Thermally assisted spin transfer torque (STT) switching of hybrid memory stacks with a low Curie temperature (TC) CoPd/Pd multilayers (MLs) and high TC Co/Pd MLs were investigated. Current-perpendicular-to-the-plane giant-magneto-resistance (CPP-GMR) structures with a stack of [Co/Pt]6/Cu/[Co/Pd]M/[CoPd/Pd]N (M + N = 3) were fabricated. The intrinsic critical current density (Jc0) and thermal stability factor Δ of the hybrid memory layer were evaluated from the STT-switching of the CPP-GMR. Jc0 and Δ were found to be almost independent of the pillar diameter, and the effective reversal size contributing to Δ was found to be much smaller than the physical pillar diameter. At room temperature, slight decreases of Jc0 and Δ were confirmed with increasing the thickness ratio of the low TC MLs (N) in the hybrid memory layer. At high temperature of ~150 °C, Jc0 and Δ were found to significantly reduce, suggesting the thermally assisted STT switching by using the low TC/high TC hybrid memory layer.
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