Table of contents

The 13th International Conference on Muon Spin Rotation, Relaxation and Resonance (μSR2014) organized by the Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute in collaboration with the University of Zurich and the University of Fribourg, was held in Grindelwald, Switzerland from 1st to 6th June 2014. The conference provided a forum for researchers from around the world with interests in the applications of μSR to study a wide range of topics including condensed matter physics, materials and molecular sciences, chemistry and biology. Polarized muons provide a unique and versatile probe of matter, enabling studies at the atomic level of electronic structure and dynamics in a wide range of systems. The conference was the thirteenth in a series, which began in Rorschach in 1978 and it took place for the third time in Switzerland. The previous conferences were held in Cancun, Mexico (2011), Tsukuba, Japan (2008), Oxford, UK (2005), Williamsburg, USA (2002), Les Diablerets, Switzerland (1999), Nikko, Japan (1996), Maui, USA (1993), Oxford, UK (1990), Uppsala, Sweden (1986), Shimoda, Japan (1983), Vancouver, Canada (1980), and Rorschach, Switzerland (1978).

These conference proceedings contain 67 refereed publications from presentations covering magnetism, superconductivity, chemistry, semiconductors, biophysics and techniques. The conference logo, displayed in the front pages of these proceedings, represents both the location of μSR2014 in the Alps and the muon–spin rotation technique. The silhouette represents the famous local mountains Eiger, Mönch and Jungfrau as drawn by the Swiss painter Ferdinand Hodler and the apple with arrow is at the same time a citation of the Wilhelm Tell legend and a remembrance of the key role played by the muon spin and the asymmetric muon decay (which for the highest positron energy has an apple like shape). More than 160 participants (including 32 registered as students and 13 as accompanying persons) from 19 countries submitted 227 contributions, which were intensively discussed during day and evening sessions. The scientific program was centered around invited talks from speakers outside the μSR community, who presented lectures on topics where μSR is giving or expected to give significant contributions. The invited speakers, covering various fields of interest, included Radu Coldea (Oxford, Quantum Magnetism), Claude- Henri Delmas (Bordeaux, Electro- and Solid State Chemistry), Dirk Johrendt (Munich, Iron Based Materials), Marc-Henri Julien (Grenoble, Cuprate Superconductors), Manfred Fiebig (Zürich, Multiferroics), Allan MacDonald (Austin, Topological Electronic States), Hidenori Takagi (Stuttgart and Tokyo, Transition Metal Oxides), and Jean-Marc Triscone (Geneva, Oxide Heterostructures). In addition to an overview about status and progress of the existing facilities in Europe, Canada and Japan, future projects and new ideas for μSR facilities in South Korea, China and the USA were presented. A special evening session was held to discuss about muon site and muon states calculations by DFT and other techniques. Several talks and posters can be found on the conference web page www.psi.ch/muSR2014.

In a ceremony at the beginning of the conference, Roberto De Renzi from the University of Parma was awarded the 2014 Yamazaki Prize for muon science by the International Society for Muon Spin Spectroscopy (ISMS) for his sustained and exceptional contributions to the development of the muon spin relaxation technique to investigate magnetism and superconductivity and for promoting synergies between μSR and NMR. In the closing session Rob Kie (UBC Vancouver and TRIUMF) very effectively summarized the five days of meeting, while giving an enlightening personal impression. In the same session five best poster prizes were awarded and ISMS gave two prizes to young researchers presenting outstanding work at the conference. The conference organizers also on behalf of the entire μSR community are extremely grateful to the conference sponsors: PSI, University of Zürich, University of Fribourg and the Swiss National Foundation as well as to the various industrial sponsors, which are listed in these proceedings. Special mention should also be made of the local organizing committee who has been active during a long period first preparing and then running the conference. Finally we would like to thank the participants whose stimulating research presentations and lively discussion made μSR2014 such a success.

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.

We present a preliminary report of zero and transverse field μSR measurements in a high quality single crystal of fully oxygenated Sr₃Fe₂O₇[1], the insulating 3d magnetic analogue of the well studied Sr₃Ru₂O₇, in its charge-disproportionated state, through the magnetic transition to the incommensurate phase at T_N ~ 115 K. A very broad distribution of static fields below T_n yields a large (2/3) missing fraction. Rapidly damped zero field oscillations indicate a large internal field at the muon, estimated to be 0.46 T at 0 K. In the paramagnetic state, we find two muon precession frequencies at 0.25 T applied field, reminiscent of the Mössbauer spectra.

We report on the muon Knight shift in a polycrystalline sample of Y_0.95Sc_0.05Mn₂ that is known as one of the d-electron heavy fermion compounds. Since the muon site is presumed to have a trigonal symmetry, it is expected that the Fourier-transformed (FT) spectrum line shape would exhibit a uni-axial powder pattern which has two edges determined by the parallel and perpendicular components of the Knight shift, K_|| and K_⊥, where K_|| (K_⊥) is proportional to the parallel (perpendicular) component of the spin susceptibility, χ_|| (χ_⊥). The observed FT spectrum at 2 K largely disagrees with the calculated line shape in isotropic (χ_|| = χ_⊥) and anisotropic (χ_|| ≠ χ_⊥) cases, suggesting that there must be field- induced staggered magnetization due to strong antiferromagnetic spin correlations.

Zero (ZF) and longitudinal field (LF) muon spin relaxation data of the d-metal alloy Ni_1-xV_x are presented at several vanadium concentrations x below and above the critical x_c ≈ 11 % where long-range ferromagnetic (FM) order is suppressed. The clear single precession frequency observed for Ni, as expected for a homogeneous FM, changes to rather damped osciallation with small V substitution at x = 4 %, confirming magnetic inhomogeneities caused by the less magnetic V environments in the magnetic Ni matrix. Furthermore, local fields and spatial field distributions can be estimated to characterize different inhomogeneous regimes developing with x in the FM phase of Ni_1-xV_x. In the regime of x = 7 – 10 % a Kubo Toyabe function well describes the low temperature ZF and LF asymmetry data supporting a static Gaussian field distribution. Closer to the quantum critical concentration a single scale static Kubo Toyabe function with one field distribution is not sufficient to describe the muon relaxation. These data indicate that further changes in spatial distributions and dynamics are evolving as expected within the critical regime of a disordered quantum critical point.

We present a detailed μSR study of the recently synthesized compound, [NH₄]₂[C₇H₁₄N][V₇O₆F₁₈] (DQVOF), a geometrically frustrated magnetic material, both in longitudinal and transverse configurations. The μSR measurements in zero and longitudinal field show that there is no spin freezing down to 20 mK which is the key requirement for a quantum spin liquid state. Further experiments in transverse field single out two contributions with different shift and broadening which shed a new light on the location of the muons stopping sites.

