Evolution of switching fields caused by reorientation of GdFeCo/Ir/GdFeCo synthetic ferrimagnet in magnetic field

Abstract

Anomalous Hall effect (AHE) in GdFeCo/Ir/GdFeCo multilayered structures attracts great interest because all optical switching, spin-torque, and other effects promise effective application for ultrafast memory element creation. Since AHE is controlled by GdFeCo magnetization, domain dynamics has importance for practical applications. In our work, magnetization reversal in perpendicular GdFeCo/Ir/GdFeCo synthetic ferrimagnets is characterized by AHE measurements. The AHE hysteresis loop obtained with the field applied perpendicular to the sample plane is composed of three sub-loops, and two of them are symmetrically biased with respect to the third one. Switching magnetic fields for two of the three transitions are found to be dependent on magnetic history. In particular, exposure of the sample in the in-plane field leads to reduction of the out-of-plane switching fields in side sub-loops. A multiple series of perpendicular hysteresis loops recorded after exposure under high in-plane field reveals gradual (within 30 min) relaxation of the out-of-plane switching fields to their initial values observed in a non-magnetized sample. Domain wall mobility, limiting switching of the bilayer devices, is complicated due to the coupling between partial domains in each single layer. Unusual dynamics of double domain walls results in unexpected new phenomena affecting electrical processes in bilayer structures.