Investigation On The Exchange Bias Of Ferromagnetic/Antiferromagnetic Thin Films

As the key of information storage,the development of magnetic storage technology has been paid much attention in the world.Due to its unique physical properties,the exchange bias effect can play an important role in the evolution of novel high-density magnetic storage technology,it has always been a research hotspot.In this paper,a series of Co/IrMn bilayer films were prepared by magnetron sputtering on Si and LiNbO₃ substrates respectively.The effects of the thickness of ferromagnetic and antiferromagnetic,temperature and Surface Acoustic Wave(SAW)on the exchange bias effect were studied in detail by means of Vibrating Sample Magnetometer(VSM)and Magneto-optic Kerr Microscope(MOKM).The main results are as follows:(1)Si/Pt/Co/IrMn samples with perpendicular exchange bias effect were prepared by introducing Pt/Co material.Firstly,the influence of antiferromagnetic layer thickness on exchange bias field(H_EB),coercivity(H_C)and domain structure was investigated by VSM and MOKM.When the thickness of IrMn is 5.6 nm,an unusual double-shifted mangnetization curves phenomenon is observed.With the further increase of IrMn thickness,the unusual double-shifted hysteresis loop still exists.The phenomenon is mainly due to the fact that the density of net spins pinned to the Co layer is different in the IrMn layer.Then,the Co layer thickness is systematically changed to ensure that the sample has good perpendicular anisotropy while the obvious exchange bias effect can be observed.In addition,we used the heating system of VSM to researched the relationship between the H_EB and the temperature.When the temperature rised to 390 K,the exchange bias effect disappearsed completely.The reason may be that the temperature has risen to the bloch temperature of IrMn,which leads to the IrMn into paramagnetic state and no longer has the pinning effect on Co layer.(2)We used the magnetic field annealing to induce the exchange bias effect of Si/Co/IrMn thin film.The influence of annealing temperature on magnetic properties of samples was investigated by VSM.The measurement result of VSM show that with the increase of temperature,the H_EB increases firstly and then it gradually stabilizes.This may be caused by the size change of antiferromagnetic grains.Then,by changing substrate,it is found that the H_EB of the sample on Si<111>substrate is larger than that on LiNbO₃ substrate.(3)We fabricated SAW devices on LiNbO₃ substrate by magnetron sputtering and lithography technology.The effect of SAW on H_EB and H_C of thin films were studied by MOKM.Compared with the case without SAW,the H_EB and H_C of the samples decrease because the dynamic strain field of SAW periodically regulates the ferromagnetic and antiferromagnetic anisotropic potential barriers.Besides,the value of H_C is linearly related to the size of driving power.