Thermal stability of low dose Ga⁺ ion-irradiated magnetic tunnel junctions

The thermal stability of low dose Ga⁺ ion-irradiated IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction (MTJ) was investigated using a vibrating sample magnetometer at room temperature and compared with that of the non-irradiated one. The results show that not only does the loop become broad both in the pinned FM layer and in the free FM layer but also there is an obvious larger shift in the pinned FM layer after irradiated at a dose of 1×10¹³ ions/cm² Ga⁺ ions. The training effect becomes more legible after performing a low dose irradiation. In both the non-irradiated and the low dose Ga⁺ irradiated MTJs the thermal activation has been observed and holding the films at negative saturation of the pinned FM layer for up to 28 h results in a decrease of the exchange bias field (H_ex). However, the absolute value of H_ex of the irradiated MTJ is always larger than that of the non-irradiated one in the experimental period of time, although the H_ex of the irradiated MTJ decreases a little faster.