been obtained under a.c. magnetic field of 1 Gauss. For the cut sample with the rectangular shape, the chaotic points have been found to occur at 122 and 140 K, respectively. The Meissner critical temperature of 140 K is the new world record for the high temperature oxide superconductors under normal atmospheric pressure. Moreover, the crystallographic lattice parameters of superconducting samples have a crucial importance in calculating Josephson penetration depth determined by the XRD patterns. From the XRD data obtained for under and optimally doped samples, the crystal symmetries have been found in tetragonal structure.

The HTS (High-Temperature Superconducting) synchronous motor has advantages over the conventional synchronous motor such as smaller size and higher efficiency. Higher efficiency is due to smaller loss than the conventional motor, so it is important to do loss analysis in order to develop a machine with higher efficiency. This paper deals with machine losses those are dissipated in each part of a HTS synchronous motor. These losses are analyzed theoretically and compared with loss data obtained from experimental results of a 1 MW class HTS synchronous motor. Each machine loss is measured based on IEEE 115 standard and the results are analyzed and considered based on the manufacturing of the test machine.

Bi-2212 single crystal whiskers have been fabricated on the surface of the bulk glass BSCCO pieces prepared by the melt-quenching process. The characterizations of the whiskers were made using XRD, SEM-EDX, M-T, M-H analysis. Pinning force calculations were performed using magnetic hysteretic loops taken at different temperatures and results obtained were analyzed using scaling law equation. The whiskers fabricated showed higher pinning at low temperature. The pinning force at 10 K was calculated to be 3,83x10¹¹ N/m³ under 2 T applied magnetic field. The results obtained showed that a decrease on the flux pinning force decreases the critical current density of whiskers.

Anomalous ferromagnetic behaviour of the Y₂O₃ and CuO components in YBa₂Cu₃O_y (Y123) was observed after severe reduction of particle size. The particle size reduction was performed in following way: Y₂O₃, BaCO₃ and CuO were ground for different times to reduce the particle size to the nanoscale. It was found that the superconducting phase could not be obtained without heat treatment, but a weak ferromagnetic behaviour of the mixture was observed at liquid and room temperatures. In order to understand which compound is responsible for this weak ferromagnetism, the Y₂O₃, BaCO₃ and CuO powders were separately ground and M-H loops taken at 290K. The results indicated that both Y₂O₃ and CuO powders showed weak ferromagnetism, but BaCO₃ showed anti ferromagnetism. It is thought that energy transfer to the powder particles by grinding results in severe plastic deformation of the particles to produce dislocations, vacancies and atomic disorder. We discuss then the observations in the context of recent studies of the magnetic properties of nanoscale oxide materials.

The dynamics of a disk-shaped permanent-magnet rotor levitated over a high-temperature superconductor is studied. The interaction between the rotor magnet and the superconductor is modelled by assuming the magnet to be a magnetic dipole and the superconductor as a diamagnetic material. In the magneto-mechanical analysis of the superconductor part, the frozen image concept is combined with the diamagnetic image and the damping in the system was neglected. The interaction potential of the system is the combination of magnetic and gravitational potential. From the dynamical analysis, the equations of motion of the permanent magnet are stated as a function of lateral, vertical and tilt directions. The vibration behaviour of the permanent magnet is analyzed with a numerical calculation obtained by the non-dimensionalized differential equations for small initial impulses.

The resistivity measurements of the Yb_1-xGd_xBa₂Cu₃O_7-y superconducting samples prepared by using the solid-state reaction technique for x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were performed in QD-PPMS system under different magnetic fields up to 5T in zero field cooling regime. The upper magnetic field H_c2(T=0) for each sample was calculated from 50% of the normalized resistivity (R_n) by the extrapolation H_c2(T) to T=0K and the coherence lengths ζ(T=0) of the samples were calculated from the H_c2(0) values. The examination of the effects of x in the composition on H_c2(0) showed us that the upper critical magnetic field decreased from 186.31T for x=0.0 to 37.99T for x=1.0 with the increasing of content x from x=0.0 to 1.0. Using the content x in the composition, the upper critical magnetic field can be controlled and this can be used in superconducting application especially as a superconducting relays.

The electrodynamic response of a two-junction symmetric quantum interferometer, containing two equal 0-junctions and enclosing a superconducting nanocylinder, is studied by means of a first order perturbation analysis of the dynamical equations obtained for the composite system in the absence of noise. It is shown that, when an appropriate number of fluxons is trapped in the inner superconducting cylinder, the system behaves like a π-SQUID.

Peak effect in dependences of critical current density on applied magnetic field caused by nanosize chemical pinning centers was studied in Y_1.5Ba₂(Cu,M)₃O_y, for M = Ag, Mn, and Al with CeO₂ technological addition. The behavior of Mn, Ag and Al dopants was analyzed in relation to sample microstructure and oxygenation heat treatments respectively. It is shown that formation of Cu₂Mn₃Ba₆O_ycompound and low negative partition coefficient of Ag between the solid and melt are responsible for declination from expected pinning behavior for Mn and Ag substituents.

MgB₂ polycrystalline superconducting specimens were irradiated with 10 MR and 20 MR doses of γ-rays. An increase in the normal state resistance and a broadening of the resistive transition to the superconducting state were observed with increasing γ-irradiation dose within the temperature range of 28 –31 K. The change in the critical temperature, T_c was found to be insignificant after irradiation. The critical current density, J_c was found to be enhanced almost at all temperatures after irradiation. The enhancement of J_c was found to be linear with the irradiation dose at all temperatures. These results are explained by the effects of γ-rays and temperature on the migration of MgO impurities into the grains and the oxygen segregation in the grain boundaries.

In this study, production methods and the structural and magnetic properties of melt-textured growth of YBa₂Cu₃O_7-x bulk superconductors are discussed. During the research; various temperatures for melt texturing are tried for the optimization of the production of bulk YBCO. With the help of AC magnetic susceptibility measurements, some insights for the produced samples are handed out including critical phase transition temperatures and the effects of crystal growth inside the YBCO samples. XRD measurements showed bigger and greater number of crystal growth in a correlation with the increasing temperature and the microphotographs of the samples verified successive growth of YBCO crystals inside the samples. Sharper phase transition is reached with the increasing texturing temperature. Top seeding for the selected crystal orientation has also been tried at the 1070oC for the texturing temperature, but the resulting melt textured sample was not different with the only-textured sample in the means of magnetic properties. Optimization over the texturing temperature found out to be between 1070oC and 1080oC while this result only depends on magnetic and structural properties.

We have investigated the effect of annealing temperature on the microstructure, magnetic and mechanical properties of MgB₂ superconducting samples employing X-ray diffraction (XRD), scanning electron microscopy (SEM), ac susceptibility and Vickers microhardness measurements. XRD patterns and SEM micrographs are used to obtain information about lattice parameters and grain size, respectively. These measurements indicate that MgB₂ grain size, lattice parameters, and critical temperature are increased, and grain connectivity is improved, with increasing the sintering temperature up to 850°C. It is also observed that the Vickers microhardness of the samples is dependent of the sintering temperature and applied load. In addition, we calculate the load dependent mechanical properties of MgB₂ samples such as the Young's modulus, yield strength, and fracture toughness. The possible reasons for the observed improvements in microstructure, superconducting and mechanical properties due to annealing temperature are discussed.

