Spin-orbit coupled molecular quantum magnetism realized in inorganic solid

Cluster Frustration in the Breathing Pyrochlore Magnet LiGaCr_{4}S_{8}

We present a comprehensive neutron scattering study of the breathing pyrochlore magnet LiGaCr_{4}S_{8}. We observe an unconventional magnetic excitation spectrum with a separation of high- and low-energy spin dynamics in the correlated paramagnetic regime above a spin-freezing transition at 12(2) K. By fitting to magnetic diffuse-scattering data, we parametrize the spin Hamiltonian. We find that interactions are ferromagnetic within the large and small tetrahedra of the breathing pyrochlore lattice, but antiferromagnetic further-neighbor interactions are also essential to explain our data, in qualitative agreement with density-functional-theory predictions [Ghosh et al., npj Quantum Mater. 4, 63 (2019)2397-464810.1038/s41535-019-0202-z]. We explain the origin of geometrical frustration in LiGaCr_{4}S_{8} in terms of net antiferromagnetic coupling between emergent tetrahedral spin clusters that occupy a face-centered-cubic lattice. Our results provide insight into the emergence of frustration in the presence of strong further-neighbor couplings, and a blueprint for the determination of magnetic interactions in classical spin liquids.

All-Inorganic Single-Ion Magnets in Ceramic Matrices

All-inorganic single-ion magnets representing paramagnetic ions incorporated in a crystalline diamagnetic matrix are reviewed. Key results and advantages of this approach in comparison with the common strategy based on molecular metal-organic complexes are considered, and some unsolved problems and future perspectives are discussed.

Behavior of the breathing pyrochlore lattice Ba3Yb2Zn5O11 in applied magnetic field

The breathing pyrochlore lattice material Ba₃Yb₂Zn₅O₁₁ exists in the nearly decoupled limit, in contrast to most other well-studied breathing pyrochlore compounds. As a result, it constitutes a useful platform to benchmark theoretical calculations of exchange interactions in insulating Yb³⁺ magnets. Here we study Ba₃Yb₂Zn₅O₁₁ at low temperatures in applied magnetic fields as a further probe of the physics of this model system. Experimentally, we consider the behavior of polycrystalline samples of Ba₃Yb₂Zn₅O₁₁ with a combination of inelastic neutron scattering and heat capacity measurements down to 75 mK and up to fields of 10 T. Consistent with previous work, inelastic neutron scattering finds a level crossing near 3 T, but no significant dispersion of the spin excitations is detected up to the highest applied fields. Refinement of the theoretical model previously determined at zero field can reproduce much of the inelastic neutron scattering spectra and specific heat data. A notable exception is a low temperature peak in the specific heat at  ∼0.1 K. This may indicate the scale of interactions between tetrahedra or may reflect undetected disorder in Ba₃Yb₂Zn₅O₁₁.