Whenever a compound exhibits a spontaneous μSR oscillation, long-range magnetic ordering is usually inferred. Here we show that some caution is required. The coherence length needs not to be large for a spontaneous muon spin precession to be observed. Establishing the incommensurate nature of a magnetic structure, solely based on μSR measurements, may not be reliable. The absence of a spontaneous muon precession at low temperature does not mean that the system under investigation does not display long-range magnetic ordering.

The relaxation measured in zero and longitudinal field in the quasi-static limit is usually analyzed in the framework of the strong-collision model, the static polarization function being taken to be the famous Kubo-Toyabe function. This might not be satisfactory if short-range correlation effects are strong. Here we propose a method based on the maximum entropy concept and reverse Monte Carlo technique which gives results consistent with those obtained in 2013 by analytical means for the considered example.

We report muon spin rotation/relaxation measurements of muonium in mesoporous silica (SBA-15) with a high specific surface area of 600 m²/g. Up to 70 percent of the incoming muons form muonium and escape efficiently into the open pores at all temperatures between 3 and 300K. We present evidence that the interaction with the silica surfaces involves both spin exchange and a transition to a diamagnetic state, possibly due to dangling bonds on the surface. At very low temperatures, below 20K, the interaction between muonium and the silica surfaces is suppressed due to a He film coating the surfaces. These results indicate that it should be possible to use muonium to probe the surfaces of uncapped nanoparticles supported in silica.

The quantum spin dimer system NH₄CuCl₃ has a gapless ground state with T_N = 1.3 K, and shows plateaus in the high-field magnetization at 1/4 and 3/4 of the saturation magnetization, the mechanism of which has not yet been resolved until now. The three dimer model recently proposed by Matsumoto, which seems well accounting for the emergence of plateaus, predicts the existence of three magnetically-inequivalent dimers. In order to test the model, we have measured transverse-field (TF) muon depolarization curves. In fourier transform of TF muon depolarization curves, we observed homogeneous single peak at T > 100 K. Below 70 K, the peak showed rapid broadening, and split into multiple peaks in still lower temperatures, supporting the idea of the three dimer subsystems.

Although stoichiometric lithium cobalt dioxide LiCoO₂ (ST-LCO) is the most common positive electrode material for Li-ion batteries, the magnetic nature of ST-LCO is still not fully understood. Therefore, we measured susceptibility (χ), electron paramagnetic resonance (EPR), and μSR for ST-LCO, particularly above 100 K. The temperature dependence of χ shows a Pauli paramagnetic behavior, supporting the previous conclusion that Co³⁺ ions are in a low-spin state with S = 0 (t⁶_2g). However, the EPR and μSR measurements reveal a "dynamical" magnetic phase in ST-LCO above 100 K. Because the volume fraction of this magnetic phase reaches about 50% at 300 K, the appearance of the magnetic phase is not caused by impurities and/or muonium formation but is an intrinsic characteristic of ST-LCO. By considering the time windows of the three measurement techniques used in this study, we conclude that the origin of the dynamical magnetism is most likely spin fluctuations of the Co ions.

In order to investigate the diffusive motion of Li⁺ in a thin film electrode material for Li-ion batteries, we have measured β-NMR spectra of ⁸Li⁺ ions implanted into epitaxial films of Li_0.7CoO₂ and LiCoO₂ in the temperature range between 10 and 310 K. Below 100 K, the spin-lattice relaxation rate (1/T₁) in the Li_0.7CoO₂ film increased with decreasing temperature, indicating the appearance and evolution of localized magnetic moments, as observed with μ⁺SR. As temperature is increased from 100 K, 1/T₁ starts to increase above ~ 200 K, where both Li- NMR and μ⁺SR also sensed an increase in 1/T₁ due to Li-diffusion. Interestingly, such diffusive behavior was found to depend on the implantation energy, possibly because the surface of the film is decomposed due to chemical instability of the Li_0.7CoO₂ phase in air. Such diffusive behavior was not observed for the LiCoO₂ film up to 310 K.

In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-μ⁺SR spectra for the Sr_1-xCa_xCo₂P₂ powder samples with x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1. Due to a characteristic time window and spatial resolution of μ⁺SR, the obtained phase diagram was found to be rather different from that determined by magnetization measurements. That is, as x increases from 0, a Pauli-paramagnetic phase is observed even at the lowest T measured (1.8 K) until x = 0.4, then, a spin-glass like phase appears at 0.5 ≤ x ≤ 0.6, and then, a phase with wide field distribution probably due to incommensurate AF order is detected for x = 0.8, and finally, a commensurate A-type AF ordered phase (for x = 1) is stabilized below T_N ~ 80 K. Such change is most likely reasonable and connected to the shrink of the c-axis length with x, which naturally enhances the magnetic interaction between the two adjacent Co planes.

In order to elucidate the magnetic nature of K₂NiF₄-type 3d transition metal oxides, we have measured μ⁺SR spectra for Sr₂VO₄, LaSrVO₄, and Sr₂CrO₄ using powder samples. ZF- and wTF-μ⁺SR measurements propose that Sr₂VO₄ enters into the static antiferromagnetic (AF) order phase below 8 K. In addition, TF-μ⁺SR measurements evidence that the transition at 105 K is not magnetic but structural and/or electronic in origin. For LaSrVO₄, static long-range order has not been observed down to 20 K, while, as T decreases from 145 K, wTF asymmetry starts to decrease below 60 K, suggesting the appearance and evolution of localized magnetic moments below 60 K. For Sr₂CrO₄, by contrast, both ZF- and wTF-μ⁺SR have confirmed the presence of antiferromagnetic order below 117 K, as predicted in the χ(T) curve.

In order to investigate the microscopic magnetic nature of a sodium phospho- olivine, we have measured μ⁺SR spectra for Na_xFePO₄ using a powder sample in the temperature range between 2 and 500 K. ZF-μ⁺ SR measurements below 200 K at TRIUMF showed the appearance of static magnetic order below T_N ~ 61 K, where the susceptibility-vs.- temperature curve exhibits a sharp maximum due to an antiferromagnetic (AF) transition. The wide distribution found for the internal magnetic field (H_int) was explained by the formation of AF order with the spread in H_int due to random distribution of Na vacancies. At higher temperatures, the ZF-spectrum for Na_0.7FePO₄, obtained at J-PARC, is found to change from a low-T static behavior to a high-T dynamic behavior above ~ 300 K. This is consistent with the fact that Na⁺ ions are reversibly extracted from and intercalated into the NaxFePO4 lattice, while there is no NMR study on Na-diffusion in Na_xFePO₄ due to large Fe moments.

