Co-occurrence of Superparamagnetism and Anomalous Hall Effect in Highly Reduced Cobalt-Doped RutileTiO2−δFilms

Abstract

We report a detailed magnetic and structural analysis of highly reduced Co doped rutile ${\mathrm{TiO}}_{2-\delta }$ films displaying an anomalous Hall effect (AHE). The temperature and field dependence of magnetization, and transmission electron microscopy, clearly establish the presence of nanosized superparamagnetic cobalt clusters of $\sim 8–10\mathrm{nm}$ size in the films at the interface. The co-occurrence of superparamagnetism and AHE raises questions regarding the use of the AHE as a test of the intrinsic nature of ferromagnetism in diluted magnetic semiconductors.