Determination of the Spin-Hall-Effect-Induced and the Wedged-Structure-Induced Spin Torque Efficiencies in Heterostructures with Perpendicular Magnetic Anisotropy

TL;DR

This paper measures and compares spin torque efficiencies induced by the spin Hall effect and wedged-structure asymmetry in heterostructures with perpendicular magnetic anisotropy, revealing new ways to control spin-orbit torque switching.

Contribution

It introduces a measurement technique for spin Hall effect contribution and uncovers an additional torque component from asymmetric ferromagnetic layer deposition.

Findings

Quantified SHE-induced effective field in Pt and Ta heterostructures.

Discovered an extra effective field due to asymmetric ferromagnetic layer deposition.

Linked asymmetry to domain expansion control during magnetization switching.

Abstract

We report that by measuring current-induced hysteresis loop shift versus in-plane bias magnetic field, the spin Hall effect (SHE) contribution of the current-induced effective field per current density, $\chi_{SHE}$, can be estimated for Pt and Ta-based magnetic heterostructures with perpendicular magnetic anisotropy (PMA). We apply this technique to a Pt-based sample with its ferromagnetic (FM) layer being wedged-deposited and discover an extra effective field contribution, $\chi_{Wedged}$, due to the asymmetric nature of the deposited FM layer. We confirm the correlation between $\chi_{Wedged}$ and the asymmetric depinning process in FM layer during magnetization switching by magneto-optical Kerr (MOKE) microscopy. These results indicate the possibility of engineering deterministic spin-orbit torque (SOT) switching by controlling the symmetry of domain expansion through the materials growth process.