Phase-transition-induced residual strain in ferromagnetic MnAs films epitaxially grown on GaAs(001)

We investigate the atomic interface structure and the residual strain state of ferromagnetic alpha (hexagonal) MnAs layers on cubic GaAs(001) by means of high-resolution transmission electron microscopy and electron diffracti on. Despite the different symmetries of the adjacent planes at the heteroin terface and the large and orientation-dependent lattice mismatch, the hexag onal MnAs grows epitaxially on GaAs(001) with the (1 (1) over bar .0) prism plane parallel to the cubic substrate. The atomic arrangement at the inter face, which is defined by the accommodation of the large lattice mismatch, explains this extreme case of heteroepitaxial alignment. The anisotropic re sidual strain distribution is discussed with respect to the particular proc ess of lattice misfit relaxation in the presence of the ferromagnetic phase transition. (C) 2001 American Institute of Physics.