Influence of Ga+ ion irradiation on thermal relaxation of exchange bias field in the IrMn-based magnetic tunnel junctions

The IrMn/CoFe/AlOx/CoFe magnetic tunnel junctions (MTJs) were deposited by magnetron sputtering on the surfaces of thermally oxidized Si substrates. The thermal relaxation of both non-irradiated and Ga+ ion irradiated IrMn/CoFe/AlOx/CoFe MTJs has been investigated by means of holding the films in a negative saturation field. As the ion dose increases the exchange bias field shows a maximum at a dose of 1×1013 ions/cm2, resulting from the change of interface roughness induced by irradiation. The irradiation-induced intermixing at the interface of free ferromagnetic (FM) layer and Ta cap layer as well as the Ga+ implantation into free FM layer causes the decrease of the magnetization of free FM layer. The results also showed that exchange bias field decreases with increasing period of holding time for both non-irradiated and Ga+ ion irradiated MTJs, which is owing to the immediate nucleation of reversed AF domains after the reverse field is applied driven by thermal activation over an energy barrier distribution. With ion dose increasing the thermal stability of Hex is enhanced.