Effect of isothermal crystallization in antiferromagnetic IrMn on the formation of spontaneous exchange bias

Abstract

Recently, a spontaneous exchange bias (SEB) driven by the isothermal crystallization of the antiferromagnetic IrMn layer has been reported in IrMn/FeCo bilayer. However, the key factors to determine the magnitude of SEB have not been clearly understood yet. Here, we investigate the effect of isothermal crystallization in IrMn layer on the formation of SEB in IrMn/CoFeB bilayer through preparing the samples with different degrees of isothermal crystallization in IrMn layer. The SEB is negligible in the sample with more structure-stable IrMn layer, confirming that the isothermal crystallization of IrMn plays a crucial role in the formation of SEB. However, the SEB field does not change significantly with the free-relaxation time of IrMn/CoFeB bilayers or IrMn layer. These results indicate that a slight degree of isothermal crystallization in IrMn layer is sufficient to induce a large SEB in IrMn/CoFeB bilayer. Our results not only confirm the newly reported SEB driven by the isothermal crystallization in IrMn layer but also clarify the key factor to control the magnitude of SEB.