The barrier layer of self-ordered anodized aluminium oxide, which is grown from an aluminium foil, has been revealed by a selective chemical etching of the remaining aluminium. The surface obtained in this way consists of a triangular lattice of bumps with 100nm spacing, and heights of approximately 50nm. Using this surface as a template for controlling the pinning in thin superconducting films, superconducting Nb was deposited with different thicknesses and under different deposition angles. The evaporation under a 30° angle shows an asymmetric pinning potential composed of two triangular lattices having different pinning strengths. Matching effects are observed up to 1T. Matching effects are also maintained at relatively low temperature.

A series of studies has been carried out on thin films which were prepared by pulsed laser deposition from micro-grained targets of Y_1-xPr_xBa₂Cu₃O_7-δ (Y_1-xPr_xBCO) to determine the doping effect of Pr (at Y site) in concentrations between x = 0 –0.20. Earlier results on bulk materials show that the Pr substitution can significantly enhance the value of J_c(B) at cost of T_c. Our X-ray diffraction results confirmed the good quality of the films without any impurity phases. Magnetometric studies show the systematic decrease of J_c(B) when the Pr concentration is increased.

The nanometer-scale correlated pinning disorder filling channels between regular twin boundaries in the melt-textured (Nd,Eu,Gd)Ba₂Cu₃O_y composite is studied. Aligned with regular twin boundaries but tightly packed on nm-scale, this pinning medium is capable to significantly enhance pinning performance at high magnetic fields. We show that oxygen annealing plays a principal role in the formation mechanism of this defect type. It seems that the nanoscale lamelar structure is extremely sensitive to the oxygenation procedure and to the terminal temperature.

In this study, YBCO thin films on single crystal LaAlO₃ (100) substrates have been grown using DC inverted cylindrical magnetron sputtering technique and the effect of the deposition rate on these films is investigated. Three different deposition rates are used to produce superconducting YBCO thin films with 150 nm of thickness on (100) LaAlO₃ single crystal substrate at 780 0C. The samples are analyzed in detail by means of XRD, R-T, χ-T, M-H and AFM characterizations and also the critical current densities (J_c) are derived from the magnetic hysteresis curves using the modified Bean formula [1]. The critical current density at 50 K was found to be in the range of 3.10⁷ A/m² to 8. 10⁷ A/m² with a deposition rate between 2nm/min and 1.2nm/min. A correlation has been obtained so that as the film deposition rate increases, the surface smoothness and crystalline quality of the films significantly deteriorate, resulting in a significant decrease in J_c.

In this work, we have investigated and presented the bolometric response of freestanding membrane type of superconductive transition-edge detectors at micro-scale and submicron-scale substrate thicknesses. The technique applied here is based on the finite-size scaling method which is now extensively used for the calculation of thermal parameters of materials at low dimensions when the significance of surface energy contribution is not negligible compared to that of the total bulk energy. This method is used to evaluate the variation of specific heat per unit volume and heat conductivity and hence its effect on the total heat capacitance and conductance of the substrate versus its thickness. By using the thermal parameters obtained from the applied method we calculated the IR response in these types of the devices. This response when inspected at low thicknesses of substrates showed anomalistic behavior with respect to previous response analyses. Discussed in this paper, we also obtained the optimized substrate thickness for maximum responsivity of the device. The obtained results are compared to previous response calculations and experimental measurements.

The critical current and n-value of the HTS tape, which are important for the characteristic analysis of the 600kJ HTS SMES system, were studied, and based on the results of the study, the DC V-I characteristics of a model coil fabricated by the same HTS tape of a 500 m length conductor were analyzed. The result show that the measured critical current and n-value of the conductor for parallel field are constant in external magnetic fields less than about 0.2, whereas the characteristics decreased for the whole range of the oblique magnetic field. The critical current of the coil, which was calculated based on the results of the study on a short sample conductor, corresponded to the obtained value, which means that the critical current and n-value of a conductor for an oblique magnetic field in an arbitrary direction in the HTS SMES system can be estimated only by using the DC V-I characteristics of a short sample conductor for parallel and perpendicular magnetic fields.

Flattened MgB₂ superconductors have an advantage of increased filament density and consequently high transport current density. On the other side, flat rolling is introducing the texture into MgB₂, which leads to critical current anisotropy. Therefore, MgB₂ tapes prepared from different precursor powders (ex-situ, in-situ and mechanical alloying) deformed in several metallic sheaths were measured in the external magnetic field of variable orientations. Critical current anisotropy of these composite tapes are compared and discussed.

Sample of Y_1-xPr_xBa₂Cu₃O₇ with x = 0.0 to 0.80 are synthesized by solid- state reaction route. All the samples crystallized in orthorhombic structure with space group pmmm. Slight decrease in orthorhombicity is seen with an increase in Pr content. Superconductivity is destroyed above 50% Pr content. Non-superconducting samples are highly semi conducting. Detailed high field magnetization (M-H) measurements showed that the lower critical field (H_c1) improves slightly with Pr content of up to 4% and the same later decreases for higher Pr contents. The critical current density calculated by invoking Bean's critical state model improves dramatically until x=0.04 and decrease later for higher Pr contents in comparison to the pristine sample. These results are explained on the basis of Pr^4f and O^2p hybridization induced disorder in superconducting CuO₂ planes. For low Pr content the mild disorder in superconducting condensate (CuO₂ plane) induces intrinsic pinning and hence resulting in an increased J_c(H) and H_c1.

The flexural strength of 1 wt.% Ag-doped Bi₂Sr₂CaCu₂O_8+δ thin rods textured by a laser heated floating zone was measured as a function of the environmental conditions (air versus water) at room temperature. Loading rates spanning three orders of magnitude (1, 10 and 100 μm/min) were used to explore their susceptibility to the environmental conditions. These mechanical tests were completed with electrical characterization (critical current at 77K and resistivity from 77 to 300 K) of samples submerged in distilled water for different time lengths (0, 12 and 120h). While Bi₂Sr₂CaCu₂O_8+δ has been shown, in previous works, to be unstable during contact with water molecules, the Ag-doped Bi-2212 textured rods tested in this work are very inert to the water environment, with respect to their mechanical and electrical properties, due to the presence of a narrow (≈150 μm) low textured outer ring formed in the growth process.

(Bi,Pb):2223 superconducting samples were obtained by using solid state reaction method. The effect of partial substitution of Ca by R=Sm, La on the structural and magnetic properties of (Bi_1.6Pb_0.4)(Sr_1.8Ba_0.2)(Ca_1-xR_x)₂Cu₃O_y with 0≤ x ≤0.05 were investigated by XRD and ac magnetic susceptibility measurements. The intergranular critical current density function of temperature J_cJ(T), were obtained and agree with the SNS behavior of grain boundaries.

