Magnetization and domain patterns in martensitic NiMnGa films on Si(100) wafer

A series of Ni_51.4Mn_28.3Ga_20.3 films sputter-deposited on Si(100) wafer (with 500 nm thick buffer layer of SiN _x) and annealed at 800°C for 1h. are investigated with respect to their transformation behavior and magnetic properties. The film thickness, d, varies from 0.1 to 5.0 μm. Resistivity measurements reveal martensitic transformation above room temperature for all the films except for 0.1 μm-thick film which is transforming at much lower temperature. The magnetic characteristics of martensitic films such as susceptibility and anisotropy field extracted from the in-plane and out-of-plane magnetization curves show film thickness dependence likewise Curie temperature obtained from the resistivity curves. The surface topography and micromagnetic structure are studied by scanning probe microscopy. A stripe magnetic domain pattern featuring a large out-of-plane magnetization component is found in the films. The domain width, δ, depends on the film thickness, d, as δ - √d.