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We investigated the temperature-dependent magnetoresistance of granular (Ga,Mn)As/MnAs hybrids grown on (100) GaAs in different transport geometries. The observed magnetoresistance effects are much bigger than for a corresponding (Ga,Mn)As reference sample without MnAs nanoclusters. We find that the magnetoresistance effects depend strongly on the chosen transport geometry. When the external field is perpendicular to the sample plane the effects are largest. The smallest effects occur when the external field is in the sample plane and parallel to the current. Furthermore, we have established by ferromagnetic resonance studies that the magnetic properties of the ensemble of ferromagnetic MnAs nanoclusters is similar for the magnetic field orientations studied. Therefore, the observed anisotropy of the magnetoresistance mainly reflects the difference in current path through the sample which leads to a variation of the degree of interaction between the free carriers in the matrix and nanoclusters.

By calculations in the framework of the valence force field method, we show that nitrogen atoms in diluted GaAs 1−x N x tend to align along the [001] direction. In quaternary alloys Ga 1−y In y As 1−x N x this tendency is observed only in "as-grown" samples, while in the annealed samples nitrogen atoms build more energetically favorable bonds with indium. Experimentally observed inhomogeneous strain profiles in these material systems, as well as their dissolution upon annealing, agree qualitatively with results of the calculations.

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