Spin-orbit Torque Effect In Co Films With Perpendicular Magnetic Anisotropy

With the development of science and technology,people require the stronger performance of electronic devices,which promotes the rapid development of spintronics devices in recent years.With the development and application of giant magnetoresistance(GMR)and tunneling magnetoresistance(TMR)devices.new devices with higher energy efficiency,lower Joule-heating and simpler structure are required.And spin-orbit torque(SOT)devices are just a new generation of spintronics devices which can meet these requirements.SOT devices use electric current to replace magnetic field as a novel method to manipulate the magnetic moment of thin films and the resistive state of devices.Compared with the magnetic field,the electric current manipulation eliminates the process of using electromagnet to convert the current into magnetic field.And the overall structure of the device is simpler,with higher energy efficiency and smaller thermal effect.Thus,SOT devices have a very wide prospect of application in the electronics industry.In this paper,the Co films with perpendicular magnetic anisotropy is used as the core to prepare SOT devices.And the enhancement of SOT by inserting metal films are studied.In addition,the properties of the SOT devices are tested,and the source of spin current in the devices is studied.The main results are as follows:(1)Ta/Pt/Co/Pt mutilayers were fabricated to be SOT devices on SiO2 substrates.And Ta/Pt/Co/Ru/Pt SOT devices were fabricated with metal Ru as the insertion layer to study the manipulation of SOT.It was found that the critical switching current densities of the SOT devices with 0.6 nm and 1.0 nm Co films decreased by 11.2%and 45.1%,respectively,after the insertion of Ru films.After the harmonic hall-voltage measurements,we calculated their SOT effective fields.The results show that using Ru as insertion layer can significantly enhance the SOT effective field.We attribute this enhancement to the unique ability of the Ru film to scatter the majority spins at the interface stronger than the minority spins.(2)SOT devices with Ta/Pt/Co/Ru/AlOx structure were fabricated by inserting metal Ru films into Ta/Pt/Co/AlOx structure.In contrast,the temperature dependence of the SOT effective fields of the devices before and after the insertion of the Ru layer was measured.And the variation trend of the spin hall magnetoresistance with temperature was also compared.It is found that the effective SOT fields of the devices remain decreases with the decrease of temperature before and after inserting Ru layer.While the trend of SMR has changed.Without the Ru layer,the SMR of the device increases continuously with the decrease of temperature.After the Ru layer is inserted,the SMR increases first and then decreases as the temperature decreases.We attribute the difference of temperature dependence between SOT and SMR to the influence of the interface-generated spin at the Co/Ru interface.(3)SOT devices were prepared by Ta/Pt/Co/Tb/Pt and Ta/Pt/Co/Tb/AlOx multilayers and compared with the samples without rare earth metal Tb layers.It is found that the insertion of metal Tb films can effectively reduce the critical switching current of SOT devices and increase the SOT effective fields.The temperature dependence of SOT effective fields and SMR were measured.It was found that the SOT effective fields of the device with insertion Tb films increased rapidly with the decrease of temperature,and then decreased when the temperature was lower than 100 K.We attribute this change to the partial antiferromagnetically coupled of Co/Tb films.The SOT effective fields of the devices increase rapidly as the temperature decreases to the temperature compensation point.And when the temperature is lower than the temperature compensation point,the effective SOT field decreases with the decrease of temperature.