We have investigated various characteristic properties depending on sintering conditions of MgB₂ samples prepared by the standard solid state reaction method. It is inferred from experimental results that the crystallinity of samples were improved when the pressure of the Ar ambient increased. Also, it was found that the sintering temperature above 850 °C caused extremely high amount of decomposition of the superconductor phase. Finally, it was considered that the sintering process of MgB₂ must be carried out under the pressure of Ar ambient higher than 8 bar to impede the volatility of Mg in the structure of MgB₂. The J_c values of samples systematically enhanced with the increase of sintering time and in particular, the sample sintered for 180 min. exhibited the highest J_c (0) of 4.9 × 10³ A cm^-2 at 30 K. The obtained results demonstrate that the sintering conditions of MgB₂ have a significant influence on T_{c (onset)} and J_c, which are directly related to practical applications of MgB₂ based superconductor components.

We report on low-field magnetic properties of gold diffusion-doped Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃O_y superconducting bulk samples by performing ac susceptibility measurements. The undoped samples were prepared by the standard solid-state reaction method. Doping of Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃O_y was carried out by means of Au-diffusion during sintering from an evaporated gold film on pellets. To investigate the effect of gold-diffusion and diffusion-annealing duration on transport, magnetic and microstructure properties of the superconducting samples we performed magnetoresistivity, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. The ac susceptibility as a function of temperature measurements were carried out at different values of the ac magnetic field amplitudes (Hac) in the range between 20A/m and 320 A/m for 211 Hz. The imaginary part of ac susceptibility measurements is used to calculate intergranular critical current density J_c(T_p) using the Bean Model. J_c(T_p) is seen to increase from 60 A cm^-2 to 90 A cm^-2 with increasing diffusion-annealing time from 10 h to 50 h. The peak temperature, T_p, in the imaginary part of the ac susceptibility is shifted to a lower temperature with decreasing diffusion-annealing duration as well as increasing ac magnetic fields. The force pinning density (α_jj (0)) increased with increasing diffusion annealing time. The value of T_c in gold-diffused samples, in comparison with the undoped samples, increased from 100 ± 0.2 K to 104 ± 0.2 K. It was observed that the value of T_c-offset of the gold-doped samples enhanced with further increasing diffusion-annealing duration. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size of the samples. Gold doping enhanced the formation high-T_c phase and increased the grain size. The possible reasons for the observed improvements in transport, microstructure and magnetic properties due to Au diffusion and diffusion-annealing time were discussed.

DC magnetron sputtering technique were used for the synthesis of high quality epitaxial thin films of the superconducting cuprate Bi2Sr2CaCu2Oy (Bi: 2212) thin films. The structural characterization carried by X-ray diffraction indicates that the films are single phase and oriented with their c-axis perpendicular to the substrate surface. The flux motion mechanisms in the vicinity of the irreversibility line have been studied by AC susceptibility technique. The temperature dependencies of real and imaginary parts of AC susceptibility were performed, by using different values of amplitude and frequency. Temperature dependence and low field dependence of the activation energy for flux motion were obtained

Solid state reaction method was used to synthesize the high-T_c superconducting material with nominal composition Bi_1.6Pb_0.4Sr_1.6Ba_0.4Ca₂Cu₃O_y. This paper investigates the associations among macroscopic physical properties and features at atomic level for the prepared samples. The samples were preliminary analyzed by dc electrical resistivity and ac magnetic susceptibility. After that thermal transport, electrothermal conductivity and thermoelectric properties all as a function of temperature (from room down to liquid nitrogen temperature) were measured. X-ray diffraction studies were also done for structural analysis. All the above measurements showed that in the samples, there exists almost a single high- T_c phase with T_c,0 ∼ 110±1K. The lattice constants of the material were determined by indexing the diffraction peaks. Samples were investigated for thermal transport properties, i.e. thermal conductivity, thermal diffusivity and heat capacity per unit volume. Thermal transport properties were measured by a newly developed and calibrated Advantageous Transient Plane Source method. Simultaneous measurement of thermal conductivity and thermal diffusivity made it possible to estimate specific heat and the Debye temperature T_D. Thermoelectric power (Seebeck Coefficient) and electrothermal conductivity were also measured with a recently developed and attuned apparatus. Using dc electrical resistivity, thermal conductivity and thermoelectric power, the Figure of merit factor was also calculated.

We study the controllable manipulation of vortices in a mesoscopic, superconducting "island" of Nb, using an integrated Josephson junction as a field-sensitive vortex detector. The island, divided by a single Josephson junction and suspended by Nb microbridges, was fabricated from a Nb/P_11-xNi_x/Nb tri-layer using a focused ion beam. We find that the system at select magnetic fields behaves as a vortex memory cell, where current pulses can be used to switch the vortex configuration between metastable states of distinctly different junction critical currents. Non-destructive read-out of a state is then easily done with an intermediate current. Furthermore, we show that the Josephson junction displays a strong magnetoresistive effect at current bias well above the junction critical current but below the onset of flux flow. This enables the junction to be used as a quantitative probe of magnetic field with better than single flux quantum resolution.

Superconductivity has been found in two Li-containing compounds, Li₂Pt₃B and Li₂Pd₃B, which show superconducting transition at temperatures 2.5 K and 7.2 K, respectively, and have the same cubic structure (P4₃32) without mirror or inversion symmetry. Because the compounds are noncentrosymmetric, it is interesting to study the symmetries of the superconducting gap function and Cooper pairs. The specific heat of Li₂(Pt_1-xPd_x)₃B [x = 0, 0.5, 1] was measured. The Pd-concentration (x)-dependent electronic specific heat (C_es) of Li₂(Pt_1-xPd_x)₃B at low temperatures <<T_c showed distinctly different features on varying x. The temperature dependence of C_es for one end member, Li₂Pd₃B, follows an exponential behavior as in conventional superconductors, while those of Li₂Pd_1.5Pt_1.5B and Li₂Pt₃B follow a quadratic one, suggesting the existence of line nodes in the superconducting gap. This contrasting result conceivably originates from the difference in the strengths of the spin-orbit coupling of the Pt- and Pd-based compounds.

The effect of the cooling rates on oxygen content of silver sheathed Bi-2223 bulk superconducting samples was investigated performing dc electrical resistivity, transport critical current density, ac susceptibility and x-ray diffraction (XRD) measurements. The bulk samples with Ag sheathing were annealed under identical conditions and cooled with rates of 25° C / h, 50° C / h, 75° C / h, and 100° C / h. We estimated the transition temperatures from both dc resistivity and ac susceptibility as a function of temperature measurements. It is observed that T_c and J_c depend on cooling rates of the samples. T_c and J_c decrease with increasing cooling rates. The imaginary part of ac susceptibility measurements is used to calculate inter-granular critical current density using the Bean Model. J_c(T_p) is also seen to decreases with increasing cooling rates. The peak temperature, T_p, in the imaginary part of the ac susceptibility is shifted to a lower temperature with increasing cooling rates as well as increasing ac magnetic fields. The force pinning density decreased with increasing the cooling rates. XRD patterns are given to determine lattice parameter c and obtain information about Bi-2223 and Bi-2212 phases.

We calculate, using the time-dependent Ginzburg-Landau (TDGL) equation with thermal noise, the transverse thermoelectric conductivity α_xy, describing the Nernst effect, in type-II superconductor in the vortex-liquid regime. The method is an elaboration of the Hartree-Fock. An often made in analytical calculations additional assumption that only the lowest Landau level significantly contributes to α_xy in the high field limit is lifted by including all the Landau levels. The resulting values in two dimensions (2D) are significantly lower than the numerical simulation data of the same model, but are in reasonably good quantitative agreement with experimental data on La₂SrCuO₄ above the irreversibility line (below the irreversibility line at which α_xy diverges and theory should be modified by including pinning effects).

