Investigation of field-free switching in Co/Ta/CoGd ferrimagnetic trilayer

Abstract

Field-free switching, in which the magnetization of magnetic structures is manipulated under the absence of an external magnetic field, is essential for the development of miniaturized spin-orbit torque (SOT) based memory devices. There have been previous studies on successful field-free switching using ferromagnet (FM) / heavy metal (HM) / ferromagnet trilayer structures with in-plane and out-of-plane anisotropy of each FM layer. Substituting the ferromagnetic source layer with a ferrimagnetic layer can lead to interesting results, such as enhancement in switching efficiency. In this study, trilayer structures of Co / Ta / CoGd trilayer structures are investigated. CoGd is the ferrimagnet layer, and is varied in composition for control of magnetic properties. Experimental results show successful field-free switching in the trilayer structures, and the spin current source is found as the CoGd layer. Also, a significant decrease of switching current density along with switching direction inversion is observed near compensation of the CoGd layer. The spin current generation from the CoGd layer and switching signal inversion cannot be explained currently, and further investigation is required.