Magnetic Properties, Structure and Shape-Memory Transitions in Ni–Mn–Ga Thin Films Grown by Ion-Beam Sputtering

Ni1 2 Mn Ga ( 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 ( ). The tetragonal martensite structure with a (220) texture was obtained for an optimal 300–350 C. At higher temperatures a cubic silicide (Mn12Ni4Si3) was obtained. At room temperature, optimal films with the stoichiometric composition ( 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, 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 C.