MoP$_3$SiO$_{11}$: a $4d^3$ honeycomb antiferromagnet with disconnected octahedra

TL;DR

This study reveals the crystal structure and magnetic properties of MoP$_3$SiO$_{11}$, a $4d^3$ honeycomb antiferromagnet with disconnected octahedra, highlighting the role of single-ion anisotropy and spin-orbit coupling.

Contribution

The paper provides the first detailed structural and magnetic characterization of MoP$_3$SiO$_{11}$, emphasizing the significance of single-ion anisotropy in $4d^3$ honeycomb antiferromagnets.

Findings

Rhobohedral space group $R\bar{3}c$ established

Long-range antiferromagnetic order below 6.8 K

Magnon gap of approximately 7 K due to anisotropy

Abstract

We report the crystal structure and magnetic behavior of the $4d^3$ spin-$\frac32$ 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 ($R\bar 3c$) 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 $\mathbf k=0$ observed below $T_N=6.8$ K is a combined effect of the nearest-neighbor in-plane exchange coupling $J\simeq 2.6$ K, easy-plane single-ion anisotropy $D\simeq 2.2 $ K, and a weak interlayer coupling $J_c\simeq 0.8$ K. The 12% reduction in the ordered magnetic moment of the Mo$^{3+}$ ions and the magnon gap of $\Delta\simeq 7$ 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.