Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal

TL;DR

This paper investigates how thermal fluctuations influence the magnetic field dependence of spin transfer induced magnetization reversal in nanoscale CPP magnetic sensors, revealing discrepancies with theory that are resolved by considering thermal effects.

Contribution

It introduces a fabrication process for nanoscale CPP magnetic sensors and demonstrates the importance of thermal fluctuations in explaining magnetization reversal behavior.

Findings

Critical currents vary significantly with small magnetic field changes.

Thermal fluctuations explain discrepancies between experiments and theory.

Numerical simulations align with experimental data when thermal effects are included.

Abstract

We have developed a self-aligned, high-yield process to fabricate CPP (current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions. A pinned synthetic antiferromagnet (SAF) 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 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.