Annealing effect on structural and magnetic properties of Ta/Cu/FeMn/Co/FeMn/Ta thin film structures

We report on the annealing effect on the structural and magnetic properties of Ta5nm/Cu5nm/FeMn8nm/Co8nm/FeMn8nm/Ta5nm samples prepared by sputtering, on silicon substrate, at room temperature. For the as-deposited samples the interfacial exchange anisotropy field (He) between the Co and FeMn layers is about 95 Oe. It increases sensitively with annealing to reach a maximum value of 135 Oe at 240 °C annealing temperature. Above this temperature, we observe a strong decrease of He, down to 90 Oe after annealing at 280 °C, and an increase of 50% of the saturation magnetization. In order to understand the effect of the annealing on the magnetic properties, we performed a detailed structural analysis by means of Rutherford back scattering spectroscopy (RBS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). All these techniques attribute the large changes in the magnetic properties to the formation of a new ferromagnetic FeMnCo phase at the FeMn/Co interfaces