Transformation behavior of Ni–Mn–Ga thin films

The transformation behavior of Ni–Mn–Ga submicron polycrystalline thin films was investigated with respect to target composition, different substrates, annealing temperature and film thickness. Two series of thin films (A and B) with thicknesses ranging from 0.1 to 5 µm were deposited onto alumina ceramic, poly-vinyl alcohol (PVA), quartz and glass by the RF magnetron sputtering technique. The use of the targets of Ni 49.5 Mn 28.0 Ga 22.5 and Ni 52 Mn 24 Ga 24 facilitated the formation of 10M and 14M martensitic structures for heat treated films A and B, respectively. Magnetization curves and temperature dependences of resistivity demonstrated anomalies and features typical for the bulk Heusler alloys exhibiting both martensitic and ferromagnetic transformations. The transformation temperatures and distribution of magnetic moments were found to be dependent on the film thickness. A magnetoresistance ratio of 1.5% was achieved at a maximum field of 1.5 T at room temperature.