# Magnetism study on a frustration-free spatially anisotropic $S$ = 1 square lattice antiferromagnet Ni[SC(NH$_2$)$_2$]$_6$Br$_2$

## TL;DR

This study investigates the magnetic properties of a spatially anisotropic $S$=1 square lattice antiferromagnet Ni[SC(NH$_2$)$_2$]$_6$Br$_2$, revealing long-range order, anisotropic susceptibility, and gapped spin-wave excitations.

## Contribution

First detailed exploration of magnetism in an unfrustrated $S$=1 anisotropic square lattice antiferromagnet with comprehensive thermodynamic and magnetic phase analysis.

## Key findings

- Long-range antiferromagnetic order at 2.23 K
- Evidence of XY anisotropy in the ordered state
- Confirmation of gapped spin-wave dispersion

## Abstract

Magnetism of the $S$ = 1 Heisenberg antiferromagnets on the spatially anisotropic square lattice has been scarcely explored. Here we report a study of the magnetism, specific heat, and thermal conductivity on Ni[SC(NH$_2$)$_2$]$_6$Br$_2$ (DHN) single crystals. Ni$^{2+}$ ions feature an $S$ = 1 rectangular lattice in the $bc$ plane, which can be viewed as an unfrustrated spatially anisotropic square lattice. A long-range antiferromagnetic order is developed at $T \rm_N =$ 2.23 K. Below $T\rm_N$, an upturn is observed in the $b$-axis magnetic susceptibility and the resultant minimum might be an indication for the $XY$ anisotropy in the ordered state. A gapped spin-wave dispersion is confirmed from the temperature dependence of the magnetic specific heat. Anisotropic temperature-field phase diagrams are mapped out and possible magnetic structures are proposed.