In order to elucidate the magnetic nature for a novel one-dimensional zigzag chain compound, NaCr₂O₄, we have measured μ⁺SR spectra using a powder sample in the temperature range between 2 and 200 K. Weak transverse field (wTF-) μ⁺SR measurements indicated that the whole volume of the sample enters into an antiferromagnetic (AF) phase below T_N = 125 K. The zero field (ZF-) μ⁺SR spectrum obtained below T_N exhibits a clear oscillation with a single muon-spin precession frequency (fμ). This suggests that static AF order is formed below T_N and that all the implanted muons sense the same internal magnetic field. The temperature dependence of fμ was found to be very similar to that for the intensity of the magnetic Bragg peak in neutron diffraction (ND) measurements. On the other hand, the ZF-μ⁺SR spectrum for the isostructural compound, β-CaCr₂O₄, showed a rapidly damped oscillation below T_N = 21 K, supporting the formation of incommensurate AF order, as proposed by ND.

Magnetic properties of multiferroic Eu_1-xY_xMnO₃ with x = 0.2, 0.3 were studied by μSR and Mossbauer spectroscopy. Both compounds are known to become antiferromagnetic with Mn³⁺ being the only magnetic ion. We find T_N = 47±0.5K for x = 0.2 and 45±0.5K for x = 0.3. Below T_N three different magnetic states (AFM-1, AFM-2, AFM-3) are formed. The μSR parameters of the uppermost magnetic state (AFM-1) are alike in both compounds, and compatible with a commensurate modulated collinear spin structure. The magnetic ground state in x = 0.2 (AFM-3) is shown to be single phase. Its spectral parameters support the proposal of a cone-like spin structure, yet with incommensurate modulation. The ground state for x = 0.3 is found to have an incommensurate spiral spin structure. ¹⁵¹Eu Mössbauer spectroscopy measured the Eu hyperfine field induced by the Mn³+ ions. Its low value (~4T) means that mixing with higher Eu electronic states is small and that the Mn-Eu exchange coupling is weak (~0.5K). The various magnetic transitions appear as small irregularities in the temperature dependence of the hyperfine fields. The present results are discussed in terms of different published magnetic phase diagrams of Eu_1-xY_xMnO₃.

The metallic ruthenium perovskites ACu₃Ru₄O₁₂ with A = Ca, Pr,Nd were investigated by zero field (ZF) and weak transverse field (TF) muon spin rotation/relaxation (μSR) spectroscopy. The ZF spectra for CaCu₃Ru₄O₁₂ show pure static Gaussian Kubo-Toyabe relaxation arising from the interaction between the muon spin and the nuclear moments of the Cu ions. This confirms that no atomic magnetic moment exists. A sudden increase of the lattice parameter a when heating above ~150 K had previously been detected by neutron diffraction. The root mean square field at the muon site B_rms was found to be 0.15 mT independent of temperature, in particular around 150 K. Also, no change of spectral parameters is seen in the weak TF data in that temperature range. Those findings imply that the structural change around 150 K takes place without noticeably shifting atomic positions. The spectra for PrCu₃Ru₄O₁₂ and NdCu₃Ru₄O₁₂ are dominated by the interaction with the dynamic rare earth moments. The analysis requires the use of the electron-nuclear double relaxation formalism. The electronic part shows simple exponential relaxation typical for a paramagnet. It features, with reducing the temperature a steep increase of paramagnetic relaxation rate as is characteristic for an approach to a magnetic spin freezing transition from above. That result suggests that the magnetic ground states of PrCu₃Ru₄O₁₂ and NdCu₃Ru₄O₁₂ are spin frozen states, although bulk magnetic data give no direct evidence in that direction.

It has long been believed that coexistence among ferromagnetic ordering, superconductivity or heavy-fermion behaviour is impossible, as the former supports parallel spin alignment while the latter two phenomena assume a spin-singlet configuration. This understanding has recently been challenged by a number of observations in uranium intermetallic systems where superconductivity (SC) is found within a ferromagnetic state and both ordering phenomena are facilitated by the same set of comparatively heavy quasiparticles which bind into spin-triplet pairs in the SC state. Within the heavy-fermion scenario, this mechanism necessarily assumes that the magnetism has a band character. This band is expected to be responsible for all three phenomena – heavy-fermion behaviour, ferromagnetism and superconductivity – although its nature and the nature of the heavy quasiparticles have so far remained unclear. Our high-field muon spin rotation measurements are indicative of spin polarons of subnanometer size in UGe₂. These spin polarons behave as heavy quasiparticles made of 5f electrons. Once coherence is established, they may form a narrow spin-polaron band which thus may provide a natural reconciliation of itinerant ferromagnetism with spin-triplet superconductivity and heavy-fermion behaviour.

We report the first transverse, longitudinal and zero field measurements performed on Vanadium Dioxide (VO₂) where we find a significant local magnetic field below T = 34.7 ± 0.16 K at the muon site and Mu_d motion above 340 K. Distinct shifts in the muon relaxation rates and Kubo-Toyabe delta parameters, near the metal to semiconductor and structural transition (T_MST ≈ 340 K), show that μ⁺SR measurements may provide additional means to further characterize the mechanisms contributing to these transitions that are yet to be understood.

The Laves phase intermetallics REAl₂ were studied by μSR over several decades. Results had mainly been obtained for the temperature and field dependencies of relaxation rates in the paramagnetic state. However, it turned out that spontaneous precession signals in the ordered magnetic state were very difficult to observe. We report here the observation a weak precession signal in a single crystalline sample of DyAl₂. The precession signal seen has low asymmetry and is heavily damped. This is understood with the notion that the magnetic structure of DyAl₂ splits the internal field at the interstitial muon stopping site into several components, and that of those only one of the field components leads to the visible precession signal. The observed temperature dependence of the precession frequency is compatible with the change of easy axis of magnetization at T = 40K.

It is shown in a new class of pyrochlore compound YMn₂Zn_20-xIn_x (with x = 2.36) that the spin fluctuation rate (v) is proportional to temperature (v ∝ T) below T₀ ~10 K where heavy-fermion(HF)-like behavior is observed. Such a linear T dependence, commonly found in Y(Sc)Mn₂ and LiV₂O₄, is expected for intersecting quasi-1D Hubbard chains, suggesting that the quasi-1D character of the t_2g band associated with the pyrochlore lattice plays an important role in the emergence of the HF-like state, where T₀ may correspond to intra-chain antiferromagnetic interaction energy between Mn spins.

