Investigation Of Perpendicular Exchange Bias Effect And Its Manipulation In Pt/Co/IrMn Thin Films

The development of the information era has put forward placed higher requirements for the technical level of data storage.Magnetic random memory（MRAM）has become a popular research field in data storage due to its advantages of high storage speed,high density,and high stability.The successful application of the exchange bias（EB）effect at the ferromagnetic（FM）/antiferromagnetic（AFM）interface in memory cells has greatly promoted the development of MRAM.The thin film with perpendicular magnetic anisotropy（PMA）overcomes the superparamagnetic limit brought about by device miniaturization to a certain extent.Therefore,the EB effect with PMA has become a hot topic of research in recent years.However,there is a lack of in-depth research on the intrinsic physical mechanisms of the EB phenomenon,the EB phenomenon in FM/AFM/FM trilayers,and how to better manipulate the EB.Therefore,this work investigated the specific reasons for bidirectional exchange bias phenomena in Pt/Co/IrMn thin films.Subsequently,the effect of the magnetic moment direction of the upper Co layer on the exchange bias field(H_EB)and coercivity（H_C）at the lower Co/IrMn interface in Co/IrMn/Co trilayers was investigated.Finally,the modulation of H_EB by SAW is studied in surface acoustic wave（SAW）devices.The main findings and results of this thesis are as follows:1.Co/IrMn perpendicular EB bilayer films with different IrMn layer thicknesses(t _IrMn)were prepared on Si（111）substrates.The experimental results show that with the increase of t _IrMn,HEB first increases and then stabilizes around 1100 Oe,while the H_C first increases and then decreases and finally stabilizes around 430 Oe.Interestingly,the hysteresis loops show a bidirectional exchange bias phenomenon when t _IrMn is greater than 8 nm,by analyzing the magnetic domains in the remanent state and Co/IrMn interface coupling of the sample shows that this phenomenon is due to the spontaneous domain division at both the FM layer and the AFM interface.2.Co/IrMn/Co perpendicular EB trilayers with different structures were prepared on Si（111）substrates,and the effects of the presence or absence of the upper Co layer and its magnetic moment direction on the H_EB and H_C at the lower Co/IrMn interface were investigated.The experimental results show that when the magnetic moment direction of the upper Co layer is in-plane,it has almost no effect on the H_EB and H_Cgenerated at the lower Co/IrMn interface.However,when the magnetic moment of the upper Co layer also has a PMA（the magnetic moments of the two FM layers are collinear）,its existence causes a significant reduction in H_EB and H_C.The results of the variable temperature hysteresis loops show that the H_EB,H_C,and blocking temperature are smaller when the magnetic moments of the two Co layers are co-linear than in the non-co-linear case.3.The effect of continuous and pulsed SAW on the H_EB in Co/IrMn films was investigated in SAW devices fabricated on LiNbO₃ single crystal substrates.The results show that the H_EB of the sample decreases as the continuous SAW input power（within a certain range）increases,while the H_EB decreases and then stabilizes under pulsed SAW,and the former decreases to a greater extent than the latter.Combining the changes in the Hall resistance of the sample in both cases,it can be deduced that the effect of continuous SAW on H_EB is a comprehensive effect of dynamic strain field and thermal effects.