Table of contents

The International Conference on Strongly Correlated Electrons systems (SCES) is one of the most traditional conferences in Condensed Matter Physics worldwide. SCES continues to bring together, in every edition, outstanding scientists working in the frontiers of the complex and advanced phenomena of this area. The SCES 2020 Edition was planned to be an in-person event in Guaruja, SP, Brazil in September of 2020 as a continuation of the successful series of the SCES conferences: Sendai ('92), San Diego ('93), Amsterdam ('94), Goa ('95), Zurich ('96), Paris ('98), Nagano ('99), Ann Arbor ('01), Krakow ('02), Karlsruhe ('04), Vienna ('05), Houston ('07), Buzios ('08), Santa Fe ('10), Cambridge ('11), Tokyo ('13), Grenoble ('14), Hangzhou ('16), Prague ('17) and Okayama ('19). Additionally, every three years since 1997, SCES has been joining the International Conference on Magnetism (ICM) held in: Cairns ('97), Recife ('00), Rome ('03), Kyoto ('06), Karlsruhe ('09), Busan ('12), Barcelona ('15), and San Francisco ('18).

List of The international advisory committee, The prize committee, The publication Committee, The organizing committee, The local committee are available in this pdf.

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

1. Type of peer review: single blind

2. Conference submission management system: Morressier

3. Number of submissions received: 80

4. Number of submissions sent for review: 80

5. Number of submissions accepted: 73

6. Acceptance Rate (Submissions Accepted/Submissions Received × 100): 91 %

7. Average number of reviews per paper: 1

8. Total number of reviewers involved: 25

9. Contact person for queries:

Name: Eduardo Miranda

Email: emiranda@ifi.unicamp.br

Affiliation: University of Campinas - Physics

* means value has been edited

Exoticity in material properties is often linked to the complex interplay of spin, charge, orbital and lattice degrees of freedom that makes the study of the origin of such exoticity difficult. The outstanding issue is to disentangle parameter space and reveal the underlying physics. We propose a unique method to excite electrons of a selected symmetry without significant effect on other electrons using polarized pump light pulse in a pump-probe experiment. Using this technique, we show that the relaxation of itinerant electrons occurs faster than the local electrons; the first experimental identification of the orbital selective electron dynamics in a complex correlated system, EuFe₂As₂. In another experiment, we discover that the magnetic order in CaFe₂As₂ can be melted selectively without significant effect on electrons in the other energy bands. These results provide two important conclusions; (i) magnetism in Fe-based systems may not be linked to the phase space occupied by other electrons and (ii) polarized pump excitation in a pump-probe experiment is a novel method to study orbital selective dynamics.

Sr₂RuO₄ has been under intensive scrutiny over the past years after new NMR measurements unveiled that the superconducting state might be spin singlet. One of the best order parameter candidates in light of these new experiments is a chiral state with E_g symmetry. This order parameter, with a horizontal nodal line, has been overlooked given the strong two-dimensional character of the normal state electronic structure. Recently, a phenomenological proposal based on local interactions showed that an even-parity orbital-antisymmetric spin-triplet (OAST) chiral state can be stable in Sr₂RuO₄ once momentum-dependent spin-orbit coupling is properly taken into account. Here we discuss the origin of the nodes and dips in this order parameter as inherited from the normal state Hamiltonian, showing that a nodal gap can emerge out of purely local interactions and connect the presence of nodes with the superconducting fitness measure.

T'-La_1.8Eu_0.2CuO_4–yF_y (0 ≤ y ≥ 0.125) was measured by ^63,6BCu and ¹³⁹La NMR. This material is an electron-doped high-T_c cuprate superconductor which has Nd₂CuO₄-type structure (so-called T'-structure). The nuclear spin-lattice relaxation rate 1/T₁ revealed that pseudogap behavior exists in the lightly electron-doped region of y ≤ 0.075 and electron doping suppresses the antiferromagnetic spin flutuations. These behaviors in electron-doped high-T_c cuprate superconductor are analogous with the optimum- and over-doped region in hole-doped type. ¹³⁹ La NMR spectra shows almost no antiferromagnetic region in the samples of T'-La_1.8Eu_0.2CuO_4–yF_y.

We study the electronic structure of a superconducting composition of 122-type Fe-based pnictide material, CaFe_1.9Co_0.1As₂ employing high resolution angle resolved photoemission spectroscopy technique. The experimental results exhibit three bands close to Fermi level at Γ-point of the Brillouin zone among which only one band crosses the Fermi level. In the parent compound, CaFe₂As₂, all the three bands cross the Fermi level and form three hole pockets. While the destruction of Fermi pockets due to electron doping (Co-substitution dopes electrons into the system) is expected, we observe significant orbital selective band renormalization with respect to the parent compound. It appears that the effect of spin-orbit coupling is stronger in the doped compound.

We have succeeded in growing a single crystal of SrPt₃P, which was reported as a strong coupling s-wave superconductor with the critical temperature of T_c=8.4 K, and have measured the de Haas-van Alphen (dHvA) effect and the electrical resistivity under magnetic fields. Several dHvA frequency branches with the frequencies up to ~ 1 kT with the cyclotron effective masses of m_c* = 0.27 – 0.61 m₀ were observed. It was clarified that the superconducting upper critical fields _μ0H_c2 for fields along H // [001] and H // [100] in the tetragonal structure are almost the same in values of μ₀H_c2 ~4.8 T.

Single crystals of the compound Ce₃PdIn₁₁ that belongs to a large family of superconducting cerium indides with the general formula Ce_mT_nIn_3m+_2n (T stands for d-electron transition metal) were grown from indium flux and characterized by means of low-temperature specific heat and electrical resisitivity measurements. The collected data revealed significant sample-dependent divergence in their magnetic and superconducting properties which raises the question of whether these two cooperative phenomena are intrinsic properties of Ce₃PdIn₁₁.

We performed the measurements of electrical resistivity (ρ) and dc magnetization (M) as a function of temperature (T) under pressure to investigate whether or not the superconductivity is induced by the application of pressure in lightly doped RFeAsO_1-xF_x (R=Sm and Nd) using pulse current sintered (PCS) high density polycrystalline specimens. We have successfully observed pressure induced superconductivity with T_c of ∼6 K (∼8 K) above ∼4 GPa (∼1 GPa) for R=Sm (R=Nd). An anomaly corresponding to a magnetic phase transition into spin density wave (SDW) state was observed in the ρ(T) curves in the entire pressure range, indicating that the superconducting and SDW states coexist in the T-P phase diagram. Volume fraction of the superconductivity is found to be very small. This is consistent with the coexistence of the superconducting and SDW phases.

