Annealing effect on the recovery of training effect in FeO/sub x//CoFe polycrystalline systems

Summary form only given. In our previous work (Zhang et al. JMMM vol.235, p.319-328, (2001)), we reported that the training effect observed in iron-oxide/ferromagnet (F) exchange coupled bilayer systems is caused by the combination of locking, releasing, and stabilizing of the net surface moments of the AF grains during the training cycles, and pointed out that the thermal effect also plays some role in the training process. In the same systems we observed some recovery of training effect at room temperature. To investigate this phenomenon we performed an annealing experiment. A sample with the structure of Si(100)/FeO/sub x/(70 nm)/CoFe(5 nm)/Ta(10 nm) after 25 cycles of training was annealed at 70/spl deg/C with a magnetic field applied along the pinned direction up to 32 hours with successive interruptions for the measurement of the exchange bias field H/sub eb/, coercivity H/sub c/ and switching fields H/sub sw//sup +/ (pinned direction) and H/sub sw//sup -/ (opposite direction). The training effect after annealing was confirmed to be similar to the as-deposited state with some difference in detail. The activation energy for the recovering process was estimated to be about 1.13 eV by curve fitting of H/sub sw//sup -/, indicating that the distribution of activation energy responsible for the annealing effect is rather narrow. This is consistent with the report by Hou (1999), in which vacancy relocation model was proposed as a mechanism for changing the effective net surface spin moment of each AF-grain by low temperature annealing. This implies that the thermal switching effect (switching of whole spin configuration in a gain) in training and the thermal effect in recovery is different from each other.