MoP3SiO11 : A 4d3 honeycomb antiferromagnet with disconnected octahedra

Abstract

We report the crystal structure and magnetic behavior of the 4d 3 spin-3/2 silicophosphate MoP 3 SiO 11 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 (R 3c) along with the geometrically perfect honeycomb lattice of the Mo 3+ ions residing in disconnected MoO 6 octahedra. Long-range antiferromagnetic order with the propagation vector k = 0 observed below T N = 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 J c 0.8 K. The 12% reduction in the ordered magnetic moment of the Mo 3+ ions and the magnon gap of 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 4d 3 honeycomb antiferromagnets despite their nominally quenched orbital moment.

Theoretical analysis of single-ion anisotropy in $d^3$ Mott insulators

“…Since we have used both SOC and trigonal distortion smaller than Hund's coupling, this theory is more applicable to 3d 3 than 5d 3 systems, where J eff = 3/2 may be a better starting point than S=3/2 spin states. Recent works [37][38][39] of 5d 3 have shown that in these systems there is a large spin gap. We propose that this may be relevant to the atomic SOC discussed in this work.…”