We report the superconductivity of the topological nodal-line semimetal candidate Sn_xNbSe_2-δ with a noncentrosymmetric crystal structure. The superconducting transition temperature T_c of Sn_xNbSe_2-δ drastically varies with the Sn concentration x and the Se deficiency δ, and reaches 12 K, relatively higher than those of known topological superconductors. The upper critical field of this compound shows unusual temperature dependence, inconsistent with the WHH theory for conventional type-II superconductors. In a low-T_c sample, the zero-temperature limit of the upper critical field parallel to the ab plane exceeds the Pauli paramagnetic limit estimated from the simple BCS weak coupling model by a factor of ∼ 2, suggestive of unusual superconductivity stabilized in Sn_xNbSe_2-δ. Together with the robust superconductivity against disorder, these observations indicate that Sn_xNbSe_2-δ is a promising candidate to explore topological superconductivity.

Have you been lying awake wondering what symmetries determine whether a superconductor is spin-singlet, triplet, or both? We show that if one supplies additional degrees of freedom to BCS theory, spin-singlet can coexist with spin-triplet superconductivity. We guide the reader to the most general superconducting state using symmetry arguments. If both singlet and triplet pairing channels act, a magnetic field can convert between spin-singlet and triplet states. Two possible singlet-triplet superconductors candidates are: CeRh₂As₂ and bilayer-NbSe₂.

We discuss feedback effects that stabilize the superconducting states by the induced topological term in the effective Lagrangian. The chiral feedback effect due to the Chern-Simons-like term for quasi-two-dimensional system with time-reversal symmetry breaking (TRSB) was studied in [1, 2]. We consider the extension of the chiral feedback to three-dimensional TRSB system and investigate similar feedback effects for quasi-two-dimensional or three-dimensional time-reversal symmetric systems.

We investigate the low-energy electronic properties and construct the effective model Hamiltonians in the normal state for new materials BaPtSb and BaPtAs with ordered honeycomb structures. The preliminary experimental study suggested that the former compound may be a candidate of the time-reversal symmetry breaking superconductors. The low-energy electronic structures obtained from the first principles calculation mainly consist of Pt 5d and Sb/As 5p/4p orbitals, where there exist the strong hybridizations between both orbitals. We show that the main parts in the low-energy region including the Fermi surface are well described using renormalized 3 bands consisting of dominant Pt 2 bands and Sb/As 1 band. Our result provides a starting point for microscopic investigation in the superconducting states for the materials with the hexagonal structure.

The superconductivity in tungsten bronze A_xWO₃ (A═alkali metal) is studied based on first-principles calculations and orbital fluctuation theory. We discuss the effects of the electron-Jahn-Teller phonon interaction and the on-site Coulomb interaction in the random phase approximation, and obtain a phase diagram on the U — g plane in the low-doped regime at x~0.05, where high-temperature superconductivity has been experimentally observed.

We revisit the superconducting instability mediated by spin fluctuations in generic electron systems on a square lattice. We employ the standard Eliashberg theory, include the electron self-energy, keep a fine momentum resolution, and achieve numerical calculations down to very low temperatures so that the onset temperature of superconductivity (SC) can be determined. We find that spin fluctuations necessarily contain a contribution to suppress SC even though the superconducting instability can eventually occur at lower temperatures. This self-restraint effect stems from the repulsive pairing interaction induced by spin fluctuations, which leads to phase frustration of the pairing gap and consequently the suppression of SC. The self-restraint effect is a special feature of spin fluctuations and does not occur when SC is driven by the attractive pairing interaction from, for example, nematic fluctuations, orbital fluctuations, and electron-phonon coupling.

We develop a minimal non-BCS model for the CuO₂ planes with the on-site Hilbert space reduced to only three effective valence centers CuO₄ with different charge, conventional spin, and orbital symmetry, combined in a charge triplet, to describe the low-energy electron structure and the phase states of HTSC cuprates. Using the S = 1 pseudospin algebra we introduce an effective spin-pseudospin Hamiltonian which takes into account local and nonlocal correlations, one- and two-particle transport, and spin exchange. The T-n phase diagrams of the complete spin-pseudospin model for the CuO₂ planes were reproduced by means of a site-dependent variational approach within effective field approximation typical for spin-magnetic systems. Limiting ourselves to two-sublattice approximation and nn-couplings we arrived at several Néel-like phases in CuO₂ planes for parent and doped systems with a single nonzero local order parameter: antiferromagnetic insulator, charge order, glueless d-wave Bose superfluid phase, and unusual metallic phase. However, the Maxwell's construction shows the global minimum of free energy is realized for phase separated states which are bounded by the third-order phase transition line T*(n), which is believed to be responsible for the onset of the pseudogap phenomenon.

We investigate the pairing symmetry of the ordered honeycomb network superconductor BaPtSb, which has a crystal structure without inversion center. There is a preliminary μSR report which implies the broken time-reversal symmetry in the superconducting state. In this paper, we classify the pairing symmetry and examine the pairing instability. Among the unconventional states with time-reversal symmetry breaking, we find that the state with a gap structure compatible with Fermi surfaces is the spin-triplet chiral p-wave state.

We discuss the chiral superconducting state in a square lattice system with an intrinsic spin-orbit coupling causing the spin Hall effect. We estimate the spontaneous spin polarization (local moment) 〈m_i〉 at the i-th site and its sum M = ∑_i 〈m_i〉 in ribbons. In the zigzag ribbon, we see 〈m_i〉 ≠ 0 near the edge. The energy spectra of the chiral edge states show the spin splitting and then we have non-zero M. Moreover, we find that M is enhanced significantly at a topological phase transition point, where the energy gap is closing. We also have non-zero 〈m_i〉 near the edge of the straight ribbon, but in contrast, there is no spin splitting in the spectra and M vanishes.

The superconductivity in the one-band Hubbard model on a Bethe lattice is investigated on the basis of the dynamical mean-field theory (DMFT) in which the irreducible vertex function has no k-dependence and then only the s-wave superconductivities with the spin-singlet even-frequency and the spin-triplet odd-frequency pairings are possibly realized. We calculate the pair susceptibility by solving the Bethe-Salpeter equation with the use of the linearized DMFT and find that the spin-singlet pair susceptibility is suppressed by the on-site Coulomb interaction U especially for the region near the Mott transition. On the other hand, the spin-triplet pair susceptibility is apparently enhanced by U in the strong correlation regime at very low temperatures where the effective interaction for the triplet pairing is considered to be attractive and then the triplet superconductivity is expected to be realized.

