Micromechanics of MnAs nanocrystals embedded in GaAs

The full strain state at room temperature of MnAs nanocrystals embedded in a GaAs matrix (GaAs:MnAs) is obtained through x-ray diffraction mapping of the GaAs:MnAs reciprocal space, including x-ray reflections from the nanosized MnAs crystallites. The constrained MnAs clusters are found to hold remarkably large and anisotropic strain. Based on the room-temperature experimental results, Eshelby's 'equivalent-inclusion' concept is used to predict the thermal variation of the cluster lattice parameters in the temperature range from -50 up to 300 deg. C, in particular, across the MnAs magnetostructural phase transition. Strain-driven grain-boundary-mediated rotation and/or (imperfect) oriented attachment of MnAs clusters appear to be operative mechanisms of deformation and particle growth in granular GaAs:MnAs films.