Control of the setting process in CoFe/IrMn exchange bias systems

The time and temperature dependences of the exchange field achieved by control of the setting conditions in CoFe/IrMn exchange couples have been investigated. This has been achieved by varying the temperature at which the antiferromagnet was set $(TSET)$ and by measuring the time dependence of the exchange field $(Hex)$ at each temperature. The exchange field was observed to vary logarithmically with setting time, indicating that a wide distribution of energy barriers is present in the antiferromagnetic (AF) layer. The results are consistent with an independent AF grain model of exchange bias where the energy barrier distribution to reversal is governed by the grain volume distribution and the temperature dependence of the magnetocrystalline anisotropy. Calculations of the time dependence of the setting process are in good agreement with the grain volume model.