Co-occurrence of superparamagnetism and anomalous hall effect in highly reduced cobalt-doped rutile TiO_2-δ films

Abstract

We report a detailed magnetic and structural analysis of highly reduced Co doped rutile TiO_2-δ 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 ~8-10 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.