The origin of magnetism in anatase Co-doped TiO₂ magnetic semiconductors

Dilute magnetic semiconductors (DMS) can be tailored by doping a small amount of elements containing a magnetic moment into host semiconductors, which leads to a new class of semiconductors with the functionality of tunable magnetic properties. Recently, oxide semiconductors have attained interests for the possibility of developing room temperature dilute magnetic semiconductors. However, a large number of conflicting results have pointed towards both an intrinsic and extrinsic origin for ferromagnetism. In earlier studies of oxides in relation to DMS, the controversy originated mainly from imprudent conclusions relying on measurements of macroscopic magnetic properties without careful structural studies of secondary phases in the materials under investigation. This thesis describes the results of experiments with a broad set of complementary tools to investigate the origin of ferromagnetism in anatase Co:TiO2, which shows room temperature magnetism and an anomalous Hall effect (AHE).