Machine learning (ML) methods have proved to be a very successful tool in physical sciences, especially when applied to experimental data analysis. Artificial intelligence is particularly good at recognizing patterns in high dimensional data, where it usually outperforms humans. Here we applied a simple ML tool called principal component analysis (PCA) to study data from muon spectroscopy. The measured quantity from this experiment is an asymmetry function, which holds the information about the average intrinsic magnetic field of the sample. A change in the asymmetry function might indicate a phase transition; however, these changes can be very subtle, and existing methods of analyzing the data require knowledge about the specific physics of the material. PCA is an unsupervised ML tool, which means that no assumption about the input data is required, yet we found that it still can be successfully applied to asymmetry curves, and the indications of phase transitions can be recovered. The method was applied to a range of magnetic materials with different underlying physics. We discovered that performing PCA on all those materials simultaneously can have a positive effect on the clarity of phase transition indicators and can also improve the detection of the most important variations of asymmetry functions. For this joint PCA we introduce a simple way to track the contributions from different materials for a more meaningful analysis.

A pair of split superconducting transitions in the presence of a symmetry breaking field is a very definitive signature of multi-component superconductivity[1, 2]. We theoretically study the shear modulus anomaly across such pair of split transitions[3]. The talk will be focused on MxBi2Se3, a nematic superconductor candidate, for which no experimental confirmation of the split transition has been made so far. We propose that the shear modulus C₆₆ must vanish at the lower transition: a very clear signature detectable by experiments. The observation of shear modulus anomalies would be a conclusive test for the nematic superconductivity hosted by the material.

We consider an electron model of superconductivity on a three-dimensional lattice where there are on-site attractive Hubbard interaction and long-range repulsive Coulomb interaction. It is claimed that fully gapped s-wave superconductivity within this model, if present, exhibits spontaneous translation symmetry breaking possibly related to a charge order. Our discussions are based on an application of the Lieb-Schultz-Mattis theorem under some physical assumptions. The inconsistency between the proposed supersolid and experiments can impose some constraints on a reasonable choice of a theoretical model.

The complex high-frequency conductance of high-mobility n-GaAs/AlGaAs heterostructures was determined in magnetic fields 12–18 T using the Surface Acoustic Waves technique. Analysis of frequency and temperature dependences of conductance showed that in the investigated magnetic field range and at low temperatures, T<200 mK, the electron system forms a Wigner crystal deformed due to pinning by disorder. We have also defined an effective melting temperature of the Wigner crystal.

We investigate the quantum phase transitions of a phase-glass model in a magnetic field with frustration parameter f = 1/2, describing the effects random negative Josephson-junction couplings in two-dimensional superconductors. The critical behavior is obtained by a scaling analysis of path-integral Monte Carlo simulations at zero temperature, including corrections to finite-size scaling. A single superconducting and chiral-glass to insulator transition occurs above a disorder threshold with divergent nonlinear magnetic susceptibility, unaffected by the additional magnetic-field frustration. The relevance of this transition for nanohole superconducting thin films doped with magnetic impurities is discussed.

We consider a two-dimensional electron gas in the thermodynamic (bulk) limit. It is assumed that the system consists of fully spin-polarized (spinless) electrons with anisotropic mass. We study the variation of the shape of the expected elliptical Fermi surface as a function of the density of the system in presence of such form of internal anisotropy. To this effect, we calculate the energy of the system as well as the optimum ellipticity of the Fermi surface for two possible liquid states. One corresponds to the standard system with circular Fermi surface while the second one represents a liquid anisotropic phase with a tunable elliptical deformation of the Fermi surface that includes the state that minimizes the kinetic energy. The results obtained shed light on several possible scenarios that may arise in such a system. The competition between opposing tendencies of the kinetic energy and potential energy may lead to the stabilization of liquid phases where the optimal elliptical deformation of the Fermi surface is non-obvious and depends on the density as well as an array of other factors related to the specific values of various parameters that characterize the system.

The S = 1/2 Kitaev honeycomb model has attracted significant attention as an exactly solvable example with a quantum spin liquid ground state. In an properly oriented external magnetic field, the system exhibits chiral Majorana edge modes with an associated quantized thermal Hall conductance, and a distinct spin-disordered phase emerges at intermediate field strengths, below the polarized phase. However, since material realizations of Kitaev magnetism invariably display competing exchange interactions, the stability of these exotic phases with respect to additional couplings is a key issue. Here, we report a 24-site exact diagonalization study of the Heisenberg-Kitaev model in a magnetic field applied in the [001] and [111] directions. By mapping the full phase diagram of the model and contrasting the results to recent nonlinear spin-wave calculations, we show that both methods agree well, thus establishing that quantum corrections substantially modify the classical phase diagram. Furthermore, we find that, in a [111] field, the intermediate-field spin-disordered phase is remarkably stable to Heisenberg interactions and may potentially end in a novel quantum tricritical point.

In an antiferromagnetic zigzag chain, competition between the nearest and next-nearest neighbor interactions could give rise to magnetic frustration. Magnetic semiconductors RAgSe₂ (R = Ho, Er, Tm, and Yb) crystallize in the ErAgSe₂-type orthorhombic structure, where the R ions form a zigzag chain along the orthorhombic a-axis. The magnetic susceptibility data for all the samples follow the Curie-Weiss law between 40 and 300 K. The values of the effective magnetic moment μ_βα are close to those expected for the free R³+ ions. Negative values of the paramagnetic Curie temperature θ_ρ indicate antiferromagnetic interactions. For R = Ho and Tm, the specific heat C(T) data exhibit no anomaly down to 0.4 K, which is ascribed to the nonmagnetic singlet ground states under the crystalline electric fields. On the other hand, for R = Er, C(T) shows peaks at T₁ = 1.3 K and T₂ = 0.9 K, indicating successive antiferromagnetic transitions. For R = Yb, C(T) shows a lambda-type anomaly at T_m = 1.8 K. The magnetic entropy at T_m is only 30% of Rln2 expected for the ground state doublet, suggesting magnetic fluctuations above T_m.