We present resistivity, magnetization, and zero field muon spin relaxation (μSR) data for the pyrochlore iridate materials Nd_2-xCa_xIr₂O₇ (x = 0, 0.06, and 0.10) and Sm₂Ir₂O₇. While Nd₂Ir₂O₇ (Nd227) is weakly conducting, Sm₂Ir₂O₇ (Sm227) has a slowly diverging resistivity at low temperature. Nd227 and Sm227 exhibit magnetic anomalies at T_M = 105K and 137K, respectively. However, zero-field μSR measurements show that long-range magnetic order of the Ir⁴⁺ sublattice sets in at much lower temperatures (T_LRO ~ 8K for Nd227 and 70K for Sm227); both materials show heavily damped muon precession with a characteristic frequency near 9 MHz. The magnetic anomaly at T_M in Nd227 is not significantly affected by the introduction of hole carriers by Ca-substitution in the conducting Nd_2-xCa_xIr₂O₇ samples, but the muon precession is fully suppressed for both.

We report synchrotron radiation diffraction and muon spin rotation (μSR) measurements on the frustrated pyrochlore magnet Tb₂Ti₂O₇. The powder diffraction study of a crushed crystal fragment does not reveal any structural change down to 4 K. The μSR measurements performed at 20 mK on a mosaic of single crystals with an external magnetic field applied along a three-fold axis are consistent with published a.c. magnetic-susceptibility measurements at 16 mK. While an inflection point could be present around an internal field intensity slightly above 0.3 T, the data barely support the presence of a magnetization plateau.

Certain magnetic materials may contain spin polarons (SP) – tiny, stable ferromagnetic "droplets" in a paramagnetic or weakly ordered "sea" of more random spins. The positive muon may become associated with SP, giving a unique window on their properties. In this experiment the μ⁺SR spectroscopy of "avoided level crossing resonance" (μALCR) was used on several candidate materials to further explore this model. The results leave many questions unanswered.

Low temperature growth methods were used to encapsulate a buried Mn δ-doping layer into a silicon host. A β-NMR investigation was performed of the magnetic properties in the temperature range 10 – 300 K using spin-polarized ⁸Li⁺. A depth-dependent broadening and shift of the NMR resonance was detected that is consistent with internal fields distributed at depths of 10 – 30 nm beneath the surface. At low temperatures, a negative relative shift occurred and the resonance was significantly broadened. At 300 K the line-shape could be described by a single Gaussian line, however, at 10 K the line is best approximated by a two component Lorentzian shape consisting of a broad and narrow component as anticipated for a diluted magnetic alloy. The overall magnitude of the resonance shift at both temperatures is small suggesting a weak interaction between the ⁸Li⁺ and the magnetic Mn environment.

The origin of a pseudogap in the underdoped phase of cuprates has become one of the leading issues in understanding the mechanism(s) of high-T_c superconductivity. Several experiments (i.e. polarized neutron diffraction studies) support theoretical models based on the circulating current (CC) picture. These CC models suggest a novel ordered phase formed by orbital magnetic moments caused by spontaneous orbital currents. However to date, μSR experiments in cuprate superconductors have not revealed any magnetic field higher than 0.2 G associated with orbital moments. Here we present high magnetic field μSR spectroscopy of a stoichiometric La₂CuO₄ crystal which shows antiferromagnetic splittings and additional 45 G line splittings, consistent with orbital currents.

We present our results of a local probe study on EuFe₂(As_1-xP_x)₂ single crystals with x=0.13, 0.19 and 0.28 by means of muon spin rotation and ⁵⁷Fe Mössbauer spectroscopy. We focus our discussion on the sample with x=0.19 viz. at the optimal substitution level, where bulk superconductivity (T_SC = 28 K) sets in above static europium order (T^Eu = 20 K) but well below the onset of the iron antiferromagnetic (AFM) transition (~100 K). We find enhanced spin dynamics in the Fe sublattice closely above T_SC and propose that these are related to enhanced Eu fluctuations due to the evident coupling of both sublattices observed in our experiments.

Due to its anticuprate Ti₂O layer and its fascinating phase diagram with a large coexistence area of superconductivity and a density wave phase, the new class of titanium based superconductors attracts great scientific interest. In this paper we report μSR investigation on powder samples of Ba_1-xNa_xTi₂Sb₂O (x = 0, 0.15, 0.25). Our results exhibit both the presence of a charge density wave and superconductivity in Ba_1-xNa_xTi₂Sb₂O. The superconducting order parameter, extracted from a vortex state analysis using the numeric Ginzburg-Landau model, is compatible with a s-wave symmetry. In the universal Uemura classification of superconductors this compound is at the verge of unconventional superconductivity.

We have performed muon spin rotation/relaxation and ¹¹⁹Sn nuclear magnetic resonance (NMR) measurements to study the vortex state of polycrystalline samples of YPd₂Sn (T_c = 5.4 K), over a wide range of applied magnetic fields up to B_c2(T). Measurements in the vortex state provide the temperature dependence of the effective magnetic penetration depth λ(T) and the field dependence of the superconducting gap Δ(0). The results are consistent with a very dirty s-wave BCS superconductor with λ(0) = 212(1) nm, a gap Δ(0) = 0.85(3) meV, and a Ginzburg-Landau coherence length ξ_GL(0) ≊ 23 nm. The μSR data in a broad range of applied fields are well reproduced by taking into account a field-related reduction of the effective superconducting gap. Interestingly, the ratio 2Δ(0)/(k_BT_c) appears to a good approximation to be field-independent, with a value at low field of 3.85(9), implying a field dependence of the gap . We discuss the significance of this result.

The low-temperature microscopic magnetic properties of the quasi-2D heavy- fermion compound, CePt₂In₇ are investigated by using a positive muon-spin rotation and relaxation (μ⁺SR) technique. Clear evidence for the formation of a commensurate antiferromagnetic order below T_N ≈ 5.40 K is presented. The magnetic order parameter is shown to fit well to a modified BCS gap-energy function in a strong-coupling scenario.

