Formation of Co nanoclusters in epitaxial Ti_{0.96} Co_{0.04} O_2 thin films and their ferromagnetism

TL;DR

This study investigates how varying oxygen pressure during growth influences cobalt cluster formation in TiO2 films, leading to room-temperature ferromagnetism due to cobalt clustering, confirmed by electron microscopy.

Contribution

It demonstrates the direct link between cobalt clustering and ferromagnetism in epitaxial TiO2 films, highlighting the role of growth conditions in magnetic properties.

Findings

Lower PO2 promotes cobalt cluster formation.

Cobalt clusters induce room-temperature ferromagnetism.

Structural changes correlate with magnetic behavior.

Abstract

Anatase Ti0.96Co0.04O2 films were grown epitaxially on SrTiO3 (001) substrates by using plused laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, PO2, during the growth was systematically varied. As PO2 decreased, the growth behavior was changed from a 2-dimensional layer-by-layer-like growth to a 3-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscopie studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO2 films.