Investigation On The Magnetic Anisotropy And Magnetic Domain Structure Of Co/IrMn Exchange-bias System

With the rapid development of the information industry,a large amount of information needs to be saved and managed,which puts forward higher requirements for information storage technology.The new generation of magnetic memory devices stands out from many memories with its advantages of high storage density,fast access speed,low power consumption and miniaturization.Researchers have found that the exchange bias effect of ferromagnetic(FM)/antiferromagnetic(AFM)films plays an important role in the new generation of magnetic memory devices,but many problems related to FM/AFM interface interaction are still lacking in-depth study.For example,there are the non-collinear behavior between uniaxial anisotropy and unidirectional anisotropy and asymmetric magnetization reversal phenomenon in the exchange bias system.The existence of these problems will reduce the access speed of memory,storage stability,etc.Therefore,studying these problems has important significance for understanding the mechanism of the exchange bias effect and constructing an efficient and stable magnetic memory device.In addition,with the rapid development of spintronics based on magnetic materials,controlling the magnetic domains of the magnetic ultra-thin films is also extremely important for the basic research of domain wall dynamics and its application in low-power devices in the future.Based on the above problems,we investigated the non-collinear anisotropy,exchange bias field and magnetic domain structure of the Co/IrMn exchange bias system by using vibration sample magnetometer,electron spin resonance spectrum,magneto-optic Kerr microscope.The results are as follows:(1)In the Co/IrMn films with in-plane exchange bias,the non-collinear angle between uniaxial anisotropy and unidirectional anisotropy of the film is controlled by changing the thickness of the Co layer.The experimental results show that the exchange bias field and the non-collinear angle decrease with the thickness of the Co layer increases.When the non-collinear angle decreases from about 20°to close to 0°,the asymmetric magnetization reversal phenomenon of the rising and falling branches of the hysteresis loop gradually disappears.Through comprehensive analysis of the experimental results,it is believed that the change of the non-collinear angle is related to the distribution of the magnetic moment of the Co layer.(2)In the Pt/Co/IrMn ultrathin film system with perpendicular exchange bias,the effects of AFM layer thickness,FM layer thickness and annealing temperature on the static magnetic and magnetic domain structure of the film were studied.The results show that when the thickness of the IrMn layer reaches to 4 nm,an exchange bias effect appears and there is an unusual double bias phenomenon of the hysteresis loop when the thickness of the IrMn layer reaches to 4.8 nm.With the thickness of the IrMn layer increases,the perpendicular exchange bias field increases firstly and then remains unchangeable,the maximum value can reach to 1269 Oe.Meanwhile,the magnetic domains gradually change from full circular domains to irregular flocculent domains.By changing the thickness of the Co layer,it is found that with the thickness of the Co layer increases,the exchange bias field,the coercivity and interface exchange coupling energies all decrease.In addition,after annealing the film at 100°C,some samples still have double bias.When the annealing temperature reaches to 150°C,all samples have normal unidirectional bias hysteresis loops,and the exchange bias field increase.Meanwhile,the nucleation points of magnetic domains increase and structure of the magnetic domain also undergo relatively significant change.(3)In the(Pt/Co)_n/IrMn multilayer film system with perpendicular exchange bias,the effects of the number of cycles(n)and the measurement temperature(T)on the magnetic properties of the film were studied.The results show that the exchange bias field,the coercivity and remanence ratio all decrease significantly with the number of cycles increases.Meanwhile,the domain nucleation points increase and the boundary become irregular.With the measurement temperature increases,the coercivity and exchange bias field decrease.When the test temperature reaches to 400 K,the exchange bias phenomenon disappears.