Stress induced martensite in epitaxial Ni-Mn-Ga films deposited on MgO(001)

Biaxial tensile stress in epitaxial Ni52Mn23Ga25 films on MgO(001) was measured at different temperatures using an adapted x-ray stress analysis. A stress of up to 105 MPa originates from different thermal expansions of substrate and film and partially from the substrate-film misfit. The film transforms to twinned orthorhombic martensite at 319 K. The stress increases the martensitic transformation temperature of about 63 K. This is in good agreement with respect to the transformation temperature expected from the composition of the film. The presence of biaxial tensile stress leads to twin boundary selection, hence, there are no twin planes perpendicular to the substrate. (c) 2008 American Institute of Physics.