In this study, we propose a wet chemical method, called ammonium-nitrate-melt-technique, for the synthesis of any type of bulk oxide compounds. This method was successfully applied to the high-T_c superconductors (Y-123, Ru-2212, etc), diluted magnetic semiconductors (Ti_1-xCoO₂) and hard magnetic barium ferrites (BaFe₁₂O₁₉). For instance, we have obtained a single phase M-type barium ferrites with finely granular structure at nanoscale (300-400 nm). Magnetic parameters of these samples are near to the theoretically estimated values. Besides, superconducting transition temperature of ∼70 K was observed in ferromagnetism&superconductivity co-existed ruthenates, which is only possible at very high oxygination pressures (600 atm). Consequently, we believe that the method will attract the attention of many material scientists.

Samples of commercially available BiSCCO-2223/Ag tape have been partially covered by the ferromagnetic material. Improvement of the self-field critical current up to 15 % has been achieved by this procedure. A critical current of such tape strongly depends on geometric and magnetic properties of both, the superconducting tape as well as the ferromagnetic cover. Numerical simulations, based on the critical state model using commercial finite element method (FEM) code, have been performed. Properties of superconductor are characterized by anisotropic dependence of the critical current density on magnetic field as well as detail geometry of filaments. The ferromagnetic material is characterized by nonlinear magnetization curve. Nonlinear dependences of the critical current on selected parameters are shown in this work. Optimization of the cover parameters using these curves has been made. Samples with various parameters have been manufactured for the confirmation of numerical simulations results. Experimental results are in good qualitative agreement with results obtained by numerical simulations.

Deposition of high temperature superconducting thin films by pulsed laser deposition (PLD) started a flurry of activities in the area of rare earth class of oxide manganites. Studies have been carried out by injection of the polarized spins from a ferromagnetic metal, into the superconductor via a thin insulating barrier. However because of the presence of an insulating layer possible role of joule heating in limiting the spin polarized transport across the interface cannot be ruled out. We would like to present some of the results of our work carried out on LaAlO₃/La_0.7Ca_0.3MnO₃/YBa₂Cu₃O_7-δ (LAO/LCMO/YBCO) LCMO on top and LaAlO₃//YBa₂Cu₃O_7-δ La_0.7 Ca_0.3 MnO₃ (LAO/YBCO/LCMO) YBCO on top heterostructures deposited on <100> LAO substrates without any insulating layer separating the two. PLD technique was used to deposit a 500 micron wide line of LCMO followed by deposition of YBCO layer which was subsequently patterned into a 500 micron line directly on top of the LCMO line. Here we report the suppression in the critical current I_c of the superconductor due to pair-breaking phenomenon when polarized spins are injected into YBCO in case of LAO/LCMO/YBCO (LCMO on top) sample. Surface and interface characterization of these bilayers was performed by SQUID, AFM, SIMS and four probe techniques.

The Hilbert spaces representing the quantum states in the CuO₂ planes are not spanned by crystal symmetry adapted basis states, but by self-consistently renormalized states which form compound systems of Hilbert subspaces. In addition, these self-consistent basis representations are not necessarily stationary in time but behave dynamic in many respects. In particular, the coordinate systems of the Hilbert subspaces form a definite dynamic relative state in space and time, thus the coordinate system itself becomes a variable. This implicates a deterministic space-time relation of quantum states and the quantization of time by an internal time constant, the eigentime t_eiDCBF. In undoped and hole doped CuO₂ planes t_eiDCBF occurs as a conservation quantity, whereas under electron doping a partial fluid exists in which t_eiDCBF does not occur as quantized quantity. The deterministic space-time behaviour of the Hilbert subspaces represents the emergence of a classical space-time structure in quantum systems. The metal-insulator transition in high-T_c cuprates, usually attributed to an antiferromagnetic Mott transition, results here from an additional splitting into Hilbert subspaces. The transition from the insulator to the conductor is causally related to coordinate transformations from the copper to the oxygen sites. The antiferromagnetism in the CuO₂ planes is not caused by the half-filled valence bands, as usually assumed, but is created by off-diagonal spin compensations within filled bands.

The torque transferring mechanism taking place in a superconducting mixer design has been studied. Several coupling magnetic arrangements were investigated for more details in the engineering design. A bulk superconductor sample was used to study the torque forces for various cooling gaps, and the twist angle dependence was also monitored for the rotational stiffness in stability. The experimental data with four permanent magnet configurations have been studied in the present work. The maximum torque forces are summarized for usage of engineering design with various gaps. The torque/gap characteristics for four configurations were also measured for the optimisation of the torque at a designed operating gap.

In this paper, a study regarding the epitaxial growth of Ce_xZr_1-xO₂ film on biaxially textured Ni-5at.%W substrate and its use as a single buffer layer of a YBCO coated conductors was reported. Films of Ce-Zr mixed oxide were prepared by direct-current (d.c.) reactive magnetron sputtering with the two sputtering guns arranged symmetrically with respect to the substrate. In sputtering process, d.c. power of Zr was fixed in 200 W while that of Ce was varied with 30 W, 50 W, 75 W, and 100 W, respectively. It was confirmed that the composition of the films could be controlled with modulating power of Ce target. All samples exhibited good epitaxial growth with c-axis perpendicular to the substrate surface. Atomic force microscope revealed a continuous, dense, and crack-free surface morphology for Ce_0.32Zr_0.68O₂ thin films, which provided themselves as the good single buffer to the YBa₂Cu₃O_7-δ (YBCO) coated conductors. High quality Ce_0.32Zr_0.68O₂ buffer layers up to 100-m length could be fabricated with production speed of about 1.2m/h. X-ray scans have been performed as a function of length to determine the crystallographic consistency of the epitaxial Ce_0.32Zr_0.68O₂ over length.

This paper reports the effect of Pr substitution on lattice anharmonicity contribution to temperature dependent longitudinal and shear ultrasonic velocity data in (Er_1-xPr_x)Ba₂Cu₃O_6.9 (x = 0.0, 0.1 and 0.2) and TlSr₂(Ca_1-yPr_y)Cu₂O₇ (_y = 0.5 and 1.0) superconductors. Pr was observed to influence the deviation of the elastic behaviour of both samples from the lattice anharmonicity curves at higher temperatures. The calculated effective Gruneisen parameter for the longitudinal mode (γ_eff^L) for both compounds was found to increase with Pr content, indicating increasing anharmonicity contribution. In addition, both series also showed that γ_eff^L is larger than the effective Gruneisen parameter for the shear mode (γ_eff^L) throughout the substitution. The influence of Pr substitution on γ_eff and the BCS electron-phonon coupling constant (λ) as well as its possible relationship to superconductivity are discussed.

