The effect of the deposition rate on the crystallographic texture, microstructure evolution and magnetic properties in sputter deposited Ni-Mn-Ga thin films

Abstract

The development of crystallographic texture (preferred orientation), structure and microstructure has been investigated and correlated with the magnetic properties of sputter-deposited Ni-Mn-Ga thin films. The overall compositions of the films were strongly dependent on the sputtering power. X-ray diffraction based crystallographic texture measurement and transmission electron microscopy have been performed to examine the preferred orientation and structure of the films. All the films exhibit strong 〈400〉 and 〈220〉 double fiber orientation with no sign of in-plane preferred orientation. The strengthening of 〈400〉 and weakening of 〈220〉 preferred orientation in the films are observed with an increase in sputtering power. The development of the texture in films is mainly governed by the minimization of surface energy and strain energy. All the films exhibit a uniform microstructure with an increase in grain size as the sputtering power increases. An analysis of the magnetic hysteresis of the films revealed that all the films are ferromagnetic in nature, irrespective of the sputtering power. However, coercivity and the saturation field are found to be dependent on the sputtering power, and lead to the crystallographic texture of the films.