Suppression of martensitic phase transition at the Ni2MnGa film surface

We investigated magnetic and structural properties at the surface of epitaxial Ni(2)MnGa(110) Heusler films using x-ray absorption spectroscopy and x-ray magnetic circular dichroism both in transmission and total electron yield mode. The magnetic shape memory films were prepared by dc sputtering from a stoichiometric target onto sapphire substrates at an optimized substrate temperature of 773 K. X-ray diffraction confirms a (110) oriented growth on Al(2)O(3)(11 (2) over bar0) and an austenite to martensite transition at 270-280 K. At the surface the martensitic phase transition and the magnetization are strongly suppressed. The deviation in the surface properties is caused by a Mn deficiency near the surface. (C) 2008 American Institute of Physics.