Is altermagnetism in vanadium oxychalcogenides a lost cause?

TL;DR

This study systematically examines vanadium oxychalcogenides with ILL structure, revealing that most are not altermagnetic due to weak interlayer coupling, with CsV2Te2O being a notable exception, and doping does not alter their magnetic states.

Contribution

The paper provides a comprehensive analysis of the magnetic properties of the AV2Q2O family, clarifying the conditions under which altermagnetism can exist in these compounds.

Findings

Most compounds favor antiferromagnetic order due to weak interlayer coupling.

CsV2Te2O is identified as a potential altermagnet.

Doping does not significantly change the magnetic ground state.

Abstract

Vanadium-based oxychalcogenide compounds with the inverse Lieb-lattice (ILL) structural pattern have recently been proposed as candidate altermagnets (AM). However, early studies postulated ferromagnetic interlayer coupling, a critical requirement for preserving the bulk AM state. Here we present a systematic survey of the complete AV2Q2O family (A = K, Rb, Cs; Q = S, Se, Te) in terms of their magnetic ordering and interlayer coupling. While intralayer exchange interaction favors AM ordering in a single ILL layer across the entire family, the relatively weak interlayer coupling in most cases favors Kramers-degenerate antiferromagnetic order with a doubled magnetic unit cell. This means that most stoichiometric bulk materials, including the previously proposed candidate KV2Se2O, are not altermagnetic, with CsV2Te2O being the only exception. Using hole doping to simulate alkali vacancies, we show that realistic deviations from stoichiometry do not change the magnetic ground state in these compounds.