The Influence Of Pinned Uncompensated Moments Of Antiferromagnetic On The Exchange Bias

The magnetic metal film has a very complicated physical mechanism,its phenomenon is mainly manifested in the coupling effect between the multilayer films and the change of the magnetic resistance caused by the electron spin transport.The research of magnetic thin films has promoted the development of spintronics,occupying an important position in the new generation of spintronics devices.In particular,the spin hall effect and the exchange bias effect of the ferromagnetic(FM)/antiferromagnetic(AFM)interface have been widely used in spintronics devices.Since the discovery of the exchange bias effect,it has been of great significance in the basic scientific exploration of condensed matter physics and spintronics and the design of magnetic field sensors,magnetic recording heads,magnetic random access memory,spin valves.In recent decades,scholars have put a lot of efforts into revealing the physical mechanism of the exchange bias effect.But so far,there is no comprehensive theory to describe the exchange bias effect in detail,this is mainly due to the complexity of its phenomenon and its strong dependence on structure and interface.Earlier models assumed that the entire spin structure of the AFM layer was fixed and all interfacial AFM spins were exchange-coupled with the FM layer.In fact,only about4%of AFM atoms can produce exchange bias effects,which is one of the reasons why the experimental value of the observed exchange bias field(H_eb)differs from the theoretical value by several orders of magnitude.At present,researchers have systematically studied the exchange bias effect of the FM/AFM bilayers interface.However,the study of the coupling effect of the pinned magnetic moments inside the AFM layer and the FM layer needs to be further studied.In this paper,the author systematically studied the magnetic properties of the FM/AFM/FM trilayer films system and experimentally studied the relationship between temperature,cooling field,nonmagnetic intercalation layer and exchange bias field.The effects of AFM layer thickness,top and bottom FM layer intercalation on the pinned magnetic moments and exchange bias effect inside the AFM layer are studied.In this paper,Ni₈₁Fe₁₉/Ni₅₀Mn₅₀,Co₈₁Fe₁₉/Fe₅₀Mn₅₀ bilayers and Ni₈₁Fe₁₉/Ni₅₀Mn₅₀/Ni₈₁Fe₁₉ trilayers were prepared on Si substrates using magnetron sputtering technology.The crystals of the samples were measured by X-ray diffraction,thin film magnetic were measured by vibration sample magnetometers.The main results are listed as following:Firstly,compared with the Ni Fe/Ni Mn/Ni Fe trilayer and Ni Fe/Ni Mn bilayer with the same thickness,the H_eb of the bilayer is larger than that of the trilayer.It shows that in such thin film systems,the exchange bias effect is not only caused by the FM/AFM interface effect.Therefore,it is necessary to investigate the influence and contribution of the pinned magnetic moments inside the AFM layer to the exchange bias.Secondly,effect of the top FM layer thickness on the H_eb of the trilayer Ni Fe/Ni Mn/Ni Fe:for Ni Fe(15 nm)/Ni Mn(15 nm)/Ni Fe(t)trilayers,the H_eb decreases with the thickness of the top Ni Fe layer increases.However,when the thickness of the top layer is large,the value of H_eb remains almost constant.This indicates that the thickness of the top layer will inhibit the generation of the AFM pinned uncompensated moments,resulting in insufficient coupling effect between the pinned uncompensated moments and the FM layer,thereby reducing the exchange bias effect.Thirdly,effect of the bottom FM layer thickness on the H_eb of bilayer and trilayer films:For the Ni Fe(t)/Ni Mn(10 nm)bilayers and Ni Fe(t)/Ni Mn(10 nm)/Ni Fe(15nm)trilayers,the H_eb decreases with the increase of the thickness of the bottom Ni Fe,but it will not remain at a constant value in the end,which shows that the bottom and top FM layers have independent effects on the exchange bias effect.The thickness of the top layer mainly controls the H_eb by suppressing the generation of pinned uncompensated magnetic moments by the AFM layer,while the thickness of the bottom layer has an effect on the exchange bias,the main effect is derived from the intrinsic behavior of the FM layer.Fourth,for the Ni Fe(15 nm)/Ni Mn(t)bilayers and Ni Fe(15 nm)/Ni Mn(t)/Ni Fe(15 nm)trilayers.The H_eb or coercivity(H_C)increases with the thickness of the Ni Mn layer,the highest value is measured when the thickness of the AFM layer is 10 nm.However,when the thickness of the AFM layer continues to increase,both H_eb and H_Cwill decrease,and the H_eb of the trilayer is always lower than that of the bilayer.This indicates that the structure of the magnetic domain depends on the thickness of the AFM layer,the generation of domain walls in the thick AFM layer is energetically disadvantageous.This may directly lead to a reduction in the density of the pinned uncompensated moments,and ultimately to a reduction in the exchange bias effect.Fifth,for the Co Fe(15 nm)/Fe Mn(10 nm)bilayer sample,the H_eb is affected by Cu intercalation,cooling field and measurement temperature.When the Cu interlayer is very thick,the H_eb decreases linearly with the thickness of Cu;the H_eb increases first and then decrease with the increase of the cooling field;the H_eb decreases linearly with the measurement temperature and then remains constant.The above experimental results show that:for Ni Fe/Ni Mn/Ni Fe trilayer,the pinned uncompensated moments are widely distributed inside the AFM layer,the thickness of the top FM layer and the AFM layer both affect the distribution density of the pinned uncompensated moments inside the AFM layer,thereby affecting the exchange bias.Therefore,the exchange bias effect is not only an interface effect,but also sometimes produces a bulk effect,or a combination of an interface effect and a bulk effect.The research in this paper will help to deepen the understanding of the physical mechanism of the exchange bias effect.The adjustment of the exchange bias can be achieved by adjusting the pinned uncompensated moment of the AFM layer,and the spintronics based on the exchange bias Device design has a certain positive role in promoting.