Low spin-polarization in the heavy metal\ferromagnet structures detected through the domain wall motion by synchronized magnetic field and current

TL;DR

This study investigates the low efficiency of domain wall motion in Ta/CoFeB/MgO nanowires, revealing an unexpectedly low spin polarization rate of 0.26, likely due to spin relaxation effects in the Ta layer.

Contribution

The paper provides experimental evidence of low spin polarization in heavy metal/ferromagnet structures, highlighting its impact on domain wall motion efficiency.

Findings

Low spin polarization rate of 0.26 detected

Spin relaxation in Ta layer may cause low polarization

Implications for racetrack memory technology

Abstract

CoFeB is a very soft material, in which Domain Wall (DW) can be moved easily under a weak magnetic field. However, it is very difficult to move DWs in Ta\CoFeB\MgO nanowires with interfacial perpendicular magnetic anisotropy through a spin-polarized current, and this limits the perspectives of racetrack memory driven by the current-in-plane mechanism. To investigate this phenomenon, we performed experiments of DW velocity measurement by applying a magnetic field and a current simultaneously. Working in the precessional regime, we have been able to see a very important effect of the spin-polarized current, which allows evaluating the polarization rate of the charge carriers. An unexpected quite low spin polarization rate down to 0.26 have been obtained, which can explain the low efficiency of DW motion induced by the spin-polarized current. Possible reasons for this low rate are analyzed, such as the spin relaxation in the Ta layer.