Electrical And Optical Detection Of Spin Transfer Torque Based On Vertical Magnetic Anisotropy

High density microelectronic devices are faced with high heat loss per unit area,which seriously restricts the development of the next generation of microelectronic devices.Spintronics is the deep development and utilization of electronic devices by using the spin properties of the electron itself.In terms of storage applications,spintronics have the characteristics of low power consumption,high density storage and non-volatile.A series of major discoveries,such as tunneling magnetoresistance effect,spin Hall effect,spin orbit coupling,spin orbit torque,spin transfer torque,etc.They promote the development of spintronics.At present,the front of spintronics is to study the mechanism and efficiency of spin transfer torque,that is,in spin electronic devices,using spin current to write magnetic storage information and other functions.In terms of the mechanism and efficiency of the spin transfer torque,it is necessary to study the generation,transmission and detection of the spin current.Using spin Hall effect,optical spin voltage effect and spin Seebeck effect to cause the accumulation and transmission of non-equilibrium spin,spin current is produced.The transmission of spin current mainly involves spin diffusion process.At present,the most commonly used method to detect spin current is to transform the spin current into the charge current,and the size of the charge current reflects the size of the spin current.Spin current is used to reverse the magnetic moment and write information.In this process,spin current plays the role of spin transfer torque.In order to improve the efficiency of charge current induced spin transfer torque(spin transfer torque induced effective field/current density of heavy metal),many people prefer to use materials with strong spin orbit coupling to convert charge current into more spin current.To further enhance the spin transfer torque efficiency,new method is required in device designing,which could be done by optimizing the spin diffusion process besides by improving the charge-spin current conversion.In this work,using the harmonic Hall measurement method,we studied the STT efficiency in platinum(Pt)/FM structures as a function of the Pt thickness.We found that the STT efficiency strongly depends on the Pt thickness and reaches a maximum value of 4.259 mT/(A/cm2)for the 1.8-nm thickness Pt sample.This result indicates that competition between spin Hall effect(SHE)and Rashba effect as well as spin diffusion process across the Pt layer determines the Pt thickness for the maximum STT efficiency.At the same time,the magneto-optical Kerr effect of the sample is measured,then analyze the result and compare this result to that using harmonic Hall measurement method.We demonstrated the role played by the spin diffusion besides the spin current generation mechanisms in improvement of the STT efficiency,which is helpful in designing STT-based devices.