Three-dimensional numerical calculations based on the finite element method are performed to calculate the increase of temperature caused by Joule heating during the current-induced magnetization switching of an MgO-based magnetic tunnel junction. The increase of temperature is found to be significantly large (the maximum being 145K) at critical conditions for the current-induced magnetization switching. The temperature increase also differs greatly, depending on the critical condition, requiring a correction in calculating the thermal stability parameter using the Slonczewski equation. After the correction, the thermal stability parameter increases substantially from 67 to 76.

Si/SiO 2 /Ta/NiFe/Mn-Ir/CoFe/NOL/CoFe/Al-O/CoFe/NiFe/Ta bottom conventional (without nano-oxide layer, NOL) and specular (with NOL) MTJs were prepared by DC magnetron sputtering methods. In the case of a conventional MTJ, the TMR ratio increased up to 300 °C but the TMR ratio of a specular MTJ increased up to 400 °C. The highest TMR ratios of two samples after annealing at each optimal temperature were 21.6% (conventional MTJ) and 22.7% (specular MTJ), respectively, This improved thermal property of the specular MTJ is due to the NOL, which could act as a diffusion barrier for Mn. The biasvoltage dependence of both samples was vastly improved after annealing at each optimal temperature.