We investigate the physical properties of the Shastry-Sutherland lattice material ${\mathrm{BaNd}}_2{\mathrm{ZnO}}_5$. Neutron diffraction, magnetic susceptibility, and specific heat measurements reveal antiferromagnetic order below 1.65 K. The magnetic order is found to be a $2\text{−}\mathit{Q}$ magnetic structure with the magnetic moments lying in the Shastry-Sutherland lattice planes comprising the tetragonal crystal structure of ${\mathrm{BaNd}}_2{\mathrm{ZnO}}_5$. The ordered moment for this structure is 1.9(1) ${\mu }_B$ per Nd ion. Inelastic neutron scattering measurements reveal that the crystal field ground state doublet is well separated from the first excited state at 8 meV. The crystal field Hamiltonian is determined through simultaneous refinement of models with both the LS coupling and intermediate coupling approximations to the inelastic neutron scattering and magnetic susceptibility data. The ground state doublet indicates that the magnetic moments lie primarily in the basal plane with magnitude consistent with the size of the determined ordered moment.

The emergence of nontrivial quantum states from competing interactions is a central issue in quantum magnetism. In particular, for the realization of the quantum spin-liquid state, extensive studies have been conducted on frustrated systems, such as kagome antiferromagnets and Kitaev magnets. Novel quantum states in magnetic fields have remained elusive despite the prediction of rich physics. This can be attributed to material scarcity and the difficulty of precise measurements under ultra-high magnetic fields. Here, in this study, we develop the Kapellasite-type compound InCu₃(OH)₆Cl₃, whose exchange interactions are in appropriate energy scale to comprehensively elucidate the magnetic properties of the frustrated S = 1/2 kagome antiferromagnet. The one-third magnetization plateau was clearly observed. Moreover, the large temperature-linear term in the heat capacity was observed in the magnetic fields, indicating the excitation of gapless quasiparticles in the vicinity of the plateau. These results shed light on the critical behaviors between quantum spin-liquid and -solid in kagome antiferromagnets under high magnetic fields.

We have performed ${}^{13}\mathrm{C}$ NMR measurements on $\lambda -{(\mathrm{BEDT}-\mathrm{STF})}_2{\mathrm{FeCl}}_4$ to reveal the mechanism of unconventional paramagneticlike behavior observed in $\lambda$-type molecular $\pi -d$ systems. ${}^{13}\mathrm{C}$ NMR spectra and nuclear spin-lattice relaxation rate $1/T_1$ revealed that the $\pi$ and $3d$ electron systems undergo an antiferromagnetic transition simultaneously at 16 K with the assistance of the $\pi -d$ interaction. We found that the sublattice magnetizations of the $\pi$ and $3d$ spins show different temperature dependence below $T_{\mathrm{N}}$, which is derived from the magnetic coupling between the two sublattice systems with different magnetic natures. We discuss the relationship between the two different magnetization processes and the unconventional magnetic behavior in $\lambda$-type molecular $\pi -d$ system.

We have investigated the magnetic properties of lambda-(BEDT-STF)(2) FeCl4 by Mossbauer measurement to reveal the origin of the paramagnetic-like behavior of the 3d spin system observed in lambda-(BEDT-STF)(2) FeCl(4 )using the donor substitution effect. We found that the temperature dependence of the hyperfine fields shows multistep development below T-N of 16K. From comparison of the Mossbauer results and a theoretical model, we demonstrated that the multistep development is caused by coupling between the 3d spins and the pi spins with strong spin correlation. We propose that the multistep development of the hyperfine fields is an intrinsic behavior induced by the pi-d interaction.

We performed heat capacity measurements on the molecular π–d system λ-(BEDT-STF)2FeCl4 to discuss the unconventional paramagnetic-like behavior. We observed a Schottky-type anomaly below TN of 16 K...

Thermodynamic picture induced by π-d interaction in a molecular magnetic superconductor κ-(BETS)₂FeX₄ (X = Cl, Br), where BETS is bis(ethylenedithio)tetraselenafulvalene, studied by single crystal calorimetry is reviewed. Although the S = 5/2 spins of Fe³⁺ in the anion layers form a three-dimensional long-range ordering with nearly full entropy of Rln6, a broad hump structure appears in the temperature dependence of the magnetic heat capacity only when the magnetic field is applied parallel to the a axis, which is considered as the magnetic easy axis. The scaling of the temperature dependence of the magnetic heat capacity of the two salts is possible using the parameter of |J_dd|/k_B and therefore the origin of the hump structure is related to the direct magnetic interaction, J_dd, that is dominant in the system. Quite unusual crossover from a three-dimensional ordering to a one-dimensional magnet occurs when magnetic fields are applied parallel to the a axis. A notable anisotropic field-direction dependence against the in-plane magnetic field was also observed in the transition temperature of the bulk superconductivity by the angle-resolved heat capacity measurements. We discuss the origin of this in-plane anisotropy in terms of the 3d electron spin configuration change induced by magnetic fields.