Muon spin relaxation and rotation (μSR) measurements have been performed to study the superconducting properties of Ca₃Ir₄Sn₁₃. Zero-field μSR data shows no sign of any magnetic anomaly in Ca₃Ir₄Sn₁₃ at the superlattice transition temperature, T^* or in the superconducting ground state. Transverse-field μSR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth λ. The dependence of λ⁻² with temperature is consistent with the existence of a single s-wave energy gap in the superconducting state of Ca₃Ir₄Sn₁₃ with a gap value of 1.51(5) meV at absolute zero temperature. The magnetic penetration depth at zero temperature λ(0) is 351(4) nm. The ratio Δ(0)/k_BT_c = 2.41(8) indicates that Ca₃Ir₄Sn₁₃ is a strong-coupling superconductor.

Encouraged by predictions of simple Fermi liquid behavior in the overdoped versions of high temperature superconductors (HT_cSC) based on CuO₂ planes, we have performed TF-μ⁺ SR experiments on several high quality oriented crystal mosaics of Tl₂Ba₂CuO_6+x ("Tl-2201") in the vortex-lattice state where the magnetic penetration depth λ can be extracted from the characteristic superconducting (SC) lineshape by χ²-minimization fitting in the time domain. The results show evidence for a surprising degree of disorder, causing some "smearing" of the characteristic lineshape features, but we were able to extract λ as a function of temperature, revealing a remarkably consistent T-dependence of the SC carrier density n_s ∝ λ⁻² that suggests this "role-model cuprate" is anything but "simple". The extracted superfluid density for all dopings exhibits a clear inflection point with temperature, suggesting a vortex lattice transition. Such a transition would have important implications for other measurements.

Zero-field muon spin relaxation measurements were carried out with Al-0.67%Mg- 0.77%Si alloys in the temperature range from 20 K to 300 K. Observed relaxation spectra were compared with the relaxation functions calculated by a Monte Carlo simulation with four fitting parameters: the dipolar width, trapping rate, detrapping rate and fraction of initially trapped muons. From the fitting, the temperature variations of the trapping rates reveal that there are three temperature regions concerning muon kinetics. In the low temperature region below 120 K, muons appeared to be trapped in a shallow potential yielded by dissolved Mg atoms, and thus little effect of heat treatment of the samples was observed, while in the mid and high temperature regions, the trapping rates clearly depended on the heat treatment of the samples suggesting muon-cluster and/or muon-vacancy interactions.

We report preliminary low-energy β-NMR measurements of ⁸Li⁺ implanted in single crystal rutile TiO₂ at an applied field of 6.55 T and 300 K. We observe a broad 12 kHz wide quadrupole split resonance with unresolved features and a sharp component at the Larmor frequency. The line broadening may be caused by overlapping multi-quantum transitions or motion of ⁸Li⁺ on the scale of its lifetime (1.21 s). We also find spin-lattice relaxation that is relatively fast compared to other wide band gap insulators. The origin of this fast relaxation is also likely quadrupolar and may be due to anisotropic ⁸Li⁺ diffusion.

We present extensive high magnetic field β-NMR measurements of ⁸Li⁺ implanted in single crystals of MgO. The narrow resonance, consistent with a cubic ⁸Li⁺ site, likely the tetrahedral interstitital, is used routinely as a reference for shift measurements. We show the intrinsic linewidth is on the order of 200 Hz, allowing a frequency determination to an accuracy of a few Hz. We find no implantation energy dependence of the resonance within a few ppm, but there is evidence of slow spin dynamics in hole-burning measurements. The spin lattice relaxation is slow. The temperature dependence reveals interesting changes at low temperature whose origin remains uncertain.

We report detailed behaviour of low energy ⁸Li implanted near the surface of α- Al₂O₃ single crystal, as revealed by beta-detected NQR of ⁸Li. We find that the implanted ⁸Li occupies at least two sites with non-cubic symmetry in the Al₂O₃ lattice. In both sites the ⁸Li experiences axially symmetric electric field gradient, with the main principal axis along the c-crystallographic direction. The temperature and field dependence of the spin lattice relaxation of ⁸Li in α-Al₂O₃, indicate that the ⁸Li diffusion is negligible on the scale of its lifetime, 1.21 s.

We have used the pulsed muon source at ISIS to study high-temperature Na-ion dynamics in the quasi-one-dimensional (Q1D) metallic antiferromagnet NaV₂O₄. By performing systematic zero-field and longitudinal-field measurements as a function of temperature we clearly distinguish that the hopping rate increases exponentially above T_diff ≈ 250 K. The data is well fitted to an Arrhenius type equation typical for a diffusion process, showing that the Na-ions starts to be mobile above T_diff. Such results make this compound very interesting for the tuning of Q1D magnetism using atomic-scale ion-texturing through the periodic potential from ordered Na-vacancies. Further, it also opens the door to possible use of NaV₂O₄ and related compounds in energy related applications.

In order to clarify the reason why the hydrogen desorption temperature (T_d) of MgH₂ is lowered by milling, we have studied the change in a local nuclear magnetic field with temperature by means of μ⁺SR. We have found a very clear oscillation in the ZF-spectrum at 2 K for the "milled" and "milled with Nb₂O₅" samples, while such oscillation is weaker for the "as prepared" MgH₂. It was also found that the oscillation signal is stable up to 250 K and is assigned mainly due to the formation of a H-μ-H system. At temperatures above ambient T, we also found that the ZF-μ⁺SR spectrum exhibits a static Kubo-Toyabe behavior due to the nuclear magnetic field of ¹H. Furthermore, it was clarified that rapid H diffusion starts well below T_d only in the milled samples, leading to the conclusion that the consequent enhanced diffusion rate in MgH₂ is essential to accelerate the desorption reaction and to decrease T_d.

We have studied low-temperature magnetic properties as well as high-temperature lithium ion diffusion in the battery cathode materials Li_xNi_1/3Co_1/3Mn_1/3O₂ by the use of muon spin rotation/relaxation. Our data reveal that the samples enter into a 2D spin-glass state below T_SG ≈ 12 K. We further show that lithium diffusion channels become active for T ≥ T_diff ~ 125 K where the Li-ion hopping-rate [v(T)] starts to increase exponentially. Further, v(T) is found to fit very well to an Arrhenius type equation and the activation energy for the diffusion process is extracted as E_a ≈ 100 meV.

