The structural and magnetic properties of MnAs epilayers grown on GaAs(111)B have been investigated by x-ray diffraction and magnetometry. The strain evolution of the epilayer was followed during the phase transition by x-ray diffraction. The results show a high fraction of the alpha ferromagnetic phase at room temperature and an elevated value of the structural phase transition temperature. The system is strongly affected by residual strains that are mainly located inside the beta phase. We attribute this behavior to an increase in the elastic energy density associated with the tight link between epilayer and substrate. It comes out that magnetic and structural properties of MnAs thin films are strongly dependent on the crystallographic relation between epilayer and substrate.
