Effect of heat treatment and spacer layer driven interlayer coupling in laminated type FeTaC thin films

摘要

We report systematic studies on the effect of heat treatment and spacer layer thickness (x) on structural and temperature dependent magnetic properties of laminated [FeTaC (50 nm)/Ta (x nm)]_3/FeTaC (50 nm) thin films. All the films were deposited directly on oxidized Si substrate using magnetron sputtering technique at ambient temperature and post annealed at different temperatures. As-deposited films and the films annealed at 200 ℃ exhibit amorphous structure. With increasing annealing temperature (T_A), nucleation of α-Fe nanocrystals at 300 ℃ and well grown α-Fe nanocrystals at 400 ℃ were observed. The shape of room temperature magnetic hysteresis (M-H) loops and the magnetization reversal behavior of individual FeTaC layer in the laminated films depend strongly on T_A and x. Coercivity (H_C) decreases largely from 24 Oe for as-deposited single layer film to 0.02 Oe for the multilayer films annealed at 200 ℃, but increases with the further increase in T_A. M-H loops measured at different temperatures reveal strong temperature dependent multistep magnetization reversal process, where the number, nature and position of the steps in the M-H loops essentially vary with temperature, x and T_A. This results unusual variation of H_C with temperature and exhibit a broad minimum in H_C(T) curve for the films annealed at 300 ℃. The minimum point in H_C(T) curve depends on × and shifts to lower temperature with increasing x. On the other hand, high temperature thermomagnetization data show a strong (significant) variation of Curie temperature with T_A (x). The observed results are discussed on the basis of variation in interlayer couplings with respect to x, T_A, and temperature driven structural and interfacial properties.