Transport Properties Of Ni-Mn-Ga Thin Films

Magnetic Shape Memory Alloy(MSMA) is a new type of shape memory alloys, which posses not only traditional thermoelasticity shape memory effect that can be controlled by temperature but also magnetic shape memory effect that can be controlled by magnetic field. As a new MSMA material, Ni-Mn-Ga alloy has been received increasing interest due to its large strain and stress, high energy density, high responsive frequency and remarkable magnetoresistance effect.One interesting feature of Ni-Mn-Ga film, which was discovered recently, is the negative magnetoresistance effect. However, there was few knowledge of the transport of nanostructural Ni-Mn-Ga films due to the sensitivity to the composition and preparation technique of the films. Particularly, martensitic transition is so faint in the films that few studies reported the influence of martensite transition on magnetotransport.In this work, we investigated the composition, micro structure and the transport of Ni-Mn-Ga films. All of the films were prepared by electron-beam evaporation techniques. In these films, it can be seen an obvious martensitic transition and a change of resistance as high as 1500% brought by martensite transition. The transition also causes complicate change of the characteristics of magnetoresistance. The magnetoresistance of the austenite can usually be ascribed to the ordinary magnetoresistance. However, the magnetoresistance in martensite can be positive, negative or near zero. Most of the films have the magnetoresistance less than 1%, but some films have as high as 500% magnetoresistance at low temperature. Moreover, there is another transition below 50K in some films, included a possible Mott transition.