| Exchange bias effect is an important basis of information storage technology.As the most basic structural unit of magnetic memory devices,ferromagnetic(FM)/ antiferromagnetic(AFM)exchange bias system has been widely used in a variety of magnetoelectronic devices,such as computer readout heads and various magnetic sensors.However,with the pursuit of high-density,low-power,high-speed,nonvolatile and other technical indicators of information storage technology in recent years,the pure FM / AFM exchange bias system can not meet the development requirements.Through the way of magnetoelectric coupling,the magnetic moment or magnetic multi-domain state of the exchange bias system can be changed by using the action of electric field or current,which will optimize the magnetic storage design.There are still great challenges to fully realize the regulation of electronically controlled exchange bias under the condition of room temperature and zero magnetic field.Most of the research work is limited by an external magnetic field and high driving current density.In this paper,we systematically studied the influencing factors of the exchange bias of NiFe/NiO film.The electrical-controlled-magnetism is realized by applying longitudinal electric field or transverse current pulse to induce the changes of magnetic moment or magnetic multi-domain state in magnetic materials.The results are as follows:1.The effects of sputtering power amount,antiferromagnetic layer thickness and ferromagnetic layer thickness on the microstructure and magnetic properties of NiFe/NiO exchange bias films were systematically studied.When the sputtering power of NiO film is110 W,NiO film shows good crystallinity and the exchange bias field is the largest.The exchange bias effect of NiFe/NiO bilayers decreases first and then increases with the increase of NiO film thickness.and it decreases gradually as the NiFe thickness increases.2.Annealing treatment will change the microstructure,roughness and morphology of the interface of FM AFM exchange bias films,which is very important to the magnetic properties such as exchange bias.Non-collinear magnetic anisotropy was induced by annealing NiFe(15nm)/NiO(130nm)bilayers in air.It is mainly caused by the roughness of FM-AFM exchange bias interface and the change of spin structure of magnetic domain after annealing.The NiFe(15nm)/NiO(110nm)structure samples after annealing in air significantly increases the exchange bias effect and coercivity.The main chemical reactions in the film change the crystal structure and phase composition.It is proved that the non-collinear magnetic anisotropy is related to the thickness of antiferromagnetic layer,crystal structure and phase composition.3.Based on the resistance variation characteristics of NiO thin films,the nonvolatile regulation of magnetic properties in the NiFe/NiO multilayer thin film is regulated by applying an electric field longitudinally at room temperature.By applying electric field to the NiFe/NiO multilayer film in the longitudinal direction,the resistance of the system is induced to change nonlinearly into a low resistance state.The mechanism of resistance change is electronic resistance change.In the low resistance state,the exchange bias field is reduced,which is mainly related to the inversion and the movement of the interface magnetic moment after the electron is captured by the defect oxygen vacancy.When the forward and reverse magnetic fields assist the electric field to act on the sample,the reverse magnetic field promotes the reverse reversal of magnetic moment and magnetic domain under the electric field,while the forward magnetic field inhibited the reverse.4.The magnetic properties of NiFe/NiO bilayer films subjected to parallel surface(transverse)pulse current under the condition of zero magnetic field were studied.The magnetic moment after an electric pulse effect happened to a 180 ° nonvolatile reversal.In this process,the single domain state of ferromagnetic layer is separated into multi-domain states with magnetization parallel or antiparallel to each other,forming positive and negative alternating stripe domains.We have realized the nonvolatile reversal of magnetic moment through the action of low current density without the assistance of external magnetic field.The effects of pulse current direction,ferromagnetic layer thickness,antiferromagnetic layer thickness,electrode materials and verification temperature under the condition of liquid nitrogen on this phenomenon are verified.It is found that they will not affect the occurrence of double displacement hysteresis loop phenomenon.At the same time,the magnetic properties of the exchange-bias film under multiple transverse electric pulses have multiple repeatability and reversible recovery under reverse magnetic field.This provides a new method for the further study of the exchange bias mechanism and the realization of nonvolatile magnetic moment reversal under zero field. |
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