Intrinsic Ferromagnetism in the Diluted Magnetic Semiconductor Co:TiO$_2$

TL;DR

This study demonstrates that Co:TiO$_2$ thin films grown under low oxygen partial pressure exhibit intrinsic ferromagnetism, confirmed by experimental and theoretical analyses, establishing it as a true diluted magnetic semiconductor.

Contribution

The paper provides experimental and theoretical evidence that low oxygen partial pressure during growth induces intrinsic ferromagnetism in Co:TiO$_2$ thin films, resolving previous ambiguities.

Findings

Low oxygen partial pressure leads to homogeneous, fully magnetic films.

Cobalt clustering occurs at low deposition rates or postannealing.

First principles calculations support the role of oxygen pressure in ferromagnetism.

Abstract

Here we present a study of magnetism in \CTO\ anatase films grown by pulsed laser deposition under a variety of oxygen partial pressures and deposition rates. Energy-dispersive spectrometry and transition electron microscopy analyses indicate that a high deposition rate leads to a homogeneous microstructure, while very low rate or postannealing results in cobalt clustering. Depth resolved low-energy muon spin rotation experiments show that films grown at a low oxygen partial pressure ($\approx 10^{-6}$ torr) with a uniform structure are fully magnetic, indicating intrinsic ferromagnetism. First principles calculations identify the beneficial role of low oxygen partial pressure in the realization of uniform carrier-mediated ferromagnetism. This work demonstrates that Co:TiO$_2$ is an intrinsic diluted magnetic semiconductor.