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

Ni1-2xMnxGax (x similar to 0.2 and 0.25) alloys in thin film form were prep ared 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 f or an optimal T-g similar to 300-350 degreesC. At higher temperatures a cub ic silicide (Mn12Ni4Si3) was obtained. At room temperature, optimal films w ith the stoichiometric composition (x similar to 0.2) showed a ferromagneti c hysteresis behavior characterized by significant in-plane rotation. The c oercivity of the films was 310 Oe and temperature-dependent measurements co nfirmed 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 sit u heating experiments to transforms to the cubic austenite phase at 500 deg reesC.