| Due to the exchange bias between ferromagnetic(FM)and antiferromagnetic(AF)materials,the interface exchange coupling of FM/AF will cause unidirectional magnetic anisotropy in the FM layer and induces a collinear uniaxial magnetic anisotropy,both of them are superimposed on magnetocrystalline anisotropy,determining the magnetic switching process of the FM layer.There is an exchange spring coupling across the interface of FM/FM,however,there are few studies on the magnetization reversal of heterostructures under the exchange spring coupling at the interface.Therefore,in order to better apply FM/AF and FM/FM heterostructures to magnetic devices,it is necessary to study the magnetization reversal process and magnetization mechanism of the heterostructures.Polycrystalline Co Fe thin film with highest intrinsic saturation magnetization and low anisotropy energy constant has been widely used in magnetic recording media and wireless communication devices.B2-ordered Fe Rh undergoes a first-order phase transition from the antiferromagnetic(AF)to the ferromagnetic(FM)state upon heating,which is accompanied by lattice expansion.Co Fe B film with amorphous structure has excellent soft magnetic properties and can be used in spin devices with multilayer structure.Ir Mn has high thermal stability and corrosion resistance,and is an excellent antiferromagnetic material.In this work,the magnetization process of a single-layer FM film,FM/AF and FM/FM heterostructures formed by the combination of the above metal thin films are studied,and the effect of interface coupling on the magnetization reversal and magnetization mechanism are investigated.In this work,we first prepared a single-layer polycrystalline Co Fe(10 nm)film and Co Fe(10 nm)/Fe Rh heterostructures with different thickness of Fe Rh.According to angular dependence of H_c and M_r/M_s,as well as the calculation results based on the Stoner-Wohlfarth(SW)model,we found that the polycrystalline Co Fe film exhibits uniaxial magnetic anisotropy,and the in-plane magnetization mechanism is dominated by coherent rotation.The single Co Fe layer exhibits two-fold magnetic anisotropy.For the Co Fe/Fe Rh heterostructures,regardless of the magnetic state of Fe Rh,the Co Fe layer shows four-fold magnetic anisotropy due to the interface coupling but with a phase shift of 45°after the phase transition occurs.Therefore,the magnetization reversal mechanism of Co Fe/Fe Rh heterostructures is mainly dominated by domain wall nucleation and propagation,which changes greatly compared with the single-layer Co Fe.In addition,we found that the increase in the chemical order of the Fe Rh layer is the key to the increase of its phase transition temperature,and it is also the reason why the magnetization of Fe Rh in ferromagnetic state increases with the thickness.In addition,we also prepared a 10 nm thick amorphous Co Fe B film on a Mg O(001)single crystal substrate,and attempted to epitaxially prepare Co Fe B/Ir Mn/Cr and Co Fe B/Ir Mn/Fe heterostructures on Mg O(001)single crystal substrate using Cr and Fe as buffer layers.It was found that the epitaxial growth of Ir Mn cannot be achieved using Cr as the buffer layer.When Fe is used as the buffer layer,both Fe and Ir Mn can be epitaxially grown well,and then recombine with the amorphous Co Fe B film to form an exchange bias multilayer structure.Three types of hysteresis loops in the amorphous Co Fe B layer are found:biased square hysteresis loops,biased one-side two-step hysteresis loops,unbiased hysteresis loops.Due to the interface coupling effect,the amorphous Co Fe B layer and the single crystal Fe layer exhibit similar four-fold symmetry magnetic anisotropy.The magnetization model of the Co Fe B layer can also be explained by the mechanism of domain wall nucleation and propagation. |
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