Competing magnetic interactions in spin-1/2 square lattice: hidden order in Sr$_2$VO$_4$

TL;DR

This study combines theoretical methods to reveal complex magnetic interactions and hidden order phenomena in Sr$_2$VO$_4$, suggesting a potential spin-liquid state at low temperatures.

Contribution

It uncovers a highly competing exchange interaction landscape and a strong spin-compass anisotropy, providing insights into the hidden order and magnetic properties of Sr$_2$VO$_4$.

Findings

Identified a single-stripe antiferromagnetic ground state.

Discovered strong two-site spin-compass exchange anisotropy.

Proposed the possibility of a spin-liquid phase at low temperatures.

Abstract

With decreasing temperature Sr$_2$VO$_4$ undergoes two structural phase transitions, tetragonal-to-orthorhombic-to-tetragonal, without long-range magnetic order. Recent experiments suggest, that only at very low temperature Sr$_{2}$VO$_{4}$ might enter some, yet unknown, phase with long-range magnetic order, but without orthorhombic distortion. By combining relativistic density functional theory with an extended spin-1/2 compass-Heisenberg model we find an antiferromagnetic single-stripe ground state with highly competing exchange interactions, involving a non negligible inter-layer coupling, which places the system at the crossover between between the XY and Heisenberg picture. Most strikingly, we find a strong two-site "spin-compass" exchange anisotropy which is relieved by the orthorhombic distortion induced by the spin stripe order. Based on these results we discuss the origin of the hidden order phase and the possible formation of a spin-liquid at low temperatures.