Thermally assisted switching of exchange coupled bi-layer with different ordering temperature

Thermally assisted magnetization reversal is studied for a novel bi-layer system of in-plane magnetized TbFe/CoFe with different ordering temperature in each layer, aiming at the application to MRAM memory operation. Temperature sensitive magnetisation reversal is performed with a microstructured pseudo spin valve cell with TbFe/CoFe as a hard layer. Numerical simulation for thermal switching is also carried out and compared with experimental results. From the in-plane M-H hysteresis curve, the temperature dependence of coercive field H_c for an as-grown TbFe/CoFe film is evaluated. The in-plane magnetization of the bi-layer system suggests that the geometrical in-plane anisotropy of CoFe exceeds perpendicular anisotropy of TbFe. Thermal reduction of the coercive field is also observed in the MR hysteresis profiles for the patterned pseudo spin valve sample. An enhanced coercive field is observed in the cell compared to that observed in as-grown film. This is attributed to the lateral shape anisotropy in the patterned structure.