Ternary rubidium-iron sulfide, RbFeS₂, belongs to a family of quasi-one-dimensional compounds with the general chemical composition AFeCh₂ (where A – K, Rb, Cs, Tl; Ch – S, Se). Understanding the magnetic properties of these compounds is a challenge. The controversy concerning the spin-state of the iron ion needs to be resolved to build the proper model of magnetism. Single crystals of RbFeS₂ were grown and characterized by powder x-ray diffraction. QD MPMS-5 SQUID magnetometry was used to measure the magnetic susceptibility, and specific heat was measured utilizing QD PPMS-9 setup. Above the transition to three-dimensional antiferromagnetic order at the Néel temperature of T_N = 188 K, the susceptibility exhibits unusual quasi-linear increase up to the highest measured temperature of 500 K. The specific heat was measured in the temperature range 1.8 – 300 K. Ab initio phonon dispersion and density-of-states calculations were performed by means of density functional theory (DFT), and the calculated lattice specific heat was subtracted from the measured one giving the magnetic contribution to the specific heat. Our results suggest that the features of the magnetic specific heat are general for the whole family of the covalent chain ternary iron chalcogenides of the AFeCh₂ structure and indicate an intermediate S = 3/2 spin state of the iron ion.

We have performed ⁶³Cu-nuclear quadrupole resonance (NQR) measurements using a lump sample of the Yb zigzag-chain compound YbCuS₂ with a small surface area to investigate the sample dependence of low-temperature magnetic properties in YbCuS₂ by comparing with the previous study with different powdered sample. The line width of NQR signals in the present lump sample is larger than that in the previous powdered sample. In addition, the transition temperature T_N ∼ 0.92 K in the present lump sample is lower than that in the previous powdered sample (∼ 0.95 K). These results suggest that the quality of the present lump sample is worse than that of the previous powdered sample. However, the T-linear behavior of the nuclear spin-lattice relaxation rate 1/T₁ was observed below 0.5 K and the value of 1/T₁T in both samples is almost the same even though the sample quality and sample geometry are different. This suggests that T-linear behavior in 1/T₁ arises from the impurity-robust bulk gapless excitation inherent in YbCuS₂ rather than from sample issues such as the sample quality or geometry.

We investigate the anisotropic S = 1/2 Kitaev model on the honeycomb lattice with the ordered-flux structure. By diagonalizing the Majorana Hamiltonian for the flux configuration, we find two distinct gapped quantum spin liquids. One of them is the gapped state realized in the large anisotropic case, where low energy properties are described by the toric code. On the other hand, when the system has small anisotropy, the other gapped quantum spin liquid is stabilized by the ordered-flux configuration. Since these two gapped quantum spin liquids are separated by the gapless region, these are not adiabatically connected to each other.

We have recently proposed a new concept of cluster-based Haldane states supported by an inherent chirality in a triangular spin tube with equivalent inter-cluster interactions. In this state, there appear spin-1/2 degrees of freedom consisting of a real spin and a scalar chirality as edge states. With applying a magnetic field, we can observe approximately a half of magnetization of S = 1/2 spin, i.e., a quarter spin magnetization, due to symmetrization of the real spin and the chirality. Here, we consider effects of discord between two types of inter-cluster interactions, inducing anisotropic biquadratic interactions of effective S = 1 spins. The discord brings the edge magnetization nearer to an exact value of quarter spin magnetization, whereas localization of the edge states becomes worse. These effects are also confirmed in a corresponding spin-1 model.

The magnetization process of the S = 1 antiferromagnetic chain with the single-ion anisotropy D and the biquadratic interaction is investigated using the numerical diagonalization. Both interactions stabilize the 2-magnon Tomonaga-Luttinger liquid (TLL) phase in the magnetization process. Based on several excitation gaps calculated by the numerical diagonalization, some phase diagrams of the magnetization process are presented. These phase diagrams reveal that the spin nematic dominant TLL phase appears at higher magnetizations for sufficiently large negative D.

Extensively reported experimental observations indicate that on varying a control parameter, such as pressure p, within the phase diagram of most quantum critical heavy fermion HF superconductors, one identifies a cascade of distinct electronic states which may be magnetic, of Kondo-type, non-conventional superconducting, Fermi Liquid, FL, or non-FL character. Of particular interest is the part of the phase diagram wherein superconductivity emerges from a strongly renormalized FL state. This region resembles the overdoped region of the T-doping phase diagram of cuprate superconductors. Remarkably, within this highly nontrivial region, one identifies a universal correlation among T_c and $A:In\frac{{{T_c}}}{\theta } \propto {A^{ - \frac{1}{2}}}$ (θ is a characteristic energy scale and A is the coefficient of T² resistivity term). Commonly, these features are considered to be driven by a Spin-Fluctuation-mediated electron-electron scattering channel. On adopting such a channel and applying standard theories of Migdal-Eliashberg (superconductivity) and Boltzmann (transport), we derive analytic expressions that satisfactorily reproduce the aforementioned empirical correlations.

Comprehensive analyses of the ¹¹⁵In-NQR spectra employing a magnetic dipolar model and a transferred hyperfine model are performed to determine the magnetic structures of Ce₃PtIn₁₁. Based on this analysis, we confirmed that the magnetic moment at the Ce(1) site is very small (∼ 4% of that at the Ce(2) site) but finite. Further, for T_N2 < T < T_N1 and T < T_N2, the magnetic moments at the Ce(1) and Ce(2) sites are parallel to the c-axis, and the in-plane propagation vectors in the two Ce atoms sublattices are (q_a, q_b) = (1/2, 1/2). In the temperature interval T_N2 <T < T_N1, for example, both of them have a form of q = (1/2, 1/2, 0). For T < T_N2, the magnetic structure in the Ce(2) sublattice is defined by the propagation vector q = (1/2, 1/2, 1/2 or 0), whereas the Ce(1) sublattice forms a six-fold period structure given by q = (1/2, 1/2, 1/6).

CePt₆Al₃ is a rare example of the Ce-based honeycomb lattice compound. Substitution of the isovalent Pt for Pd transforms the ground state from a paramagnetic heavy-fermion state to an antiferromagnetic (AFM) ordered state. To gain insight into the role of magnetic frustration in the honeycomb Kondo lattice, we have measured the magnetization M(B) and electrical resistivity ρ(B) of Ce(Pt_1-xPd_x)₆Al₃ (x ≤ 0.3) in pulsed magnetic fields up to 60 T. For the single crystal with x = 0, M(B) for B along the easy c axis exhibits a metamagnetic increase and ρ(B || c) bends at B_m = 28 T. Taking the temperature at a shoulder in the magnetic susceptibility χ^(ल) for B || c as T_χm = 17 K, the ratio _μBB_m/K_BT_>χm is estimated to be 1.1. This value agrees with those reported for Ce-based paramagnetic heavy-fermion compounds with similar magnitudes of B_m. With increasing x from 0 to 0.3 in polycrystalline samples, the magnitude of M(B = 60 T) at 1.4 K increases from 0.75 to 2.0 _μβ/Ce, indicating the recovery of localized 4f moments by the Pd substitution for Pt. Using the data of M(B) and ρ(B) for x = 0.1, 0.2, 0.3, we constructed B-T phase diagrams, which show a trend from a small moment AFM ordered state for x = 0.1 to a large moment AFM ordered state for x = 0.3.

