Study on ferromagnetic shape memory alloy Ni–Mn–Ga films

Abstract

The Ferromagnetic Shape Memory Alloy (FSMA) Ni–Mn–Ga films have been prepared by ECR DC magnetron sputtering respectively on unheated NaCl single crystal, Cu, glass and Si wafer. It is found that the optimal parameters for Ni–Mn–Ga film formation are as follows: 22.5 W sputtering power, 60 mm between target and substrate, 0.1 Pa Ar 2 pressure. The films have been characterized by XRD, SEM, AFM and other techniques. There are a large number of fine grains on substrates which were formed by sputtering particles gathering. Ni–Mn–Ga film is typical nucleation growth and development. By comparison of morphology of films on different substrates, it indicates that the roughness of films is greatly affected by substrates. After heat treatment, most of the films are more uniform and compact. But the film on NaCl is broken up due to the different expansion coefficient of film and substrate. It did not occur on Cu and Si wafers. The result of X-ray diffraction indicates that the annealed films are crystalline and most orient to (022). The average crystalline grain size perpendicular to (022) lattice face crystal plane is about 8.503 nm, while its lattice deformation rate is about 1.36%. The strain of Ni–Mn–Ga film induced by magnetic field was tested. Negative 85 ppm was got when applying magnetic field about 13 koe paralleled to film surface. The standard indentation test was employed to Ni–Mn–Ga film with thickness about 400 nm. Elastic modulus of film is calculated as 3.79 GPa while hardness is 252.92 MPa.