MoP3SiO11: A4d3 honeycomb antiferromagnet with disconnected octahedra

Abstract

We report the crystal structure and magnetic behavior of the spin- silicophosphate studied by high-resolution synchrotron x-ray diffraction, neutron diffraction, thermodynamic measurements, and ab initio band-structure calculations. Our data revise the crystallographic symmetry of this compound and establish its rhombohedral space group () along with the geometrically perfect honeycomb lattice of the ions residing in disconnected octahedra. Long-range antiferromagnetic order with the propagation vector observed below K is a combined effect of the nearest-neighbor in-plane exchange coupling K, easy-plane single-ion anisotropy K, and a weak interlayer coupling K. The 12% reduction in the ordered magnetic moment of the ions and the magnon gap of K induced by the single-ion anisotropy further illustrate the impact of spin-orbit coupling on the magnetism. Our analysis puts forward single-ion anisotropy as an important ingredient of honeycomb antiferromagnets despite their nominally quenched orbital moment. ©2021 American Physical Society