We investigated the effect of cooling rates on the microstructure and mechanical properties of Bi_1,6Pb_0,4Sr₂Ca₂Cu₃O_y superconductors prepared by standard solid state reaction methods. The samples were annealed under identical condition and cooled with different cooling rates. The investigations consisted of Vickers microhardness, SEM and XRD measurements. XRD examination of the samples showed that high percentage of Bi-2212 phase was observed and low-T_c phase increased with increasing the cooling rates. From SEM analysis, flake-like grains were more pronounced with increasing cooling rates. The indentation load versus diagonal length of the samples under different indentation loads in the range of 0.245-2.940 N were presented. We calculated Vickers hardness, Young's modulus, yield strength, fracture toughness values. These mechanical properties of the samples were found to be load and cooling rate dependent. In addition, we calculated the load independent microhardness, Young's modulus, and yield strength and fracture toughness of the samples using different models. The possible reasons for the observed changes in microstructure and mechanical properties of the samples due to cooling rates were discussed.

In cuprate oxide YBCO superconductor, Pr-doping is an interesting project for a long time. The reason is that many experiments have shown that of all the rare earth elements, only Ce, Pr and Tb are exceptive, does not result in superconducting samples while with the same crystal structure as other Y123 superconductors. Here, CeBa₂Cu₃O_7-δ and TbBa₂Cu₃O_7-δ isn't crystalline stable, while Y_1-xPr_xBa₂Cu₃O_7-δ(YPr123 systems) is easily formed in single-phase structure for all Pr content x=0.0-1.0. Therefore, to understand the question why PrBa2Cu3O7-δ(Pr123) is not superconductor is possibly essential to help to determine the nature of the superconductivity. The typical general results for Pr substitution are that there are a monotonic decrease in T_c and eventually a metal-insulator transition with increasing Pr concentration and that there are also ion size effect which shows that in R_1-xPr_xBa₂Cu₃O_7-δ (R=Rare Earth), Pr suppressed superconductivity more seriously as the rare earth's radius increase. Theoretically, some models, such as magnetic pair breaking, hole filling, carrier localization, and so on, have been proposed to explain the phenomena above. Magnetic and pinning force behavior is a kind of important characteristics in both conventional superconductor and layered cuprate superconductor. Studies of flux behavior in superconductor are of interest from the viewpoints of both fundamental research and practical application. In order to explain the anomalous behavior of Pr123, in the present work, the magnetization and flux pinning results at various temperatures are reported for Y_0.93Pr_0.07Ba₂Cu₃O_7-δ (YPBCO) single crystals. The samples were prepared by top-seeded solution growth method. The magnetic field dependence of critical current density J_c, pinning force density F_p and the phase diagram are also given for YPBCO single crystals. The results show that the value of the ratio of the maximum pinning force field vs irreversibility field is at around 0.333. Flux pinning mechanisms is also discussed in different magnetic field by the scaling function as well as the ratio of the pinning force field at H_on and H_peak. The results are compared with doping free YBCO sample, which probably explains that Pr suppresses the superconductivity.

Fe_1.2In_1.87Se₄ single crystals have been fabricated by partial substitution of In atoms with Fe atoms in In2Se3 in vacuum with heat treatment up to 1270°K and then cooling to room temperature. Based on X-ray diffraction studies and crystallographic calculations it has been shown to crystallize into rhombohedral lattice with ZnIn₂S₄ type three-packet (layer) structure and with lattice parameters a=4.08, c=39.96Å, Z=3 and space group ^R3m. The dependence of the magnetic susceptibility of produced crystals with temperature has been investigated; it shows that a transition from ordered paramagnetic to disordered spin-glass state takes place below 19K.

First stage of formation magnetite nanoparticles is described by kinetics equation. Solution of kinetics equation is Gauss function. Mean value and standard deviation of Gauss function are , Critical size, determinant of collapse and growth of nanoparticles are determined. It's showed nanoparticles less critical size may be is collapsed, bigger — grow. The dependence of the size and speed of the growth size on time are determined.

The dispersion relation for magnetic polaritons localized at the antiferromagnetic impurity film in the antiferromagnetic superlattice (antiferromagnetic/nonmagnetic or antiferromagnetic/antiferromagnetic) are derived in the effective-medium approximation and calculations are performed for the properties of long-wavelength electromagnetic modes. In such systems one finds both surface polaritons which are localized near the surface and guided modes where excitations have a standing-wave-like character and the impurity region acts as a waveguide, because of the magnetic polaritons propagating freely over the impurity layer and dampen in the perpendicular direction on either sides of this region. We assume an external magnetic field parallel to the magnetization and the film interfaces. The dispersion curves and frequency region of the existence of the surface-guided modes of the magnetic polaritons localized at the impurity layer of the antiferromagnetic superlattice are investigated for two values of the external magnetic field: H=0 and H=0.3T.

In the present study, using three-band Kane's model including the conduction band, light and spin-orbital hole bands, the electronic states of a semiconductor quantum anti-wire is studied in presence of Rashba spin-orbital interaction and external magnetic field and compared with those of a quantum anti-wire of the same size. It's calculated the radii, height, coupling strength and magnetic field dependence of Rashba splitting for carriers respectively. It has been found for the InSb quantum anti-wire that Rashba splitting of electrons are decreased with the increasing of radius.

Single crystals of ZnO, TiO₂ and LaAlO₃ have been implanted with Ar with 100 keV and different fluencies. The Ar implanted crystals showed a week ferromagnetic-like signal between 10 K and 400 K. Hysteresis curves obtained at room temperature allowed confirming the ferromagnetic behaviour of the implanted samples. Spin polarised first principles density functional calculations were performed in the case of ZnO considering Zn interstitials and O vacancies. No net magnetic polarisation was found for O vacancies, but in the case of Zn vacancies a magnetic moment of 1_μB was obtained.

La_0.7Ca_0.3MnO₃/CaO (LCMO/CaO) multilayers were deposited on (100) LaAlO3 substrates by pulsed injection metal organic chemical vapour deposition. The samples were characterised by X-ray diffraction, transport and magnetization measurements. An anomalous behaviour of the electrical resistance under applied magnetic field and an exchange bias effect for the magnetization are observed for the multilayers with thinner LCMO layers. These results suggest the existence of a short range antiferromagnetic coupling at the layer interfaces.

The effects of monovalent doping in the A-site on the structural, magnetic and magnetocaloric properties in La_0.65Ca_0.3M_0.05MnO₃ (M=Na, Ag, K) powder perovskite manganites have been investigated. Our samples have been synthesized using the conventional solid state reaction at high temperature. Rietveld refinements of the X-ray diffraction patterns at room temperature show that all our powder samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Magnetization measurements versus temperature in a magnetic applied field of 50mT indicate that our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature T_C is found to be 295K, 254K and 285K for M=Na, Ag and K respectively. From the measured magnetization data of La_0.65Ca_0.3M_0.05MnO₃ (M=Na, Ag, K) samples as a function of magnetic applied field, the associated magnetic entropy change close to their respective Curie temperature T_C and the relative cooling power RCP have been determined. The maximum magnetic entropy change, |ΔS^max_m|, in a magnetic field change of 5T is found to be 3, 5.16 and 3.54 Jkg/K for M=Na, Ag and K respectively. The La_0.65Ca_0.3K_0.05MnO₃ sample exhibits the largest RCP value of 295J/kg.

