We report the crystal structure and magnetic behavior of the 4d3 spin-23 silicophosphate MoP3SiO11 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 (R3ˉc) along with the geometrically perfect honeycomb lattice of the Mo3+ ions residing in disconnected MoO6 octahedra. Long-range antiferromagnetic order with the propagation vector k=0 observed below TN=6.8 K is a combined effect of the nearest-neighbor in-plane exchange coupling J≃2.6 K, easy-plane single-ion anisotropy D≃2.2 K, and a weak interlayer coupling Jc≃0.8 K. The 12% reduction in the ordered magnetic moment of the Mo3+ ions and the magnon gap of Δ≃7 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 4d3 honeycomb antiferromagnets despite their nominally quenched orbital moment.
@article{arxiv.2107.08618,
title = {MoP$_3$SiO$_{11}$: a $4d^3$ honeycomb antiferromagnet with disconnected octahedra},
author = {Danis I. Badrtdinov and Lei Ding and Clemens Ritter and Jan Hembacher and Niyaz Ahmed and Yurii Skourski and Alexander A. Tsirlin},
journal= {arXiv preprint arXiv:2107.08618},
year = {2021}
}