Study On The Spin Orbit Torque Effect In Pt/Co-Tb Structures

Current-induced spin–orbit torque(SOT)in magnetic heterostructures has attracted widespread attention for its rich physical connotation and potential application in information storage and logic devices.Since the discovery of this effect,the core research topics in this field have mainly included exploring the source of SOT in NM/FM heterostructures and the dynamic behavior of magnetization induced by SOT,such as the current induced magnetic moment precession,domain wall(DW)motion,the physical mechanism and microscopic process of magnetization switching,etc.In terms of application,antiferromagnetic metal(AFM)has terahertz dynamics and the immunity against external magnetic perturbation.In comparison with ferromagnetic(FM)materials,AFM materials can be used in next-generation of information storage media due to its higher reading and writing speed and storage density.The main difficulty associated with the usage of AFM as a memory cell in spintronic devices is the lack of a mechanism for realizing efficient reading and writing,but the ferrimagnetic transition metal(TM)-rare earth(RE)alloys can offer a solution for this difficulty.However,the physical mechanism of the SOT effect in the non-magnetic/TM-RE structure is still inadequate,especially the current-induced magnetization switching microscopic process and its correlation with spin orbit torque and Dzyaloshinskii-Moriya interaction(DMI),so in this article,we mainly studied the SOT effect and the current-driven magnetization switching phenomenon in the heavy metal(HM)/transition metal-rare earth alloy(TM-RE)structures.The main contents are:1)We fabricated series of sample with different component,the sample structure is Ta/Pt/Co-Tb/Ta.And we determined the SOT effective field and DMI field of samples with different composition by utilizing the current-induced loop shift method,we also measured the SOT efficiency in these samples by using the second harmonic scanning field method.The experimental results show that the current-induced SOT effective field conforms to the 1/M_s rule within the composition range we measured.Then we obtained the effective spin Hall angle is about 0.07 for the samples with different Co-Tb compositions,which is basically consistent with the spin Hall angle measured in the Pt/FM structure.It is confirmed that the effective field we measured is mainly derived from the spin current generated in Pt.Above,we also found that in the samples with Co-dominated,the H_DMI also showed a downward trend with the increase of Co content.2)To investigate the current induced magnetization switching phenomenon in Ta/Pt/Co-Tb/Ta(Si N_x)series samples by means of electrical measurement methods and microscope imaging of the magneto-optic Kerr effect(MOKE).In Ta/Pt/Co-Tb/Ta samples,as the Co content increases,the current-driven magnetization switching transitions from“steep switch”to“continuous gradient”.Then we used the MOKE microscope to observe the change of the magnetization state during the current-driven process.The research results of the MOKE microscope show that the in-plane field will influence the growth of the magnetization nucleation.In addition,we found that the growth modes of the magnetization nucleus are different in the samples with different Co content.The sample with lower Co content is a general model of domain wall motion during the switching process.However,the sample with higher Co content showed continuous nucleation process due to the domain wall pinning and magnetic anisotropy.Finally,we fabricated a series of samples Ta/Pt/Co-Tb/Si N_x with component compensation points.The current-induced magnetization switching curve and the MOKE microscope measurement results show that the polarity of the current-driven magnetization switching has not changed before and after the compensation point.This phenomenon can be explained by the change in the compensation state caused by the Joule heating generated by the current.