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Random arrangements of ferromagnetic MnAs nanoclusters were deposited on (111)B-GaInAs surfaces by standard metal-organic vapor-phase epitaxy (MOVPE). Ordered arrangements of MnAs nanoclusters and cluster chains were obtained by selective-area MOVPE on prepatterned (111)B-GaAs substrates. This new method enables one to control the arrangement of nanoclusters in the growth process offering interesting opportunities to tune the properties of individual MnAs clusters as well as the interaction between the carriers in the surrounding semiconductor matrix and the clusters. The magnetic anisotropy of the MnAs clusters was investigated by magnetic force microscopy and ferromagnetic resonance measurements. The in-plane magnetic anisotropy is mainly determined by the interplay of cluster shape and magnetocrystalline anisotropy while the hard magnetic axis of the clusters is perpendicular to the sample plane independent of cluster shape. The magnetotransport measurements demonstrate that the cluster arrangements strongly influence the transport properties. [ABSTRACT FROM AUTHOR]

The angle-dependent behavior of the magneto-resistance of a series of low-temperature molecular beam epitaxy grown Ga0.98Mn0.02As samples on (311)A-GaAs-substrates is studied. The samples are annealed at different temperatures in a range from 300 °C to 500 °C, which leads to a redistribution of the manganese in the sample and finally to the formation of MnAs clusters. As a consequence, the angle-dependence of the magneto-resistance changes with increasing annealing temperature and vanishes finally at an annealing temperature of 400 °C. The observed anisotropy of the magneto-resistance can be correlated with the magnetic anisotropy of the magnetization. The parameters describing this magnetic anisotropy and their changes due to annealing are extracted from the experimental magneto-resistance data by a fitting procedure. The magnetocrystalline anisotropy of the samples can be described by the sum of cubic and uniaxial contributions. The former are not affected by the annealing whereas the latter change considerably. [ABSTRACT FROM AUTHOR]