Electrical Control Of Ferromagnetism In Pt/Co(Ni)heterostructures

In recent years,the applications of electronic and information technology have become an important part of our daily lives,people are increasingly desired for devices with high storage capacity,high response speed and long battery life.In the field on information storage technology,the spintronic devices based on metallic multilayers structures are considered to be a promising development aspect.The metallic multilayers with perpendicular magnetic anisotropy?PMA?have attracted the researchers interest due to their high thermostability,low energy consumption and capability for small-dimension devices.This dissertation proposes the main idea of modulating the ferromagnetism and spin-orbit torque in PMA Pt/Co and Pt/Co/Ni heterostructures with the help of ionic liquid gating,and investigating the mechanism of electrical control effects.Firstly,we deposited Pt/Co/Ni/HfO₂ multilayer structure with PMA and fabricated it into Hall devices with ionic liquid gate.We have tuned the saturation magnetization and Curie temperature in a large scale within small gate voltages.By analyzing the valence state of interfacial atoms,we revealed at the interface between metal and HfO₂ which has low O₂-mobility,the interfacial oxidation-reduction reaction contributes to the electrical control of ferromagnetism,which we called electrochemical mechanism.Using the first-principles calculations we clarified that the change of 3d electron density under electrostatic effect is the origin of the change of Curie temperature.We demonstrated that the electrochemistry mechanism and electrostatic interaction both play crucial roles in the electrical control effect,which can help the researchers acquire better understanding of electrical control of magnetism in metal/oxide systems.Secondly,we achieved the current-induced magnetization switching in Hall devices based on PMA Ta/Pt/Co/HfO₂ thin films,and discovered that the critical switching current is sensitive to the sample temperature and the orientation of external magnetic field.The critical switching current could be tuned by a factor of more than two with the help of ionic liquid,which is a non-volatile effect.We excluded the contribution of the variation of ferromagnetism for the change of critical switching current and verified that the electric field effect on effective spin Hall angle of Pt/Co system and the corresponding current-induced effective field is the dominant reason for the change of critical switching current.Our findings may advance the process towards the low-energy-consumption and compatible memory and logic devices based on spin-orbit effects.