Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO

TL;DR

This study investigates how the current-induced effective magnetic field in Ta|CoFeB|MgO heterostructures depends on layer thickness, revealing significant variations and sign changes with nanometer-scale adjustments, crucial for magnetic device control.

Contribution

It provides the first quantitative vector measurements of the effective field's dependence on layer thickness, highlighting the competing effects influencing magnetization manipulation.

Findings

Effective field varies significantly with Ta and CoFeB thickness.

A 1 nm change in Ta thickness can alter the effective field by nearly two orders of magnitude.

The sign of the effective field reverses with decreasing Ta thickness.

Abstract

The role of current induced effective magnetic field in ultrathin magnetic heterostructures is increasingly gaining interest since it can provide efficient ways of manipulating magnetization electrically. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we show vector measurements of the current induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field shows significant dependence on the Ta and CoFeB layers' thickness. In particular, 1 nm thickness variation of the Ta layer can result in nearly two orders of magnitude difference in the effective field. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects that contribute to the effective field. The relative size of the effective field vector components, directed transverse and parallel to the current flow, varies as the Ta thickness is changed. Our results illustrate the profound characteristics of just a few atomic layer thick metals and their influence on magnetization dynamics.