Structure and magnetism of MnAs nanocrystals embedded in GaAs as a function of post-growth annealing temperature.

Self-organized Ga(Mn)As nanoclusters, embedded in GaAs, were formed during post-growth thermal annealing of Ga_1-xMn_xAs layers. Structural and magnetic properties of such composites were systematically studied as a function of the annealing temperature. Small (∼3 nm) Mn-rich zinc-blende Mn(Ga)As clusters, coherent with the GaAs matrix, were formed at the annealing temperature of 500 °C. An increase of the annealing temperature of up to 600 °C led to the creation of 10–20 nm large NiAs-type hexagonal MnAs nanocrystals. Magnetization measurements showed that the MnAs nanoprecipitates were superparamagnetic, with a distribution of blocking temperatures that depended on the MnAs cluster size. Some intermediate paramagnetic clusters (structurally disordered clusters) were also observed. [ABSTRACT FROM AUTHOR]