The thermal expansion of a diluted Ce system La_1-xCe_xCu₆ for (0.6 ≤ x ≤ 1) has been measured between 10 and 150 K to reveal the change from the coherent heavy Fermion state (0.9 ≤ x ≤ 1) to the incoherent Kondo state (0 < x ≤ 0.73). The large Ce concentration x dependence of the linear thermal expansion coefficient along b-axis α_b(T) suggests that the coupling between the 4f¹ electron and the lattice strain is the largest along the b-axis in the three crystallographic axes. The maximum of the magnetic contribution to the volume thermal expansion coefficient β_m(T) at T = 50 K is retained in the x range of 0.6 ≤ x ≤ 1, suggesting the crystalline electric field (CEF) level for x = 1 doesn't change by the substitution. Furthermore, the upturn in β_m(T) below 25 K, which should be a precursor of the maximum at T = 2.5 K reported for x = 1, is retained when we decrease x from 1 to 0.6. Because the ground state for x = 0.6 is the incoherent Kondo state, the robustness of the maximum at T = 50 K and upturn in the current x value implies that β_m(T) in 10 ≤ T ≤ 150 K is attributed to the CEF and Kondo effects rather than the formation of the heavy Fermion state.

Magnetic and transport properties of a new cubic compound CeMgZn₂ have been examined by measuring the magnetic susceptibility, the magnetization, the electrical resistivity, and the specific heat. CeMgZn₂ is a Kondo-lattice compound with trivalent Ce ions. The magnetic susceptibility measured at 0.1 T exhibits a shoulder and a cusp at T_N1 = 5.4 K and T_N2 = 3.1 K, respectively. T_N1 and T_N2 correspond to the antiferromagnetic-transition temperatures since these temperatures decrease with increasing magnetic field. The large value of the paramagnetic Curie temperature divided by T_N1 (13.5) implies that T_N1 is suppressed by geometrical frustration on a face-centered cubic Ce sublattice. The geometrical frustration may also be responsible for the appearance of many magnetic phases in magnetic fields.

We have synthesized polycrystalline samples of CePtAl₂ by arc melting method and examined their magnetic, transport and thermal properties by measuring the magnetization, the electrical resistivity, and the specific heat down to 0.4 K. As a result of these measurements, we found that CePtAl₂ is a ferromagnetic Ce-based compound with the Curie-temperature Tc = 2.7 K.

We have prepared polycrystalline samples of RE₂Au₃Sn₆ (RE = Ce, La) and investigated their magnetic, transport and thermal properties. We found that Ce₂Au₃Sn₆ shows antiferromagnetic transition at T_N = 2.54 K, while La₂Au₃Sn₆ shows no phase transition above 0.4 K. The electronic specific heat coefficient of Ce₂Au₃Sn₆ is γ = 350 mJ Ce-mol K², which indicates that Ce₂Au₃Sn₆ is a heavy fermion compound. The magnetic entropy of Ce₂Au₃Sn₆ at T_N is estimated to be 70% of Rln2, which can be attributed to the shielding of the magnetic moment by the Kondo effect.

Magnetic, transport, and thermal properties of new orthorhombic compounds Ce₄Pt₉Al₁₃ and Ce₄Pt₉Al₁₃ have been investigated by the magnetization, the electrical resistivity, and the specific-heat measurements. Ce₄Pt₉Al₁₃ is a Kondo-lattice compound and shows a ferromagnetic or ferrimagnetic transition at T_C = 0.88 K. Pr₄Pt₉Al₁₃ is an antiferromagnetic compound with the transition temperature at T_N = 2.6 K.

We have synthesized polycrystalline samples of a new orthorhombic compound Ce₂lr₃Sb₄ and investigated their physical properties by measuring the magnetization, the electrical resistivity, and the specific heat down to 0.4 K. From the results of electrical resistivity measurements, it was found that Ce₂Ir₃Sb₄ is a Kondo lattice compound. We found that Ce₂Ir₃Sb₄ does not show any phase transition down to 0.4 K. The specific heat peak at 1.3 K is not due to a phase transition but due to the Schottky specific heat caused by the crystalline electric field splitting of the 4f level of Ce ions.

We performed electrical resistivity measurements of Ce₃TiSb₅ under pressure. From the pressure dependences of antiferromagnetic ordering temperature T_N and lower anomalous temperature T*, temperature–pressure phase diagram of Ce₃TiSb₅ up to 2.3 GPa has been constructed. T* rapidly decreases with increasing pressure and disappears around 1 GPa. T_N increases with increasing pressure, however a hump structure of electrical resistivity below T_N becomes small. Hence, some change for the magnetic ordered state is expected to occur in higher pressure region.

In this work, we investigated the role of different parameters in the synthesis of intermetallic nanowires of CeIn₃ by the metallic-flux nanonucleation (MFNN) method such as template pore diameter, crystallization temperature, heat treatment temperature, and synthesis time. Depending on the growing parameters, we obtained CeIn₃ nanowires (d ∼ 350 nm) or CeAlO₃ nanotubes. For the nanowires, we observed a suppression of the CeIn₃ antiferromagnetic transition from the bulk T_N ∼ 10 K to the nanowire system T_N ∼ 3 K, which may be associated with the dimensionality affecting the interplay between magnetic exchange interactions, crystalline electrical field, and Kondo effects. We assume that the CeAlO₃ nanotubes may result from a reaction with the alumina template and consequent rare-earth oxidation. Our work shows that even it is a great challenge to find the correct growth path of a particular intermetallic compound, the MFNN method can be a promising route to obtain rare-earth based nanowires.

We report magnetoelastic studies in the CeCo_1−xFe_xSi alloys. Iron doping has a profound effect on the low temperature linear magnetostriction. At T = 2 K, the strength of the magnetostriction peaks at x = 0.23 where it reaches a value as large as $\[\frac{{\Delta L}}{L} = 3 \times {10^{ - 3}}\]$ in an applied magnetic field B = 16 T. This Fe concentration corresponds to the critical one x_c above which long-range antiferromagnetic order is no longer observed. The progressive increment of the hibridization between the Ce 4f orbital and the conduction band, as the magnetic order vanishes, gives rise to a sizeable valence susceptibility that can be finely tuned by the magnetic field explaining the large magnetostrictive effect around x_c. At higher x, the magnetostriction decreases, in agreement with a weaker valence susceptibility resulting from a stronger hibridization.