Nuclear magnetic resonance (NMR) has enormous potential for various applications in industry as the on-line or at-line test/control device of process environments. Advantage of NMR is its non-destructive nature, because it does not require the measurement probe to have a contact with the tested media. Despite of the recent progress in this direction, application of NMR in industry is still very limited. This is related to the technical and analytical complications of NMR as a method, and high cost of NMR analyzers available at the market. However in many applications, NMR is a very useful technique to test various products and to monitor quantitatively industrial processes. Fortunately usually there is no need in a high-field superconducting magnets to obtain the high-resolution spectra with the detailed information on chemical shifts and coupling-constant. NMR analyzers are designed to obtain the relaxation parameters by measuring the NMR spectra in the time domain rather than in frequency domain. Therefore it is possible to use small magnetic field (and low frequency of 2-60 MHz) in NMR systems, based on permanent magnet technology, which are specially designed for specific at-line and on-line process applications. In this work we present the permanent magnet system developed to use in the portative NMR devices. We discuss the experimental parameters of the designed Halbach magnet system and compare them with results of theoretical modelling.

ZnTe and ZnTe:Cr films were prepared onto glass substrates using thermal evaporation method. Structural properties of the prepared samples were analyzed using X-ray diffractometer, and the presence of ZnCrTe phase was identified along with poor crystallinity. Composition analysis was done using XPS and the Cr content in the film was found to be 0.05 atomic percent. Transmittance spectra were recorded using UV-Vis spectrophotometer. The valence state of Cr in ZnTe:Cr film is determined to be +2 using electron spin resonance (ESR) spectroscopy. Magnetic moment data as a function of magnetic field were recorded using Superconducting Quantum Interference Device (SQUID) magnetometer at temperatures 5, 77 and 300 K. The results showed minority ferromagnetic behavior even at room temperature. Magnetic domains were observed using Magnetic Force Microscopy and the average value of domain size is 3.7 nm.

In this study, (BiY₂)Fe₅O₁₂ (Bi:YIG) magneto-optic layers were deposited on Si(100) and glass substrates using a sol-gel process. Bi, Y and Fe based-precursors were dissolved using methanol and glacial asetic acid as a solvent and chelating agent respectively. The turbidity, viscosity, gel point and pH values of the prepared solutions were determined using turbidimeter, rheometer and pHmeter. The prepared xerogels were dried and used for DTA/TG analysis to determine heat treatment regime in thin film production. Based on DTA/TG results, the deposited films were annealed at 800°C for 2 hours in air. Inasmuch as the magnetic and morphological properties are important for applications such as superconductive material vortex investigations, the produced films were investigated in details. The structural properties of the coatings were characterized by using XRD, SEM-EDS and AFM. The magnetic properties of the films were evaluated by the substitution of Bi and process conditions using VSM. The obtained results are presented.

FePt nanoparticles were synthesis via high-temperature solution phase. Monodispersed 3.5 nm FePt nanoparticles were first obtained by reduction of FeCl₂.4H₂O and Pt(acac)₂. These preformed FePt nanoparticles were then combined with NaCl to prevent from sintering after annealing. The 1 micron salt particles were fabricated by ultra-sonic vibration method and used as the separating media. Annealing studies show that these salt-matrix FePt nanoparticles are stable after annealing at 700 °C for 4 h. The annealed FePt particles diameter increases from 4 to 25 nm as observed by TEM. The magnetic properties are largely affected by annealing temperature. The role of these salt particles on sintering of annealed FePt nanoparticles has been investigated.

FeNi-based alloys are commonly used as soft magnetic materials, exhibiting high permeability, low coercivity and high saturation magnetization. The present study is focused on the effect of the milling speed (vial and disc rotation speed) on the magnetic properties of nanocrystalline Fe-45 wt. % Ni powders. The phase analysis and the structural properties were characterized by the use of X-ray diffraction. Structural parameters including lattice parameter, crystalline size and lattice strain were obtained from Rietveld's powder structure refinement analysis of X-ray powder diffraction data. The magnetic measurements were performed, using a vibration sample magnetometer (VSM) at room temperature. The results showed that the higher milling speed leads to larger lattice parameter, lower crystalline size, higher saturation magnetization and lower coercivity of the investigated system.

Single crystals of manganese-implanted TiO₂ rutile have been investigated by electron paramagnetic resonance (EPR) technique at room temperature. ESR spectra have been interpreted to correspond to the transitions among the spin multiplet (S=3/2) of the paramagnetic Mn⁴⁺ ion. Characteristic six-line hyper-fine splitting of the ESR spectra resulting from the spin I=5/2 of the Mn⁵⁵ nucleus has been observed. Analysis of EPR spectra shows that manganese in TiO₂ rutile host substitutes for Ti⁴⁺ ions. Two equivalent Mn⁴⁺ centers have been observed in the EPR spectra in correspondence with two equivalent octahedral positions of Ti ions in the rutile structure. Parameters of the crystal field of orthorhombic symmetry on the Mn⁴⁺ centers have been obtained as result of computer modelling.

ZnTe and ZnTe:Cr films were prepared onto glass substrates using the thermal evaporation method. Structural properties of the prepared samples were analyzed using X-ray diffractometry, and the presence of a ZnCrTe phase was identified along with poor crystallinity. Composition analysis was done using XPS and the Cr content in the film was found to be 0.05 atomic percent. Transmittance spectra were recorded using UV-Vis spectrophotometry. The valence state of Cr in ZnTe:Cr film is determined to be +2 using electron spin resonance (ESR) spectroscopy. Magnetic moment data as a function of magnetic field were recorded using a Superconducting Quantum Interference Device (SQUID) magnetometer at temperatures of 5, 77 and 300 K. The results showed minority ferromagnetic behavior even at room temperature. Magnetic domains were observed using Magnetic Force Microscopy and the average domain size is 3.7 nm.

The electrical properties of Co/n-Si metal-semiconductor (MS) Schottky structure investigated at room temperature using current-voltage (I-V) characteristics. The characteristic parameters of the structure such as barrier height, ideality factor and series resistance have been determined from the I-V measurements. The values of barrier height obtained from Norde's function were compared with those from Cheung functions, and it was seen that there was a good agreement between barrier heights from both methods. The series resistance values calculated with Cheung's two methods were compared and seen that there was an agreement with each other. However, the values of series resistance obtained from Cheung functions and Norde's functions are not agreeing with each other. Because, Cheung functions are only applied to the non-linear region (high voltage region) of the forward bias I-V characteristics. Furthermore, the energy distribution of interface state density was determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. The results show that the presence of thin interfacial layer between the metal and semiconductor.

Magnetoresistivity of A₂^VB₃^VI-based compounds has been investigated (H∼0÷89 kE, T=0,5÷4,2 K). Oscillation of magnetoresistivity, Shubnikov de Gaas oscillation has been observed at high magnetic fields (H>30 kE). The charge carrier concentration and area of extreme cross section of Fermi surface by plane, perpendicular to magnetic field have been evaluated from oscillation period.

A⁵₂B⁶₃-based compounds are used as high effective thermoelectric transformers [1]. Recently, the interest to these compounds increases due to the perspectivities of widening of working temperature range and increase of thermoelectric efficiency of A⁵₂B⁶₃ compounds, doped by different impurities [2-6]. Therefore the investigation of fundamental characteristics of these compounds is not only extended our representation on band structure, also has a practical meaning.

