Structural and magnetic properties of (Ga,Mn)N layers grown on SiC by reactive molecular beam epitaxy

Incorporation of Mn into hexagonal GaN does not lead to ferromagnetic semiconductors, as predicted, but to insulating spin glass materials. Structural characterization by high-resolution transmission electron microscopy reveals that samples with Mn content below 10% are uniform ternary alloys, while in samples with higher Mn content we find Mn-rich clusters which are embedded in the (Ga,Mn)N alloy matrix. At low temperature (<10 K) the magnetic behavior of the samples is similar showing antiferromagnetic characteristics with a spin-glass transition. However, the samples with higher Mn content additionally exhibit ferromagnetic properties even far above room temperature. This ferromagnetism originates from Mn-rich clusters in the ternary alloy.