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

Ni/sub 1-2x/Mn/sub x/Ga/sub x/ (x/spl sim/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/sub g/). The tetragonal martensite structure with a [220] texture was obtained for an optimal T/sub g//spl sim/300-350/spl deg/C. At higher temperatures a cubic silicide (Mn/sub 12/Ni/sub 4/Si/sub 3/) was obtained. At room temperature, optimal films with the stoichiometric composition (x /spl sim/ 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/sub c//spl sim/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/spl deg/C.