We examined the effect of 3p- and 5d-electron doping on the Kondo semiconductor CeFe₂Al₁₀ by means of the electrical resistivity (ρ), magnetic susceptibility (χ), and specific heat (C) measurements. The results show that in the 3p-electron-doped system CeFe₂Al_10−ySi_y, the semiconducting behavior is suppressed for y = 0.05, and the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The Si substitution leads to a large decrease in the paramagnetic Weiss temperature θ_P indicating a reduction in c-f hybridization strength, however the Si does not induce magnetic order up to y = 0.3 down to 2K. The systematic changes in ρ(T), χ(T), and C(T) are similar to those for 5d-electron doped system CeFe_2−xIr_xAl₁₀, although, Ir substitution induces a bulk antiferromagnetic transition below 3.1 K in CeFe_1.7Ir_0.3Al₁₀. These changes can be explained by the collapse of the hybridization gap due to the suppression of the c-f hybridization effect. Our results further confirm that the collapse of the spin/charge gap by an excess electron doping is one of the universal features of the Kondo semiconductors CeT₂Al₁₀ (T = Fe, Ru, and Os).

We study the electronic properties of a Ce-based Kondo material, CeCuAs₂ employing high-resolution hard x-ray photoemission spectroscopy. The measurements were done with different photon energies to probe the surface-bulk differences of the electronic structure. Experimental results show significant difference in the hybridization physics for the surface and bulk electronic structures indicating different Ce valency at the surface compared to the bulk. Surface termination appears to play an important role in the correlation physics of this system. In addition, the experimental spectra show loss features due to plasmon excitations. These results bring out complexity of this novel Kondo lattice system that does not show magnetic order down to the lowest temperature studied and have significantly different surface-bulk properties.

We investigate the electronic structure of a cobalt atom in a copper host using the density functional theory and the exact diagonalization of an Anderson impurity model. The spectral functions and spin moments at the impurity are calculated and are found to be close the ones calculated by DFT+QMC [1].

The resistive switching observed under electric pulses in Mott materials has a high potential for micro and nanoelectronics. Here we report on the study of the resistive switching observed at the surface of single crystals of the canonical Mott semiconductor GaMo₄S₈. The study is made using a multiprobe setup with 4 nanopositionable tips under the supervision of a high resolution scanning electron microscop. We find a resistivity of 38 Ω.cm by four-point probe measurements, in agreement with the literature. The volatile insulator to metal transition is studied with a two probes configuration for interelectrode distances varying between 4 and 200 microns. Finite element simulations are performed to determine the spatial distribution of the electric field prior to the transition. Our results are in agreement with i) an intrinsic voltage threshold of 60 mV independent of the interelectrode distance ii) a maximum electric field close to the electrodes and iii) a threshold electric field of 0.2 kV/cm.

We studied the structural, static, and dynamic properties of Ca₃Co_2–xBi_xO₆ (x = 0 and 0.2) by means of powder X-ray diffraction and magnetization measurements. We reveal the rejuvenation phenomena in magnetic relaxation under cyclic temperature change and quenching below T_c2. The reproduced step in the memory curve confirms the striking feature of rejuvenation effect in these samples. The observed memory and rejuvenation effects are discussed in the framework of hierarchical model of glassy phase.

A growing body of evidence reveals that charge density wave (CDW) transport is a high-temperature cooperative quantum phenomenon. According to the time-correlated soliton tunneling (ST) model, quantum solitons, or electron-phonon correlates within the CDW condensate, act much like electrons tunneling through a Coulomb-blockade tunnel junction. Pair creation of charged fluidic soliton droplets is prevented by their electrostatic energy below a Coulomb-blockade threshold electric field. Above threshold, the quantum fluid flows in a periodic fashion, via a hybrid between Zener-like and coherent Josephson-like tunneling. We summarize the time-correlated ST model and compare model simulations with experiment. The ST model shows excellent agreement with coherent voltage oscillations, and with CDW current-voltage characteristics. Finally, we discuss implications for physics and potential applications.

We investigate momentum-dependent transient spin dynamics after photoirradiation in a two-dimensional Mott insulator described by a half-filled Hubbard model on a square lattice by using a numerically exact-diagonalization technique. We find a temporal oscillation in the static spin structure factor of a $\sqrt {18} \times \sqrt {18}$ periodic lattice. The oscillation exhibits an antiphase behavior between, for example, two orthogonal momentum directions parallel and perpendicular to the electric field of a pump pulse. The origin of the antiphase oscillation is attributed to a photoexcited wave function that has overlap with eigenstates producing the B_1g bimagnon Raman intensity. Observing such antiphase oscillations will be a big challenge for time-resolved resonant elastic x-ray scattering experiments.

We study the effects of the photo irradiation on the band insulating state in the two-band Hubbard model on the Penrose tiling. Examining the time- and site-dependent physical quantities, we find that the excitionic state is dynamically induced with site-dependent order parameters. It is also clarified that, in the excitonic state induced by the photo irradiation, local oscillatory behavior appears in the electron number as well as in the order parameter, which should be characteristic of the quasiperiodic lattice.

Using the Lindblad equation approach, we study the nonequilibrium stationary state of a benzene ring connected to two reservoirs in the large bias regime, a prototype of a generic molecular electronic device. We show the emergence of an optimal working point (corresponding to a change in the monotonicity of the stationary current, as a function of the applied bias) and its robustness against chemical potential and bond disorder.

We performed inelastic neutron scattering experiments on PrMgNi₄ with the cubic MgSnCu₄-type structure. The magnetic excitations were observed at 1.1, 2.5, 5.9, 10.7, and 11.7 meV. Since the energy of the excitations is constant for |Q| < 5 Å⁻¹, they are ascribed to the crystalline electric field (CEF) excitations of the Pr³⁺ ions. We adopted CEF parameters of W = −3.3 K and x = 0.8 for the cubic T_d point group to reproduce the strong excitations at 1.1, 10.7, and 11.7 meV. The calculated CEF level scheme reveals the Γ₃ doublet ground state with the quadrupolar degrees of freedom and the excited states of Γ₄ triplet (1.4 meV), Γ₁ singlet (3.4 meV), and Γ₅ triplet (13.5 meV). This scheme, however, does not explain the observed two excitations at 2.5 and 5.9 meV. These additional excitations may arise from splitting of the doublet by symmetry lowering due to excess Mg atoms occupying the Pr sites. This splitting is probably responsible for the absence of the long-range quadrupole order in PrMgNi₄.