In the present work the results of investigations of galvanomagnetic effects in layered A⁵₂B⁶₃ compounds which have rhombohedral structure and crystallize in sp.gr. D_3d (R^÷m) [1], are given. The layers in A⁵₂B⁶₃ compounds consist of five monoatomic hexagonal grids alternating in sequence in B(1)-A-B(2)-A-B(1). Atom B(2) has 6 nearest atoms B(1). The bond between B(1)-A-B(2)-A-B(1) layers-quintets is of weak Van-der-Vaals type, but in layers of B(1)-A and A-B(2) bonds have covalent character with small fraction of ionic bond.

Single crystals under investigation have been were grown by Bridgman method from components with stoichiometric relationship. It is known, that by synthesis of A⁵₂B⁶₃ compounds from the melt of stoichiometric structure are characterized by presence of a significant amount of own points defects conditioned by transition of A atoms into the position of B atoms. These antistructural defects are the acceptors. Concentration of holes is p∼10¹⁹cm^-3. Investigations have been carried out in temperature range 0,5÷300K and magnetic field up to 8 Tl. At galvanomagnetic investigations the sample is placed in the centre of superconductive solenoid. Measurements are carried out by selective method under the alternating current by 20 Hz frequency. The current magnitude does not exceed 1_MA. The current is directed along the layer plane, magnetic field is perpendicular to layer plane.

We have evaporated a series of Co_xCr_1-x thin films under vacuum onto Si (100) and glass substrates, with a perpendicular incidence. The thickness of the magnetic layer ranged from 17 to 220 nm, and the content chromium, from 0.12 to 0.20, values determined by means of Rutherford Backscattering Spectrometry (R.B.S.) spectra using SIMNRA programme. Microscopic characterizations of the films were done with X-ray diffraction (XRD) measurements and infer that all the samples were polycrystalline, with an hcp structure and show a <0001> preferred orientation, and with the grain size increasing with the chromium content decrease. Atomic force microscopy (A.F.M.) observations reveal very smooth film surfaces. The static and dynamic magnetic properties have been investigated by means of Alternating Gradient Field Magnetometer (A.G.F.M.), and Brillouin Light Scattering (B.L.S.) measurements. The saturation magnetization M_B was found to decrease from 1200 emu/cm³ to 220 emu/cm³ as the chromium content increases from 12%at. to 20%at, whatever the thickness is.

From the fit of the B.L.S. spectra, we have computed effective magnetic anisotropy factors, as well. All the results are discussed and correlated.

Definite regularity in the distribution of ferromagnetic, antiferromagnetic and superconducting elements is observed in the periodic table starting with the 4th period. Elements with superconductivity, by which d-shells start to fill up, are at the beginning of each period; then follow antiferromagnetics and ferromagnetics (in 4th period and lanthanides), or elements without any of the three listed order types (5th period and 6th period), in which the d (f)-shells continue to fill up almost exceedingly; then again appear superconductors by filling the p-shell up to the number is equal to 4. We calculated the radii of the external d (f)- and p-orbitals and the nearest to them orbitals with the Slater method. These trends were explained by distinction of degree of division of the external d (f)- or p-orbitals of the neighboring atoms in the crystal. Largest division occurs in ferromagnetics. In antiferromagnetics it is smaller than in ferromagnetics. It is demonstrated that in the superconducting crystals the external dor p-shells approach the nucleus of neighboring atoms are much closely those for ferromagnetic or antiferromagnetic crystals. Furthermore the external d- or p-shells of some elements in the 5th and 6th periods approach the deeper shells of neighboring atoms. Hence the electron in this shell is situated in neighboring atoms in a different electric field from its own. This fact is open to speculation that the separation of spin and charge in electron, disposed on the external d- or p-orbitals, is quite possible. The charges without spin become bosons. Spins that have the magnetic moments are ordered antiparallel in pairs. Magnetic field transfers this pair in a parallel state and a magnetic flux component along of magnetic field from the pair is equal to one fluxon (the quant of the magnetic flux).

Based on Mn-doped chalcopyrite ZnSiAs₂ the new dilute magnetic semiconductor with p-type conductivity was produced. The Curie temperature behaviour of the produced semiconductor is distinctly dependent on the Mn concentration: 325 K for 1 wt.% and 337 K for 2 wt.% of Mn, consequently. Magnetization, electrical resistance, magnetic resistance and Hall effect of mentioned compositions were studied. Temperature dependence of magnetization M(T) have complicate behaviour. For T ≤ 15 K the M(T) dependence is characteristic for superparamagnetic and at T > 15 K magnetization is sum of magnetizations of ensemble of superparamagnetic clusters and ferromagnetic phase contained frustration regions.

The geometry structure of Mn, P doped 64-atom supercell of GaAs (Ga_1-xMn_xAs_1-yP_y) was optimized and studied by the self-consistent full-potential linearized augmented plane wave method (FP_LAPW) based on the density functional theory (DFT). Cell parameters of both doped and undoped were calculated theoretically. Band structure, binding energies, partial density of states, mulliken charges, and electron density different of doped GaAs crystals were calculated and analyzed in detail. The results revealed that the both doped compounds are true half-metallic ferromagnets and the near distance doped one is a stable ground state.

CoPt and FePt compound films with L1₀ ordered structure have been intensively studied, due to their extremely high uniaxial magnetocrystalline anisotropy which makes them suitable for application in ultra high density magnetic recording media. A basic requirement in these type of media is the development of strong perpendicular magnetic anisotropy. The role of Ag underlayers in promoting strong (001) crystallographic texture and perpendicular magnetic anisotropy in post-annealed Ag/CoPt and Ag/FePt bilayers (BLs) has already been reported, along with a possible correlation between L1₀ formation and development of (001) crystallographic texture. In this work we present new data, which provide further evidence that there is indeed such a correlation during the annealing process of Ag/CoPt BLs. The most obvious manifestation of this correlation is the fact that the X-ray intensity ratios I₀₀₁/I₀₀₂ (used as a measure of the degree of L1₀-ordering) and I₀₀₂/I₁₁₁ (used as a measure of the crystallographic texture) and the coercivity H_c and relative remnant magnetization m_r (for field H normal to the surface of the films) exhibit the same kind of dependence from the thickness of the Ag underlayer. Comparison with respective crystallographic data from post-annealed Ag/CoPt nanocomposites (NCs) shows that in the case of NCs the (001) texture starts to degrade for lower total film thickness, compared to the case of BLs. This difference can be attributed to the structural incoherence in the growth of the CoPt grains imposed by the presence of Ag inside the Ag/CoPt NCs, while in BLs Ag is only used as an underlayer. Based on the above data and on detailed Heavy Ion Elastic Rutherford Back Scattering (HIRBS) measurements, performed on post-annealed Ag/CoPt NCs, we propose a possible mechanism for the interpretation of the observed correlation. The proposed mechanism is based on the reduction of total strain (residual strain of as-deposited film and transformation strain due to deformation of the unit cell as L1₀-CoPt is formed) throughout the annealing process.

