Origin of magnetic moments in defective TiO2 single crystals

TL;DR

This study demonstrates that ferromagnetism can be induced in pure TiO2 single crystals through oxygen ion irradiation, which creates defect complexes involving Ti$^{3+}$ ions and oxygen vacancies that generate local magnetic moments.

Contribution

It reveals the origin of magnetic moments in irradiated TiO2 by identifying specific defect complexes responsible for ferromagnetism.

Findings

Irradiation induces ferromagnetism in pure TiO2.

Defect complexes involve Ti$^{3+}$ ions and oxygen vacancies.

Ti$^{3+}$ ions provide local magnetic moments.

Abstract

In this paper we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman-scattering, and electron spin resonance spectroscopy, a defect complex, \emph{i.e.} Ti$^{3+}$ ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a local (TiO$_{6-x}$) stretching Raman mode. We elucidate that Ti$^{3+}$ ions with one unpaired 3d electron provide the local magnetic moments.