Polyether ether ketone (PEEK) is a thermoplastic polymer with a wide range of applications due to its chemical inertness and thermal stability, and for these reasons sample cells for gas and liquid phase μSR have been constructed from PEEK. Muon levelcrossing resonance (μLCR) studies of PEEK revealed a broad, strong μLCR signal that, we hypothesize, is due to multiple overlapping resonances from the various muonium (Mu) adducts of PEEK. To investigate this, two monomer units from PEEK (4,4'-dihydroxybenzophenone and para-dimethoxybenzene) were studied in solution using transverse-field muon spin rotation (TF-μSR) and μLCR. Two different muoniated radicals were formed by Mu addition to 4,4^/- dihydroxybenzophenone and one radical was formed in para-dimethoxybenzene. The μSR spectra were assigned by comparing the experimentally measured muon and proton hyperfine coupling constants with values calculated for the possible structures using Gaussian-09 software with the B3LYP functional and 6-31G basis set. Good agreement was found for cyclohexadienyl- type radicals formed by Mu addition to the benzene rings of the monomer units. We can also infer that these radicals are being formed in PEEK, and based on this we conclude that sample cells made of PEEK are unsuitable for many types of μSR experiment.

Unlike the positive muon, we expect the chemistry of the implanted ⁸Li⁺β-NMR probe in organic polymers to be simply that of the monovalent ion, but almost nothing is known about the NMR of isolated Li+ in this context. Here, we present a brief survey of ⁸Li⁺β-NMR in a variety of insulating polymers at high magnetic field, including polyimide, PET, polycarbonate, polystyrene and polyethylene oxide. In all cases, we find a large-amplitude, broad Lorentzian resonance near the Larmor frequency, consistent with the expected diamagnetic charge state. We also find remarkably fast spin-lattice relaxation rates 1/T₁. There is very little dependence of either linewidth or 1/T₁ on the proton density, the main source of nuclear dipolar magnetic fields, leading us to conclude the main contribution to both broadening and spin relaxation at room temperature is quadrupolar in origin. This behaviour is very different from crystalline insulators such as MgO and Al₂O₃, and suggests that ⁸Li⁺β-NMR will be an important probe of polymer dynamics. Additionally, we note dramatically different behaviour of one sample above its glass transition, motivating the construction of a high temperature spectrometer to enable further exploration at elevated temperature.

We present results of longitudinal field repolarisation measurements carried out at J-PARC and ISIS on the "green" functional carbon materials Starbon 300 and Starbon 800, synthesized using starch as a template and subjected to pyrolysis treatments at different temperatures (300°C and 800°C respectively); pyrolysis at low temperature may be expected to yield a material retaining more of the "hydrophilic" properties of the original starch material in its chemically active voids, while high temperature pyrolysis may be expected to lead to "hydrophobic" voids and a more graphitic material. The hydrophilic material shows a larger repolarising fraction than the hydrophobic material, with a hyperfine constant on the order of 200-300 MHz. This is likely to be a superposition of the repolarisation of multiple radicals. Several candidate and model species are investigated through accompanying density functional theory calculations.

Longitudinal field muon spin relaxation (LF-μSR) has been used to measure the magnetic field dependence of the longitudinal field muon spin relaxation rates (λ_μ = 1/T^μ₁) of two muoniated radicals, 2-muoxyprop-2-yl radical (formed by Mu addition to acetone) and the muoniated 1,2-dicarboxyvinyl radical dianion (formed by Mu addition to the 1,2- dicarboxyacetylene dianion), in aqueous solution. The rotational correlations time of the radicals in solution at 298 K were determined from the magnetic field dependence of λ_μ and were found to be 32±2 ps for the 2-muoxyprop-2-yl radical and 55±3 ps for the muoniated 1,2-dicarboxyvinyl radical dianion.

We report the hyperfine coupling constants of muoniated radicals formed in a number of organic semiconductors, via transverse field measurements taken in the Paschen Back limit, and compare the results to avoided level crossing resonances. Five muoniated radicals are found in tetracene, despite there only being three potential non-equivalent bonding sites, and we suggest that this might be down to crystal packing effects. For 6,13-bis(triisopropylsilylethynyl) pentacene and 6,13-bis(trimethlsilylethynyl)-pentacene, we demonstrate that the transverse field data supports the previously published avoided level crossing resonances.

Muonium (Mu), which is known to exhibit a characteristic concentration dependent spin relaxation change when impacting molecular oxygen dissolved in water, was found to show a similar behaviour in aqueous solutions of Tris Buffered Saline (TBS), albumin, serum, and hemoglobin (Hb). These effects, along with the interaction of Mu with deoxy-Hb (which is modulated by oxygen by the formation of oxy-Hb) suggest that the muon method can be applied to systematic studies of oxygen dependent effects in biological systems. This muon method may particularly be applicable at low (hypoxic) oxygen levels, an important consideration in the radiation treatment of cancer.

μSR and ALCR techniques have been used to investigate the structure and dynamics of the Mu-cyclohexadienyl radical interacting with Au and Pt metal nanoparticles (MNPs) supported in mesoporous silica (SBA-15). Surprisingly, coherent precession signals are observed and the isotropic hyperfine coupling constants are almost the same in loaded and unloaded samples, implying that the electronic structure of MuC₆H₆ is only weakly perturbed by the presence of the MNPs. We propose the observed radicals are shielded from the metallic surfaces by a benzene coating on the MNPs. The Δ₁ resonance is observable in MNP-loaded samples at higher temperatures than in the unloaded SBA-15. This is attributed to stronger binding of MuC₆H₆ to the benzene coated MNPs.

We investigated bulk and thin-film samples of the quaternary p-type semiconductor Cu₂ZnSnS₄ (CZTS) by μSR, in order to characterize the existing muonium signals. We find that the majority of the implanted muons form a diamagnetic state broadened by an interaction with the Cu nuclear moments, which we interpret as Mu⁺ bound to sulphur. A paramagnetic fraction is also present at low temperatures and the ratio between the two muon charge states, Mu⁺ and Mu⁰, varies between 20 and 40% prior to the onset of muon diffusion, which occurs at around 150 K. The fraction of Mu⁰ is found to be sensitive to the defect content of the sample. The paramagnetic fraction has two different contributions and their origin is discussed and related with the muon role as a probe for charge carriers in the material.

Polarized negative muons were used to study the behaviour of the boron acceptor centre in diamond produced by the chemical vapour deposition (CVD) method. The temperature dependence of the muon spin relaxation rate and spin precession frequency were measured in the range of 20 – 330 K in a transverse magnetic field of 14 kOe. The muon polarization amplitude P(t = 0) does not depend on the temperature and the muon spin relaxation rate decreases as the temperature increases. For the first time a negative shift of the muon spin precession was observed in diamond. The measurements show that the magnetic susceptibility of the CVD sample is negligible (χ = -4.13(2)·10⁻⁷cm³/g at 20 K) and it could not be the reason of the negative shift muon spin precession frequency. The negative shift of the muon spin precession frequency is tentatively attributed to an anisotropic hyperfine interaction in the boron acceptor in diamond.

