Photoemission study of the (100) surface of Ni2MnGa and Mn2NiGa ferromagnetic shape memory alloys

The (1 0 0) surface of Ni2MnGa and Mn2NiGa ferromagnetic shape memory alloys have been studied by photoelectron spectroscopy and low energy electron diffraction (LEED). It is shown that by sputtering and annealing, it is possible to obtain a clean, ordered and stoichiometric surface that shows a four-fold 1 x 1 LEED pattern at room temperature. For both Ni2MnGa and Mn2NiGa, the surface becomes Ni-rich and Mn deficient after sputtering. However, as the annealing temperature is increased Mn segregates to the surface and at sufficiently high annealing temperature the Mn deficiency caused by sputtering is compensated. The (1 0 0) surface of Ni2MnGa is found to have Mn-Ga termination. The valence band spectra of both Ni2MnGa and Mn2NiGa exhibits modifications with surface composition. For the stoichiometric surface, the origin of the spectral shape of the valence band is explained by calculations based on first principles density functional theory. (C) 2009 Elsevier B.V. All rights reserved.