Microstructure evolution and magnetic properties of nanocrystalline Ni75Fe25 thin films: Effects of substrate and thickness

Permalloy (Py) thin films were evaporated from nanocrystalline soft Ni₇₅Fe₂₅ powder onto glass and Al₂O₃ substrates. The thicknesses of these films range from 16 nm to 250 nm. The as deposited films were characterized by grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and vibrating sample magnetometry (VSM). From the GIXRD spectra, we have shown that the films are amorphous for the thinner films. However, for the thicker films, a polycrystalline FCC structure is present. For the intermediate thicknesses, the nature of substrate determines the texture of the films. The SEM micrographs indicate that the nature of substrate influences on the morphology and grains size of Py films. From AFM observations, the nanocrystalline nature of the grains is evidenced. Hysteresis loops reveals the ferromagnetic character of Py films. We have shown that the values of coercive field, H_c, generally, decrease with increasing thickness. Moreover, the H_c values are higher for films deposited onto a Al₂O₃ substrate than those on the glass substrate. The nature of substrate and thickness seems to influence the magnetic properties of Py films. A correlation between these physical properties will be established and discussed.