Evaluation of Compensated Magnetism in La$_2$VCuO$_6$: Exploration of Charge States

TL;DR

This study uses ab initio calculations to explore charge and spin configurations in La$_2$VCuO$_6$, revealing a near-degenerate spin-compensated half-metal and a non-magnetic band insulator as the ground state.

Contribution

It identifies and compares two close-energy charge and spin states in La$_2$VCuO$_6$, highlighting the importance of structural distortions and Jahn-Teller effects in determining the ground state.

Findings

The spin-compensated half-metal state is stable at moderate U values.

The non-magnetic band insulator is the ground state at small and moderate U.

Structural distortions significantly influence the energy differences between states.

Abstract

We present an ab initio study of double perovskite La$_2$VCuO$_6$, which was one of the earliest compounds suggested as a potential compensated half-metal. Two charge and spin configurations close in energy have been identified. (i) The originally envisioned spin-compensated V$^{4+}$:d$^1$/Cu$^{2+}$:d$^1$ configuration is comprised of antialigned S=1/2 cations. This state is a spin-compensated half-metal for moderate values of U (the on-site Coulomb repulsion strength on the metal ions) and is insulating for larger values of U. (ii) An unanticipated non-magnetic solution V$^{5+}$:d$^0$/Cu$^{+}$:d$^{10}$ consists of an empty- and a full-shell ion, both spherically symmetric, that leads to a band insulator. This ionic band insulator is calculated to be the ground state at small and moderate values of U. The different distortions of the perovskite structure that occur for each state are central in determining the energy differences. Treating the Cu$^{2+}$ Jahn-Teller distortion self-consistently is particularly important for the magnetic solution.