Interlayer coupling dependent magnetic properties in amorphous and nanocrystalline FeTaC based multilayer thin films

We report systematic studies on the effects of heat treatment, the number of multilayers and temperature on interlayer coupling dependent magnetic properties in amorphous and nanocrystalline ([FeTaC(y nm)/Ta(1 nm)](n=1-4)/FeTaC(y nm)/substrate) multilayer structured thin films fabricated directly on thermally oxidized Si substrate at ambient temperature and post annealed at different elevated temperatures (T-A). As-deposited films and the films annealed at 200 degrees C exhibit an amorphous structure. With an increase in TA. 300 degrees C, the nucleation of fine nanocrystals in a residual amorphous matrix appears and a fraction of such nanocrystals increases with increasing T-A. The changes in the microstructure modify the interlayer coupling between FeTaC ferromagnetic layers due to the release of stress accumulated during film deposition and enhanced interface roughness with increasing TA. As a result, a change in the shape of the magnetic hysteresis (M-H) loop and multistep magnetization reversal process, where the number of steps in the M-H loop, their nature and positions strongly depend on the number of multilayers, T-A and temperature, were observed. As-deposited films and the films annealed at 200 degrees C exhibit multistep magnetization reversal behavior only at temperatures below 80 K, but the films annealed above 200 degrees C show such multistep reversal behavior even at 300 K. This causes an unusual variation of temperature-dependent coercivity in these multilayer films having different microstructures. Furthermore, the coercivity due to individual or collective switching between FeTaC layers in these films varies unusually and is substantially influenced by the bottom FeTaC layer grown directly on the substrate. The observed results were discussed on the basis of variation in interlayer coupling with the multilayer structure, post annealing conditions and temperature. This provided evidence of controlling the soft magnetic properties and comprehensive study on the multistep magnetization reversal behavior in multilayer structured FeTaC based thin films.