Magnetization Switching Of Ferrimagnetic CoTb

Over the past few decades,a variety of physical effects related to the spin properties of electrons have been proposed.Various functional devices have been prepared based on these effects,which have accelerated the development of Spintronics.High-quality Pt/Co/AlOx multilayer films were prepared in 2011,and the magnetization switching driven by spin-orbit torque(SOT)was realized,which led to an upsurge in the study of SOT-based magnetic random access memory(SOT-MRAM).Spintronic devices based on the SOT effect have the advantages of non-volatility,high computing speed,low power consumption,and good compatibility with traditional semiconductor processes,making the SOT effect useful in data storage,logic operations,high-frequency magnetic devices,and neuromorphic computing.In particular,synthetic antiferromagnetic(ferrimagnetic)materials composed of rare earth/transition metal(RE/TM)alloys or RE/TM heterostructures are ideal carriers for constructing functional devices based on spin-orbit torque.This material system has the following advantages:1.The synthetic antiferromagnetic structure has low stray field,which is beneficial for the integration of the device,meanwhile,the internally ordered ferromagnetic characteristics are retained,which is convenient for signal detection by electrical methods.2.Elements such as Gd and Tb,have large atomic magnetic moments.Their alloys usually have strong perpendicular magnetic anisotropy in a wide range of compositions with a Curie temperature near or above room temperature.These properties not only enable the effective control the material properties utilizing composition,temperature,stress,etc.,but also are crucial to the development of ultrahigh density perpendicular magnetic recording devices.3.The RE/TM heterostructure has rich interfacial effects such as magnetoresistance effect,magnetic proximity effect,spin pumping effect,etc.,which is promising for the development of spin-complementary metal compound semiconductor devices,magnetic random access memory,magnetic logic devices,and other functional spintronic devices.On one hand,we have obtained the magnetization compensation point of ferrimagnetic CoTb alloy at room temperature.By using co-sputtering of Co target and Tb target,we prepared a series of CoxTb100-x films.Based on the magnetic hysteresis loops and anomalous Hall measurements,it is observed that the magnetization of the Co71Tb29 sample is compensated at room temperature.On the other hand,we have studied the magnetization switching in ferrimagnetic CoTb alloys at room temperature.First,we investigated spin-orbit torque induced magnetization switching in Ru(2)/Pt(5)/Co65Tb35(10)/Ru(3)and Ru(2)/Pt(5)/Co75Tb25(8)/Ru(3)(thickness in nanometer)multilayers.In the above multilayer films,the macroscopic magnetic properties of Co65Tb35 and Co75Tb25 are dominated by Tb and Co elements,respectively.Measurements of current-induced magnetization switching show that the magnetization switching greater than 60%can be obtained under a small auxiliary magnetic field below 100 Oe.The magnetization switching ratio of the Co65Tb35 sample can reach up to 75%,and its critical switching current density(Jc)is 1.25×107A/cm2.Secondly,ferrimagnetic CoTb has been introduced into the synthetic antiferromagnet,and the SOT-induced magnetization switching and RKKY interlayer exchange coupling in the synthetic antiferromagnet have studied.We prepared the following four types of samples:Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(1.3)/Co75Tb25(8)/Ru(3)(FMCo75Tb25),Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(0.8)/Co65Tb35(10)/Ru(3)(FM-Co65Tb35),Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(0.8)/Co75Tb25(8)/Ru(3)(AFM-Co75Tb25)and Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(1.3)/Co65Tb35(10)/Ru(3)(AFM-Co65Tb35).Both the FMCo75Tb25 and the FM-Co6sTb35 exhibit the form of ferromagnetic coupling macroscopically,and their magnetization switching ratios are up to 38%and 68.8%and their critical current densities are 1.80×107 A/cm2 and 1.53×107 A/cm2,respectively.The AFM-Co75Tb25 and the AFM-Co65Tb35 exhibit the form of antiferromagnetic coupling macroscopically,and their magnetization switching ratios are up to 82%and 75%and their critical current densities are 1.69× 107 A/cm2 and 1.64× 107 A/cm2,respectively.When an in-plane auxiliary field of+3500 Oe is applied,the current-induced SOT effective field in the AFM-Co65Tb35 varies linearly with the current.Finally,the variation of the interlayer coupling with the thickness of Ru sublayer in the Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(X)/Co75Tb25(8)/Ru(3)(RuX-Co75Tb25)and the Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(X)/Co65Tb35(10)/Ru(3)(RuX-Co65Tb35)is investigated.The maximum exchange coupling field is 3876 Oe in the RuX-Co75Tb25 sample when the Ru layer thickness is 0.7 nm,and it is 969 Oe in the RuX-Co65Tb35 sample when the Ru layer thickness is 1.3 nm.By controlling the thickness and composition of the upper and lower magnetic sublayers in the synthetic antiferromagnet,the anomalous Hall signal is enhanced in Ru(2)/Pt(5)/Co(0.4)/Pt(0.3)/Co(0.4)/Ru(1.3)/Co65Tb35(10)/Ru(3)while the total magnetic moments of the upper and lower magnetic layers are compensated.It provides an ideal platform for the research of high-density magnetic storage and spin logic devices based on synthetic antiferromagnetic structures.