High- TC ferromagnetism in diluted magnetic semiconducting GaN:Mn films

Wurtzite GaN:Mn films with an extremely high Curie temperature of around 940 K and Mn concentration of only 3-5% are successfully grown on sapphire substrates by molecular beam epitaxy. Magnetization measurements are carried out using magnetic fields of up to 7 T parallel to the film surface. The magnetization process reveals the coexistence of ferromagnetic and paramagnetic contributions at low temperatures, with characteristic ferromagnetic magnetization at high temperatures. The observed transport characteristics demonstrate a close relation between magnetism and impurity conduction. The double exchange mechanism of the Mn-impurity band is presented as a possible model for the high- T_C ferromagnetism in GaN:Mn.