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

Ni 1–2 x Mn x Ga x ( x ~ 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 ~ 300–350°C. At higher temperatures a cubic silicide (Mn 12 Ni 4 Si 3 ) was obtained. At room temperature, optimal films with the stoichiometric composition ( x ~ 0.2) showed a ferromagnetic hysteresis behavior characterized by significant in-plane rotation. The coercivity of the films was 310 Oe and temperaturedependent measurements confirmed a Curie temperature, T c ~ 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.