Appearance of room temperature ferromagnetism in Cu-doped TiO$_{2-\delta}$ films

TL;DR

This paper reports the discovery of significant room temperature ferromagnetism in Cu-doped TiO₂ thin films, highlighting the crucial role of oxygen vacancies and providing both experimental and theoretical insights.

Contribution

It demonstrates unexpected room temperature ferromagnetism in nonmagnetic Cu-doped TiO₂ films and emphasizes the importance of oxygen vacancies for this magnetic behavior.

Findings

Large magnetic moment of about 1.5 μ_B per Cu atom.

Oxygen vacancies are essential for ferromagnetism.

Cu doping promotes oxygen vacancy formation.

Abstract

In recent years there has been an intense search for room temperature ferromagnetism in doped dilute semiconductors, which have many potentially applications in spintronics and optoelectronics. We report here the unexpected observation of significant room temperature ferromagnetism in a semiconductor doped with nonmagnetic impurities, Cu-doped TiO$_2$ thin films grown by Pulsed Laser Deposition. The magnetic moment, calculated from the magnetization curves, resulted surprisingly large, about 1.5 $\mu_B$ per Cu atom. A large magnetic moment was also obtained from ab initio calculations using the supercell method for TiO$_2$ with Cu impurities, but only if an oxygen vacancy in the nearest-neighbour shell of Cu was present. This result suggests that the role of oxygen vacancies is crucial for the appearance of ferromagnetism. The calculations also predict that Cu doping favours the formation of oxygen vacancies.