Effects of mobile oxygen ions in top-gated synthetic antiferromagnet structure

Abstract

In this work, we study the effects of mobile oxygen ions in a synthetic antiferromagnet structure gated by a sputtered SiO2 dielectric layer for memory and logic applications. Our devices utilize electrochemical reactions between dielectric reactive species and magnetic elements to create irreversible changes in magnetization. We analyzed the dependence of ion velocity on the gate dielectric properties such as the lattice parameter, oxygen migration energy barrier, and electric field (E-field). Hall bar devices were patterned and tested to determine the interlayer exchange coupling between the CoFeB and [Co/Pd]n layers. The anomalous Hall effect (AHE) of the CoFeB layer at different gate voltages (Vg) was measured to determine the Vg dependence. A sharp change in the behavior of the CoFeB layer with respect to negative Vg results in a non-reciprocal decrease in the coercivity and magnetization and an increase in exchange bias. The observed change in exchange bias field and magnetization allows us to measure the change in the effective thickness of the CoFeB layer. This led us to conclude that the source of such behavior is the negatively charged mobile oxygen ions from the SiO2 gate.