Thickness dependence of magnetic and structural properties in Fe80Ga20 thin films

Abstract

This work focuses on the effect of film thickness on the microstructural and magnetic properties of polycrystalline Fe80Ga20 films of different thickness (20 nm≤t≤200 nm) fabricated on Si⟨100⟩ substrates. From x-ray diffraction, a ⟨110⟩ texture was normal to the film plane in all films. For all film thicknesses, the lattice constant perpendicular to the film plane was less than the bulk, and first decreased and then increased toward the bulk value with increasing t. From atomic force microscopy data, both surface roughness and grain size were found to increase with film thickness. Using the Villari effect, the effective magnetostriction constant λeff was measured. Using the Szymczak model, it was found that λbulk=91±5 ppm, close to the bulk isotropic polycrystalline value (λiso=98 ppm). The surface magnetostriction λs contribution to λeff was found to be −1065±271 ppm nm. It was found that the 20 nm thick film had weak uniaxial anisotropy, while all the other films were magnetically isotropic. An extension of Néel’s model to saturation field showed that the experimental data obeyed this model and the surface term affected the effective saturation field (Hseff) significantly.