Powder neutron diffraction measurements were carried out to investigate the magnetic structure of the antiferromagnet NdRh₂Zn₂₀. The magnetic reflections observed for T ≤ 1.0 K are indexed by the propagation vector of k = (1/2, 1/2, 1/2). From the analysis of the intensity of magnetic reflections, a magnetic structure described by the Γ₆ representation is proposed. The magnetic moments are parallel to the $\[[11\bar 2]\]$ or $\[[\bar 110]\]$ direction and stacked with a sequence of up-up-down-down along the [111] direction.

We present Raman-scattering results for three materials, CeB₆, TbInO₃, and YbRu₂Ge₂, to illustrate the essential aspects of crystal-field (CF) excitations and quadrupolar fluctuations of 4f-electron systems. For CF excitations, we illustrate how the 4f orbits are split by spin-orbit coupling and CF potential by presenting spectra for inter- and intra-multiplet excitations over a large energy range. We discuss identification of the CF ground state and establishment of low-energy CF level scheme from the symmetry and energy of measured CF excitations. In addition, we demonstrate that the CF linewidth is a sensitive probe of electron correlation by virtue of self-energy effect. For quadrupolar fluctuations, we discuss both ferroquadrupolar (FQ) and antiferroquadrupolar (AFQ) cases. Long-wavelength quadrupolar fluctuations of the same symmetry as the FQ order parameter persists well above the transition temperature, from which the strength of electronic intersite quadrupolar interaction can be evaluated. The tendency towards AFQ ordering induces ferromagnetic correlation between neighboring 4f-ion sites, leading to long-wavelength magnetic fluctuations.

CeNi₅ as a mother compound is well known as a Stoner enhanced paramagnet characterized by the spin fluctuation contribution on its transport properties. Previous work on CeNi₄Cr compound showed typical features of mixed valence systems with indication of tendency to heavy fermion behavior [1]. The theoretically predicted phase transition into antiferromagnetic order wasn't observed down to 2 K. In this work we present the effect of spin fluctuations of the CeNi₄Cr compound focused on its thermodynamic properties

We present the results of inelastic neutron scattering (INS) measurements on Kondo lattice heavy fermion CeCuGa₃. The low-temperature magnetic susceptibility exhibits an anomaly near 2.6 K associated with an antiferromagnetic transition which is further confirmed by the heat capacity measurement. The analysis of magnetic heat capacity C_mag (T) based on the crystal electric field (CEF) model reveals an overall CEF splitting of ∼ 21 meV. The INS data reveal two strong magnetic excitations near 4.5 and 6.9 meV, which, however failed to reproduce the observed C_mag (T). We therefore analyze the INS data by a model based on magneto-elastic (i.e. CEF-phonon) coupling which suggests that the excitations observed near 4.5 and 6.9 meV originate from the CEF-phonon coupling as observed in CeCuAl₃ and CeAuAl₃.

In this study, we investigate the electronic structure of FeSe in the normal and nematic states based on the DFT+U method in combination with the multipole analyses, and discuss their microscopic properties and origin. In the normal state, the topological change of the Fermi surface occurs before the nematic transition with increasing the on-site Coulomb interaction U. The resulting nematic ground state is a multipolar state having both hexadecapoles in the E-representation and multipoles in the B₂-representation on each Fe site, where the appearance of the E-type multipoles induces non-trivial spontaneous orbital hybridizations between d_xy, d_x²-y² and d_xz/d_yz orbitals. Such the spontaneous orbital mixings due to E-type multipoles is inherent in the FeSe and related systems, and is expected to play an important role in the formation of the nematic states in other iron-based superconductors.

We point out the scientific importance of the increasing evidence for the existence of the discrete low-energy meV-energy states in compounds containing atoms with incomplete 4f, 5f, 3d shells and recently in iridates (5d shell). We point out that the realized charge state of the 3d/4f/5f/4d/5d atoms/ions in oxides is very close to the formal one obtained within the ionic model. In Ba₂IrO₄ the charge states are very close to Ba²⁺, Ir⁴⁺ and O²⁻. In CeRh₂Si₂, which is intermetallic and considered as a Kondo-lattice antiferromagnet, by detailed analysis of temperature dependence of the specific heat we have proved the realization of the trivalent charge state of practically all cerium ions. In the magnetic state, below T_N of 36 K, the Kramers doublet becomes split and there appears a spin gap growing to 6 meV at T = 0 K.

We investigate the effect of many-body interactions on the spin-orbit coupling of anisotropic metals. We use the Underscreened Anderson Lattice Model that was proposed to describe actinide compounds. The Coulomb interactions induce off-diagonal correlations that enhance the components of the spin-orbit coupling. Modest values of the Coulomb interaction U can significantly enhance the spin-orbit coupling and effect the electronic spectrum. The enhancements are most pronounced for systems that are on the verge of magnetic instabilities. The enhancement is anisotropic in crystals with non-cubic symmetries and can lead to giant magnetic anisotropies in paramagnetic states.

We analyze the finite-temperature scaling of the Lorenz ratio at the topological Kondo fixed point realized at a junction of three interacting quantum wires connected to a floating superconducting island. Using the Tomonaga-Luttinger liquid approach to the quantum wires, we derive the full functional dependence of the finite-temperature correction on the Luttinger parameter g.

Single crystals of WTe₂ have been prepared using the flux method. Analysis of the x-ray diffraction pattern shows the pure phase of the sample. Temperature dependent resistivity indicates the metallic nature of the sample. The residual resistance ratio of the sample has been found very high providing further evidence of the good quality of the crystals. Extremely high magnetoresistance has been observed in the sample. Quantum oscillations have been seen at high field. Fast Fourier transformation of the quantum oscillations shows nearly the same size of the electron and hole pocket in the sample.

BiPd is a noncentrosymmetric superconductor with Dirac-like surface states on both (010) and $\[(0\bar 10)\]$ faces. The Dirac cone on (010) surface is intense and appears at 0.66 eV binding energy. These states have drawn much attention due to contradictory reports on dimensionality and the momentum of these Dirac fermions. We have studied the properties of these Dirac fermions using varied photon energies and different experimental conditions. The behavior of the Dirac cone is found to be two-dimensional. In addition, we found few more surface states appearing at higher binding energies compared to the Dirac cone.

An isotropic tight-binding model with the nearest-neighbour hopping on a pyrochlore lattice gives a rich variety of physical properties due to the emergence of the flat-band. Moreover, by introducing spin-orbit coupling into this model, the topological properties of the system changes significantly. This model is well applicable to some pyrochlore oxides called s1/s2 pyrochlores. In this paper we apply this model to an s2 pyrochlore oxide Pb₂Ta₂O₇ and found a characteristic quadratic touching of the quasi-flat band and dispersive band. Furthermore, when a ferromagnetic order appears due to this quasi-flat band, a pair of Weyl points appears in that direction.

