Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Is altermagnetism in vanadium oxychalcogenides a lost cause?

Bishal Thapa, Po-Hao Chang, Kirill Belashchenko, Igor I. Mazin

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.

Is altermagnetism in vanadium oxychalcogenides a lost cause?

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.
Paper Structure (7 sections, 4 figures, 1 table)

This paper contains 7 sections, 4 figures, 1 table.

Table of Contents

  1. Introduction ---
  2. Crystal and magnetic structure ---
  3. Computational details ---
  4. Intralayer Exchange Coupling ---
  5. Interlayer Coupling and the Bulk Ground State ---
  6. Influence of Charge Doping on Exchange Coupling ---
  7. Conclusions ---

Figures (4)

  • Figure 1: (a) Crystal structure of AV$_{2}$Q$_{2}$O showing octahedra forming prismatic slabs separated by the intercalating A layers. (b) Magnetic lattice viewed along the $c$ axis. Cyan and magenta colors denote V atoms on two magnetic sublattices. $J_1$, $J_{2\alpha}$, $J_{2\beta}$, $J_3$: exchange parameters. (c) AM bulk ordering: all ILL layers are stacked ferromagnetically. (d) AF bulk ordering: ILL layers are stacked antiferromagnetically. A and Q atoms are omitted for clarify in panels (c) and (d). $J_{\perp}$: interlayer magnetic coupling.
  • Figure 2: Magnetic phase diagram in the $(J_{2\alpha}/|J_{1}|,\,J_{2\beta}/|J_{1}|)$ parameter space. The red lines denote the phase boundaries for $J_{3}=0.1|J_1|$. For comparison, black dashed lines show the phase boundaries at $J_3=0$ (note that $J_{3}>0$ expands the AM region). The unlabeled regions are various non-AM phases, as discussed in Ref. chang_inverse_2025.
  • Figure 3: Interlayer exchange coupling $J_{\perp}$ as a function of hole doping $\Delta Q$ (per f.u.). $\Delta Q=0$ corresponds to the stoichiometric composition. The error bars show the difference between the calculations performed with $26\times26\times7$ and $22\times22\times7$$k$-point meshes.
  • Figure 4: Dependence of the intralayer exchange parameters on hole doping $\Delta Q$ (holes per f.u.) for selected compounds.