Magnetic properties, structure and shape-memory transitions in Ni-Mn-Ga thin films grown by ion-beam sputtering

Abstract

Ni1-2xMnxGax (x similar to 0.2 and 0.25) alloys in thin film form were prepared by ion-beam sputtering from alloy targets. For Si(001) substrates the structure/texture of the films are a function of the growth temperature (T-g). The tetragonal martensite structure with a (220) texture was obtained for an optimal T-g similar to 300-350 degreesC. At higher temperatures a cubic silicide (Mn12Ni4Si3) was obtained. At room temperature, optimal films with the stoichiometric composition (x similar to 0.2) showed a ferromagnetic hysteresis behavior characterized by significant in-plane rotation. The coercivity of the films was 310 Oe and temperature-dependent measurements confirmed a Curie temperature, T-c similar to 340 K. At room temperature the films show a modulated 7M martensite structure which was observed in in situ heating experiments to transforms to the cubic austenite phase at 500 degreesC.