Suppression of martensitic phase transition at the Ni2MnGa film surface

We investigated magnetic and structural properties at the surface of epitaxial Ni2MnGa(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 Al2O3(110) 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