Yittrium iron garnet, Y₃Fe₅O₁₂ (YIG), is a material used widely in electronic devices for the microwave region as well as the magnetic bubble domain-type memories. Yittrium iron garnet (Y₃Fe₅O₁₂) was produced by mechanochemical synthesis from Y₂O₃ and Fe₂O₃ with particle size of around 150 nm. PMMA/YIG composite films were prepared by solution casting method at diffferent concentration (i.e. 10%, 20% and 40%) of YIG filler. Dielectric permitivity of composite materials were studied over a wide a range of frequency and temperature as a function of filler concentration. The electrical properties of composites were explained by in terms of molecular mobility and interfacial polarization.

We describe an experiment which investigates the effect of a longitudinal electric field on the spin-polarized carriers generated by a circularly polarized light in semiconductors. Our experiment observes the effect as a Hall voltage resulting from nonequilibrium magnetization induced by the spin-carrier electrons accumulating at the transverse boundaries of the sample as a result of asymmetries in scattering for spin-up and spin-down electrons in the presence of spin-orbit interaction. It is found that the effect depends on the longitudinal electric field and doping density as well as on temperature. The results are presented by discussing the dominant spin relaxation mechanisms in semiconductors.

Low field magnetic and magnetocaloric properties of the compound LaMn_1.9Fe_0.1Si₂ have been investigated. Using the M-H data measured at various temperatures, we have derived the magnetic entropy change ^|ΔS| as a function of temperature and magnetic field, by using the Maxwell relation. The temperature dependence of the Landau coefficient has been derived by fitting the magnetization, using the Landau expansion of magnetic free energy and Arrott plots. The results show that LaMn_1.9Fe_0.1Si₂ is ferromagnetically ordered around room temperature (285 K) and the nature of the phase transition at this temperature is found to be second order.

From the physical point of view multiferroics present an extremely interesting class of systems and problems. In the present article we report our results from magnetic properties measurements on orthorhombic ReMn₂O₅ single crystals (Re = Ho, Tb). The inherent magnetic frustration in these materials is lifted by a small lattice distortion, primarily involving shifts of the Mn³⁺ cations and giving rise to a canted antiferroelectric phase. In both compounds a colossal magnetostriction effect was observed and a novel phase transition diagrams, which indicate the correlation between magnetostriction and polarization for these two compounds were build.

The wide band gap semiconductor ZnO when doped with a very low percent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a unique compound for spin-electronic applications. In the present work we have compared the electronic structure of two polycrystalline Zn_1-xMn_xO pellets (for x=0.02 and 0.04), prepared by low temperature processing, and carefully characterized. The Rietveld refinement of the XRD patters established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The pure ZnO pellet shows a diamagnetic behaviour, the 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering even upon cooling. Their electronic structure has been investigated using x-ray absorption and x-ray photoemission spectroscopy with an aim to find out how the changes in the electronic structure can correlate to the magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to exactly predict that which of these two factors weighs more.

The structural and magnetic properties of yttrium iron garnet particles, synthesized in an ammonium nitrate melt (ANM), were investigated by magnetization measurements, XRD analysis and SEM microscopy and compared with that of the samples prepared using a solid state reaction (SSR) route. The phase formation of YIG starts at lower temperatures with the ANM technique and then develops with increasing temperature and sintering time. An almost single-phase sample was obtained by annealing for 2 hours at 1300°C, after which the YIG fraction in the SSR sample was only 0.34. Similarly, saturation magnetization of the samples sintered in the same conditions is always higher in the samples sintered via the ANM technique. SEM micrographs were used to determine particle sizes of the ANM samples which vary from the sub-micron to the micron range depending on the sintering temperature. These samples have uniform structures, small grains, better magnetic properties and do not contain massive agglomerates. As a result, the synthesis of YIG via the ANM technique represents another alternative to the SSR route.

Co-doped plain gels (PAAm) were prepared with and without pyranine fluoroprobe (8-hydroxypyrene-1, 3,6-trisulfonic acid, trisodium salt; POH), which have a OH- reactive group and three SO^-₃ ionic groups. Magnetization and fluorescence measurements were used for characterization of the gels. It was observed that both the plain gel itself and the gel including only POH (PAAm-POH) have a diamagnetic response to the external field. When the gels were synthesized together with cobalt (PAAm-Co) and cobalt/POH (PAAm-Co-POH), both gels magnetized in the direction of the magnetic field, as expected. However, the magnitude of the magnetization was different in the gels which were synthesized in the presence of POH and the one into which POH molecules were diffused after the synthesis, even though they have the same cobalt concentration. Fluorescence measurements and SEM micrographs were used to understand this surprising difference in the magnetization of PAAm-Co-POH gels. It was proposed that the electrostatic interaction between SO^-₃ groups of POH and free electrons of cobalt (Co⁺²) atoms led to the formation of Co-POH clusters having fewer unpaired electrons, and this results in a decrease in overall magnetization. It was also observed from the SEM images that the size of clusters depends on the Co-POH composition.

Thin films of Heusler alloys Co₂MnSn and Co₂MnGe prepared on sapphire a-plane substrates by RF-sputtering have been investigated by ferromagnetic resonance (FMR) technique. The magnetic anisotropies of the Co₂MnSn and Co₂MnGe thin films have been probed and the effective magnetization values have been extracted. Weak in-plane anisotropies observed for the Co₂MnGe sample indicate a textured growth of the films. Non-uniform (spin-wave and interface/surface) modes have been observed and the exchange stiffness constants for the Co₂MnSn and Co₂MnGe films have been estimated.

Multistacked Ge quantum dots (QDs) with Si spacers of different thicknesses have been grown on (100) Si substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and post-annealing. The presence of a ferromagnetic structure was confirmed in the insulating (Si_0.45Ge_0.55)Mn_0.03 diluted magnetic quantum dots (DMQD) and semiconducting (Si_0.45Ge_0.55)Mn_0.05 DMQD. The DMQD materials were found to be homogeneous, and to exhibit p-type conductivity and ferromagnetic ordering with Curie temperatures T_C = 350 and 160 K respectively. The x-ray diffraction (XRD) data show that there is a phase separation of Mn₅Ge₃ from the MnGe nanostructure. Temperature-dependent electrical resistivity in the semiconducting DMQD material indicates that manganese introduces two acceptor levels in germanium at 0.14 eV from the valence band and 0.41 eV from the conduction band implying that Mn substitutes for Ge. Therefore, it is likely that the ferromagnetic exchange coupling of DMQD material with T_C = 160 K is hole-mediated due to formation of bound magnetic polarons and the ferromagnetism in the sample with T_C > 300 K is due to Mn₅Ge₃ phase.

Superconductivity in carbon nanotubes (CNTs) is attracting considerable attention. Recently, we have reported successful boron doping into single-walled CNTs (SWNTs) and also revealed its correlation with superconductivity. In the present study, we report results of pressure-applied magnetization measurements in films consisting of ropes of boron-doped SWNTs. It reveals that Tc and magnitude for Meissner effect is mostly independent of applied pressure, while magnitude of graphite diamagnetism drastically increases as pressure increases. We also report result of resistance measurements in the samples and also correlation of boron doped SWNTs with multi-walled CNTs, in which we reported superconductivity previously.