Anisotropic strain fields in granular GaAs:MnAs epitaxial layers: Towards self-assembly of magnetic nanoparticles embedded in GaAs

Abstract

Granular GaAs:MnAs, consisting of MnAs nanoclusters embedded in a GaAs matrix, is a hybrid ferromagnet-semiconductor material with potential applications in information storage, magneto-optical, and spin electronics devices. It can be obtained, through phase separation, by high-temperature annealing of diluted (Ga,Mn)As films grown by molecular-beam epitaxy. The granular material thus obtained exhibits room-temperature ferromagnetism and excellent crystal quality, but the magnetic anisotropy is weak and control of the ordering of the clusters in lateral directions of the film has not been achieved yet. We have investigated the strain state of granular GaAs:MnAs films on GaAs(001) substrates at room temperature by x-ray diffraction. Two-dimensional reciprocal-space maps are presented, including x-ray reflections from the GaAs matrix and from the nanosized MnAs crystallites. Based on the x-ray diffraction results, we propose strategies to guide the assembly of the MnAs precipitates within the GaAs matrix, such that (i) lateral order within the film and (ii) single crystallographic orientation of the precipitates relative to the matrix can be achieved. The approach is based on the use of anisotropies and inhomogeneities in the elastic interaction of the crystallites with the matrix to control the precipitation process.