Thermal effects on the magnetic-field dependence of spin-transfer-induced magnetization reversal

We have developed a self-aligned, high-yield process to fabricate current-perpendicular-to-plane giant magnetoresistance (GMR) spin-valve sensors of sub-100-nm dimensions. A pinned synthetic antiferromagnet is used as the reference layer which minimizes dipole coupling to the free layer and field-induced rotation of the reference layer. We find that the critical currents for spin-transfer-induced magnetization reversal of the free layer vary dramatically with relatively small changes in the in-plane magnetic field, in contrast to theoretical predictions based on stability analysis of the Gilbert equations of magnetization dynamics, including Slonczewski-type spin-torque terms. The discrepancy is believed due to thermal fluctuations over the time scale of the measurements. Once thermal fluctuations are taken into account, we find good quantitative agreement between our experimental results and numerical simulations.