Thickness dependent magnetic properties of amorphous FeTaC films

Abstract

We report on the study of thickness and temperature dependent magnetic properties of amorphous FeTaC (t = 20–200 nm) thin films prepared on thermally oxidized Si substrate at ambient temperature. Room temperature coercivity remains constant (∼1.5 Oe) for t between 20 and 50 nm, but increases rapidly (>18 Oe) when t > 50 nm. Also, the shape of M-H loop changes from rectangular to flat loop with increasing film thickness; and at larger thicknesses (>50 nm), the central range of constant slope in the flat loop extended largely along with the enlargement of hysteresis around the origin. This is mainly due to the development of perpendicular anisotropy with increasing the film thickness causing a transition from in-plane orientations of the spins to a magnetic stripe domain structure, which degrades the magnetic properties at larger thickness. Low temperature thermomagnetization curves obtained under zero-field-cooled (ZFC) and field-cooled (FC) conditions depicts a bifurcation between ZFC and FC data at larger thickness films. With decreasing t, the bifurcation point shifted to lower temperatures and almost disappeared for t ≤ 50 nm. On the other hand, the high temperature magnetization data reveal a considerable increase in Curie temperature with decreasing film thickness and the magnetic susceptibility critical exponent γ exhibits a thickness dependent behavior. The observed results are discussed on the basis of two-layer model, and the development of perpendicular anisotropy and magnetic disorder with increasing FeTaC film thickness.