Paramagnetic and ferromagnetic resonance studies on dilute magnetic semiconductors based on GaN

Magnetic resonance studies were preformed on the dilute magnetic semiconductor Gd : GaN. In samples grown by molecular beam epitaxy resonances were observed at temperatures below 50 K. The temperature dependence of the resonance field and the line width suggest a ferromagnetic origin. No similar signals were found in Gd implanted samples even for a Gd concentration ten times higher. At temperatures close to 5 K additional signals were observed near g = 2 in these samples. They are superimposed by a strong substrate signal which is observable in all samples and is attributed to nitrogen donors on sites of different symmetry in the SiC substrate crystal. Different possible explanations of our findings are discussed with special regard to a model suggesting magnetically polarized spheres of influence. By means of magnetic resonance we can not corroborate ferromagnetism at room temperature in Gd:GaN as suggested by SQUID data.