Exchange coupling and thermostability in NiFe/NiMn bilayers

The effects of annealing time and temperature on the exchange coupling betw een ferromagnetic NiFe and antiferromagnetic NiMn layers prepared by magnet ron sputtering were systematically studied. With both increasing annealing temperature and annealing time, the exchange coupling energy J(ex) derived from exchange coupling field H-ex and saturation magnetization M-s, showed an initial increase followed by a decrease. Due to the reduction of Ms resu lting from the interdiffusion across the interfaces during annealing, there is a slight difference between the way J(ex) varies with annealing tempera ture and annealing time and the way H-ex varies. From the evolution of J(ex ), it can be deduced that over annealing, including both annealing for too long time and at too high a temperature, is detrimental to the interfacial exchange coupling. The exchange coupling between NiFe and NiMn layers was v ery stable within an environmental temperature ranging from room temperatur e to about 210 degrees C. The exchange path was checked and the distributio n of blocking temperature T-b was estimated.