Spin-momentum locking is becoming a cornerstone for the understanding and applications of novel condensed matter systems. Here we assume that it holds locally in position space and from it predict the existence of a local magnetic field. Although residual, this local magnetic field is important because it brings the topological stability that transforms particles into quasi-particles. The present approach shows that the Rashba term is already contained in the Schrödinger kinetic energy and a Dirac linear spectrum can be obtained without invoking a Dirac equation for the particles.

Noncollinear antiferromagnets Mn₃X (X = Sn, Ge) are characterized by a large anomalous Hall effect originating from a large Berry curvature despite a vanishingly small magnetization. From recent first-principle theories, the large Berry curvature is predicted to be induced by a existence of Weyl nodes broken time-reversal symmetry. The large anomalous Nernst effect is also contributed by the magnetic Weyl state around the Fermi level E_F, and likely shares its origin with the anomalous Hall effect. The thermoelectric transport S(T) and thermomagnetic transport S_ji(T) are thus investigated in single crystals of Mn₃X. Here, Mn₃X exhibits a large anomalous Nernst effect; in particular, the signal magnitude of Mn₃Ge exceeds 1μV/K, which is 1.5 times that of Mn₃Sn. The Weyl properties are discussed by analyzing the thermal conductivity, specific heat, and Seebeck and Nernst effects. We also evaluate the zero-field Nernst-driven thermoelectric figure of merit for device applications in the antiferromagnets Mn₃X.

The study reveals the comparison of Nd_0.9Pr_0.1CrO₃ and Nd_0.9Eu_0.1CrO₃ samples where the A-site is doped by Pr³⁺ having the larger ionic radius (1.126 A°) corresponding to less chemical pressure and Eu³⁺ (1.066 A°) having the smaller ionic radius corresponding to enhanced chemical pressure exerted on the NdCrO₃, with the help of X-ray diffraction, Raman spetroscopy, UV-visible spectroscopy, and dc magnetization measurements. The different spin configuration Pr³⁺ (J = 4) and Eu³⁺ (J = 0) altering the strong coupling between Nd³⁺ (J = 9/2) and Cr³⁺ (S = 3/2) spins result in the variation of the optical band gap, fermi energy and exchange bias.

Polycrystalline FeCr₂O₄ samples have been synthesized by the solid-state reaction method and studied with X-ray diffraction and Mössbauer spectroscopy. Rietveld refinement of X-ray diffraction pattern has been performed; obtained unit cell parameters are in a good agreement with ones in the literature. Mössbauer spectra were measured at room temperature and reveal by two components originating from the A and B sites of the spinel structure occupied by iron ions.

We theoretically study the electrical conductivity in a one-dimensional helimagnet whose spin texture changes from helimagnetic to conical magnetic, and to forced ferromagnetic state while increasing the magnetic field along the helical axis. We find that the conductivity in the helimagnetic state at zero field depends on the electron filling and the coefficient of the spin-charge coupling. We also find that the conductivity in the conical magnetic state changes nonlinearly to the applied field, and the magnetoresistance becomes negative and positive depending on the model parameters.

We theoretically study skyrmion lattices realized in a Kondo lattice model on a triangular lattice, focusing on the phase, ellipticity, and angle of the constituent multiple-Q waves. Analyzing the numerical data obtained in the previous study [Ozawa R, Hayami S and Motome Y 2017 Phys. Rev. Lett. 118 147205], we extract these parameters for the two types of skyrmion lattices with the skyrmion number of 1 and 2. We show that the topological transition between the two skyrmion lattices driven by an external magnetic field is accompanied by significant modulations of all three parameters.

Any metal-insulator transition in a crystalline matter must be the transition from a situation in which the electronic bands overlap to that when they do not [1]. On the basis of the phenomenological theory [2], various singularities are considered in the magnetic field for the surface tension at the metal-insulator contact. The surface tension displays also the quantum magnetic oscillations at low temperatures [3]. The consideration is applied to the Mott insulator in the magnetic field.

We investigate the magnetic field effect on the Kitaev model with the Γ-type interaction, which plays an essential role in understanding the magnetic properties of real materials. We examine the mean-field phase diagram and thermal Hall conductivity using the linear spin-wave theory. We find that the Γ interaction substantially changes the field-angle dependence of the thermal Hall conductivity and suppresses its magnitude. The suppression is caused by the enhancement of the low-energy magnon gap while increasing the Γ interaction.

Orthorhombic YAlGe-type TbAlGe is expected to have an interesting magnetic anisotropy due to zigzag chains of the Tb ions. We have grown the single crystal for the first time and measured the AC magnetic susceptibility and specific heat from 1.3 K to 60 K, and the vector magnetization for the b-plane up to 7 T at 4 K. The specific heat and AC magnetic susceptibility indicate that there are two antiferromagnetic transitions at T_N1 = 38 K and T_N2 = 7.6 K, where the transition at T_N2 is first-order like. The magnetization curve at 4 K for the a-axis shows a large hysteresis, and metamagnetic transition appears at H₁ = 1.6 T in the field increasing process, and another metamagnetic transition at H₂ = 3.5 T in addition to H₁ in the decreasing field process. The magnetization curves of the b- and c-axis are linear up to 7 T. The measurement of vector magnetization at 4 K reflects the hysteresis of the magnetization curve, and there is a large hysteresis. From this vector magnetization measurement, we have made the angular magnetic field phase diagram at 4 K for the b-plane. In this phase diagram, there are phase lines that cannot be obtained by ordinary magnetization measurement.

We have developed an adiabatic specific heat measurementt using a 4 K GM refrigerator system that can measure down to 1.3 K with exactly the same accuracy as liquid helium environmen. The cryogenic environment can be obtained by liquefying about 20 L of helium gas at room temperature into a 1 K pot by a cascade method and evacuating it with a rotary pump. The 1 K pot temperature reaches 1.2 K. The specific heat measurement probe is mounted on the 1 K pot and is covered with three radiation shields, and the helium liquefied in the 1 K pot is maintained for about 70 minutes after the refrigerator is stopped, and the 1 K pot temperature maintains below 1.5 K. In this state, the specific heat from 1.3 K to 10 K can be measured. By tightly fixing the adenda to the support (base), temperature fluctuations due to mechanical vibration of the refrigerator can be greatly suppressed, and above 2.5 K, specific heat measurement with almost the same accuracy as when the refrigerator is stopped can be performed. By combining these two types of measurements, we can measure the specific heat with exactly the same accuracy as in a liquid helium environment.