A formation process of an acceptor center _μB induced by negative muon in a diamond crystal is considered in this work. It is shown that the process under consideration could be represented as three consecutive stages: a kinetic stage, connected with a capture of track electrons, a chemical stage, connected with establishing of chemical bounds of the radiation defect with lattice atoms, and a formation phase of the ionized negatively charged acceptor center. Quantitative estimates of characteristic times are obtained for every stage. It is shown that the total time necessary for the acceptor center formation is of the order 10⁻⁸s. So this fact should be taken into account when experimental results are interpreted.

We present high-transverse field measurements, as a function of temperature, in monoclinic ZrO₂ and HfO₂. In monoclinic zirconia and hafnia, a diamagnetic component had been previously reported in low-transverse-fields, but a significant fraction of the total muon polarization was missing in these experiments. We now characterize this missing fraction using the high-field capabilities at TRIUMF: a high relaxation component (above 100 μs⁻¹ in monoclinic ZrO₂, about 10 μs⁻¹ in HfO₂) is observed, which we relate to the formation of compact muonium in these materials. A model for the formation of muonium in these materials is presented.

It has recently been shown that at T < 270 K a persistent inversion from n- to p-type can be induced by illumination in a 200-nm-thick surface layer of lowly-doped commercial germanium wafers [1]. The presence of photo-generated holes is detected by the appearance of a fast relaxing component in TF-μSR measurements, caused by cyclic muonium charge state transitions Mu⁻_T + h⁺ ⇋ Mu⁰_T. For a quantitative determination of the photo-induced hole carrier concentration we use a Monte-Carlo simulation to generate muon decay histograms for different hole capture rates (forward reaction), and ionization rates (reverse reaction due to thermal activation) [2]. The hole carrier concentration is determined by comparing simulated and experimental relaxation rates. These results have been used to estimate the photo-induced hole concentration in low-energy μSR experiments [1].

This paper is part of an extended study of oxide materials with the μSR technique. As an example, we present here experimental data on yttria-stabilized zirconia (ZrO₂ doped with 8% Y₂O₃). Three different muon states can be distinguished: i) Deep muonium (less than 17(1)% fraction), seen as a fast-relaxing signal or indirectly via decoupling measurements in high longitudinal fields, ii) μ⁺ in a paramagnetic environment 62(6)% fraction), characterized by a very weak but clearly-visible hyperfine interaction, and iii) diamagnetic muon 21(1)% fraction); the diamagnetic signal is broadened only by the interaction with nuclear moments. The state corresponding to μ⁺ in a paramagnetic environment and the diamagnetic state are attributed to the same (oxygen-bound) muon configuration, but we assume that they have different electron surroundings (with or without an unpaired electron in the vicinity). The paramagnetic electron is not captured in the Coulomb potential of the positive muon but is self-trapped (polaron formation) at a nearby Zr ion. The distant electron interacts with the muon only via dipolar magnetic fields. This explains the very weak hyperfine interaction felt by the μ⁺ state in a paramagnetic environment. A further result of the experiment is that the disappearance of this signal with increasing temperature is not due to ionization of an electron shallowly bound to the muon but is caused by rapid spin fluctuations of the electron, averaging the hyperfine interaction to zero.

Muon positions in La₂CuO₄ were examined by using the density functional theory. Potential minimum positions near apical and plane oxygen have been determined as possible initial muon stopping positions. We found that final muon stopping positions were different from those initial positions due to effects of the local deformation of crystal structure which was induced by injected muons. This means that injected muons relax their positions deforming local crystal structures and minimizing the total energy of the system. We also found that the estimation of those final muon positions had to be done in the large scale area as a supercell which contained 27 unit cells in order to achieve realistic situations of the system with the muon as a dilute impurity.

The electrostatic potential has been investigated in YBa₂Cu₃O₆ by applying the density functional theory in order to estimate possible muon sites. We found five minimum potential positions around the apical oxygen of the CuO₅ polyhedral. In addition to those, we also found another minimum potential position near the yttrium atom which is in between the CuO₂ layers. Those estimated positions are different from those suggested from previous μSR studies on the basis of the dipole-field estimation.

Numerical investigations on muon sites in Ce-based Kondo semiconductors, Ce(Ru,Rh)₂Al₁₀ were carried out by using the Density Functional Theory. From the view point of simple electrostatic potential calculations, we found all the previously reported muon sites, suggested by different groups (Kambe S et al. 2010 J. Phys. Soc. Jpn.79 053708 and Khalyavin D D et al., 2010 Phys. Rev. B 82 100405(R)), can be possibly chosen as muon stopping sites. We also investigated the changes in the potential of the Rh-doped case. We discovered that the electronic potential around the nearest Ru atom to the substituted Rh atom is affected and the potential becomes asymmetric around the nearest Ru ion. Although big changes in hyperfine fields at muon sites have been reported (Guo H et al. 2013 Phys. Rev. B 88 115206), the muon positions estimated from the potential calculations do not change much.

The ab-initio density functional theory analysis was applied to metal-organic hybrids, (C₂H₅NH₃)₂CuCl₄ (EA) and (C₆H₅CH₂CH₂NH₃)₂CuCl₄ (PEA), in order to estimate possible muons stopping positions. Six potential minimum positions and eight ones were revealed in PA and PEA, respectively. Those potential minimum positions can be regarded as initial stopping positions of injected muons. All of expected potential minimum points in EA were near and around the apical Cl and the CuCl₂ plane of the CuCl₆ octahedra. Instead, in the case of PEA, two of eight positions were close to the phenyl ring giving a possibility that there would be muon states which couple surrounding electrons via a radical formation.

We present calculations of the dipolar field distribution acting on a single molecule magnet due to its neighbours in thin films. The calculations are presented for different packing/configuration scenarios, with different easy axis orientations. The potential for controlling the molecular spin dynamics by tuning the molecule-substrate interaction and its competition with intra-molecular interactions is discussed. We argue that by altering the configuration of the molecular moments, and thus their dipolar interactions, one can enhance or slow down their spin dynamics.

We investigate the spatial variation of the demagnetizing field for uniformly magnetized, cylindrical samples using a recently developed Fourier space approach. We show that the demagnetizing response of the sample leads to a position dependence of the magnetic field, which varies most strongly near the radial boundary of the cylinder. Furthermore, we demonstrate that the demagnetizing field leads to a subsequent broadening of the field distribution, as experienced by the muons implanted in the sample, with a characteristic shape including a low field tail and a sharp high-field cutoff. We present a detailed study of this field broadening as a function of the aspect ratio of the cylinder and find that it is significant and largest for aspect ratios typical for cylindrical samples grown in mirror furnaces. We identify two strategies to minimize this broadening: adding a degrader so that muons implant closer to the surface of the sample and using a circular mask to stop muons from implanting near the radial edge. This could help identify whether an experimentally observed broadening is caused by the demagnetization response or the intrinsic properties of the sample.

