Origin of magnetism and quasiparticles properties in Cr-doped TiO$_2$

TL;DR

This study combines advanced computational methods to elucidate the magnetic interactions and quasiparticle properties in Cr-doped TiO₂, revealing how superexchange interactions influence magnetic ground states in different crystal phases.

Contribution

It introduces a comprehensive computational approach combining LSDA+U, superexchange analysis, and GW corrections to accurately describe magnetic states and impurity levels in Cr-doped TiO₂.

Findings

Superexchange interactions determine ferromagnetic or antiferromagnetic coupling in rutile and anatase phases.

GW corrections align impurity states and band gaps with experimental data.

A new mechanism stabilizes ferromagnetism in Cr-doped anatase without F-center exchange.

Abstract

Combining LSDA+$U$ and an analysis of superexchange interactions beyond DFT, we describe the magnetic ground states in rutile and anatase Cr-doped TiO$_2$. In parallel, we correct our LSDA+$U$ ground state through GW corrections ($GW$@LSDA+$U$) that reproduce the position of impurity states and the band gaps in satisfying agreement with experiments. Because of the different topological coordinations of Cr-Cr bonds in the ground states of rutile and anatase, superexchange interactions induce either ferromagnetic or antiferromagnetic couplings of Cr ions. In Cr-doped anatase, this interaction leads to a new mechanism which stabilizes a ferromagnetic ground state, in keeping with experimental evidence, without the need to invoke F-center exchange.