Magnetization Reversal Dynamics of a Heusler Alloy Exchange-Coupled with a Synthetic Antiferromagnet

Abstract

This work shows the dynamics of the process of the magnetization reversal of a thin film of the Heusler alloy Co₂FeSi in the stack of a multilayer structure with a magnetic tunneling junction that has a tunnel magnetoresistance (TMR) of 149%. Using the method of a magneto-optical indicator film, the process of magnetization reversal of this layer is visualized. Anisotropy of the magnetization reversal of the Co₂FeSi layer under the action of in-plane magnetic fields is found. The behavior of the magnetization reversal under the action of fields applied perpendicular to the easy axis of the induced anisotropy indicates smooth, coherent rotation of the magnetic moment from the easy axis towards the applied field. As the external field is directed along the easy axis, a complex domain structure appears and its asymmetric nucleation and movement are observed. The domains propagate and move depending on the direction of the field, when the external field is directed along the easy axis. For example, when the field is antiparallel to the direction of the easy axis of the free layer, domains nucleate at the edges of the film and propagate inward. The magnetization of the free layer becomes antiparallel to the magnetization of the upper layer of the synthetic antiferromagnetic film (IrMn/CoFe/Ru/CoFeB). When the field is switched to the opposite direction, domains originate inside the film and propagate to its edges to transfer the magnetization of the free layer to a parallel position to the reference layer. These results are important for improving the quality of Heusler-alloy-based magnetic tunneling junction devices.