I show that the μSR technique allows one to study the occurrence of a magnetic ordering in nanocrystal films made of ferromagnetic metals – so called "scale" phase transition. The relation between the microscopic (local) field with macroscopic characteristics just as the external magnetic field, the average magnetization and the saturation magnetization is determined for a model for which the nanocrystal film consists of crystallographically ordered grains separated by disordered areas. Expressions for the behaviour of the muon spin polarization ensemble in this type of structures are obtained in cases of fast diffusing and nondiffusing muons. It is shown that experiments with "slow" positively charged muons allow one to measure all parameters of this type of structures and obtain important information for the study of phase transition physics.

Traditional muon avoided-level-crossing measurements use "integral counting" analysis, which results in a simple 1-D spectrum with resonance lines. At pulsed muon facilities, the time spectrum (TD-ALC) is available "for free" so it should be analysed to extract all relevant information. An ALC line corresponds to resonant transfer of polarisation back and forth between the muon and the other spins in a radical, and this oscillation is often at a convenient frequency of order 1 MHz. Following the oscillation frequency through just one Δm = 0 line can give the hyperfine constants for both the muon and nucleus and the gyromagnetic ratio for that nucleus.

Unlike the positive muon, β-NMR probe nuclei must be actively polarized. At the TRIUMF ISAC facility this is accomplished by in-flight collinear optical pumping with resonant circularly polarized laser light. This reliably produces a high degree of polarization, but the detailed state populations in the beam emerging from the optical polarizer are not well known. These populations are significant as they represent the initial state of the ensemble of probe spins implanted in a β-NMR experiment. Here we use the well-resolved quadrupolar split spectrum of ⁸Li⁺ in a high purity single crystal of bismuth to extract the sublevel populations under typical polarizer operating conditions, accounting for the spin relaxation in this semimetal.

I have built a "demonstration" website at http://oPeer.org to illustrate how peer review and publication might be improved relative to the current model, which was designed and implemented in an era when scientific communication was either face-to-face or relied upon human delivery of ink marks on dead trees.

The muon science facility (MUSE), along with the neutron, hadron, and neutrino facilities, is one of the experimental areas of the J-PARC project. The MUSE facility is located in the Materials and Life Science Facility (MLF), which is a building integrated to include both neutron and muon science programs. Since the autumn of 2008, users operation is effective and making use of the pulsed muon beam particularly at the D-Line. Unfortunately, MUSE suffered severe damages from the earthquake on March 11, 2011, the so-called "Higashi-Nippon Dai-Shinsai". We managed to have a stable operation of the superconducting solenoid magnet with use of the on-line refrigerator on December, 2012, although we had to overcome a lot of difficulties against components not working properly. But we had to stop again the whole operations on May 2013, because of the radioactive materials leakage accident at the Hadron Hall Experimental Facility. Finally we restarted the users' runs on February 2014.

The muon facility, J-PARC (Muon Science Establishment; MUSE), has been operating since the first beam in 2008. Starting with a 200 kW proton beam, a beam intensity of 3 × 10⁶ muons/s was reached in 2009 which was the most intense pulsed muon beam in the world. From the 2 cm thick graphite target, four secondary muon beam lines are designed to be extracted. Three beam lines currently exist, the first being operational and the other two undergoing commissioning. The fourth and the last beam line, the H line, is planned to be constructed. This new beam line is designed to have a large acceptance, provides the ability to tune the momentum, and use a kicker magnet and/or a Wien filter. The H line is designed to provide an intense beam of 10⁸ surface muons/s for fundamental physics studies to observe new physics beyond the standard model. Such studies require high statistics and they need to occupy the experimental areas for a relatively long period.

We developed a new positron detector system called Kalliope, which is based on multi-pixel avalanch photo-diode (m-APD), application specific integrated circuit (ASIC), field programmable gated array (FPGA) and ethernet-based SiTCP data transfer technology. We have manufactured a general-purpose spectrometer for muon spin relaxation (μSR) measurements, employing 40 Kalliope units (1280 channels of scintillators) installed in a 0.4 T longitudinal-field magnet. The spectrometer has been placed at D1 experimental area of J- PARC Muon Science Establishment (MUSE). Since February of 2014, the spectrometer has been used for the user programs of MUSE after a short commissioning period of one week. The data accumulation rate of the new spectrometer is 180 million positron events per hour (after taking the coincidence of two scintillators of telescopes) from a 20×20 mm sample for double-pulsed incoming muons.

Spin polarized positive muons contained in the cosmic-rays were stopped in the Fe plates providing a characteristic spin rotation signal of decay positrons. This signal along with the decay lifetime of the negative muons can be used as a non-invasive radiographic measurement method for a characterization of the inner structure of the aged architectures. Principle, results of test experiments and future prospects are described.

At the J-PARC Muon Science Facility (MUSE), a new Ultra-Slow Muon beamline is being constructed to extend the μSR technique from bulk material to thin films, thus empowering a wide variety of surface and nano-science studies, and also a novel 3D imaging with the "ultra-slow muon microscope". Ultra-slow muons will be produced by the re-acceleration of thermal muons regenerated by the laser resonant ionization of muonium atoms evaporated from a hot tungsten foil, a method that originated from the Meson Science Laboratory at KEK. The design parameters, construction status and initial beam commissioning are reported.

For μSR with ultra slow muon, we are constructing U line in materials and life science facility (MLF), J-PARC at present. Generation of ultra slow muon requires thermal muonium generation and laser resonant ionization process with vacuum ultraviolet radiation (1S→2P) and 355-nm radiation (2P→unbound). For laser resonant ionization, the coherent radiations and the thermal muonium emission must be coincident in time and space. The radiations can be steered in a chamber for reasonable overlap in space, and they can be easily overlapped in time because they are generated from one laser source. The trigger signal of the accelerator is useful for stable overlap in time.

For the last 27 years, muon experiments at ISIS have been making a significant contribution to a number of scientific fields. However, as a community of researchers, we are always aiming to improve and extend the instruments' capabilities. In this paper we will review the current significant developments at the ISIS muon facility, namely the primary beamline upgrade, proton pulse compression and the MANTID muon analysis package.