Study Of The Effects Of Interfacial States On The Transport And Magnetic Properties In Magnetic Multilayers

Spintronics, based on the manipulation of the electronic spin and charge, has been widely studied and used in information technology and biomedical sensors. As one of the important materials for spintronic devices, the nano-scale magnetic multilayers have been widely studied. For nano magnetic materials, the surface and interface effects which is closely related to the size and dimensions play important roles in its magntic and transport properties. As a result, it is of great importance for the systematic and intensive study of the interface structures (chemical states, interfacial roughness, crystallic states, and so on) on magntic multilayers. As the promising spintronic materials, the NiFe-and Co-based multilayers with diffrent application backgrounds have been constructed. Also, Interfacial manipulation of ferromagnet/oxide and ferromagnet/metal are investigated in optimizing the related transport and magnetic properties. The following researches have been carried out:(1) By intercalating NiO layers to Ta/NiFe and NiFe/Ta interfaces, the planar Hall sensitivity in Ta/NiO/NiFe/NiO/Ta multilayers was increased by 150% compared with that in Ta/NiFe/Ta multilayers. The great improvement of the sensitivity derived from the increase of resistivity change (△ρ) and the decrease of saturation field (Hs). The enhancement of Ap could be attributed to the strengthened spin dependent elastic scattering to the interfacial conductive electrons due to flat oxide/metal interfaces. Meanwhile, the existence of oxide (NiO) prevented the atomic interdiffusion of Ta and NiFe at the interfaces, which led to the easier magnetization rotation of NiFe layer, resulting in lower saturation field.(2) The planar Hall effect in NiFe/Cu/IrMn multilayers was strongly influenced by the Cu spacer thickness (tCu), which was due to the variation of interfacial roughness. With tcu increasing, a peculiar change of planar Hall voltage was observed. The reason for the voltage behaviors was that the interfacial roughness influenced the spin-asymmetry of spin-polarized electrons in ferromagnetic metals. The diffusely scattering to the electrons turned to specular scattering when the interface became flat, leading to the variation of resistivity change (△ρ). As the increase of tCu, the extremum field was reduced because of the weaken exchange coupling between NiFe and IrMn layers. The result provides theoretical reference for the future experiments.(3).An enhancement of planar Hall sensitivity in NiFe/Au/IrMn multilayers was obtained by introducing interfacial modification of Au. The improvement of the sensitivity derived from the increase of resistivity change (△ρ), which was attributed to strengthened spin-asymmetry of polarized electrons in NiFe layer induced by strong spin-orbit scattering of Au layer. Furthermore, the NiFe/Au/IrMn structure based sensor exhibited good thermal stability. The high sensitivity together with good thermal stability makes the NiFe/Au/IrMn structure based sensor very promising for bio-detections.(4) To reveal the underlying mechanism of Mg influence on the enhanced post-annealing stability of perpendicular Ta/CoFeB/Mg/MgO multilayers, the X-ray photoelectron spectroscopy analysis has been performed. It was found that a certain amount of Mg interlayer at the CoFeB/MgO interface could prevent the Ta oxidation, and consequently lower the diffusion motivation of Ta from the bottom layer to the CoFeB/MgO interfaces to some extent in the annealing process. The prevention of Ta diffusion realized the effective hybridization of Fe and O at the CoFeB/MgO interface and maintained interfacial magnetic anisotropy (KCoFeB/Mgo). As a result, the perpendicular magnetic anisotropy at high annealing temperatures was maintained.(5) To decrease the intermixing of Co/Ni multilayers at high annealing temperatures, appropriate thickness of Cu spacer was introduced at the Co/Ni interface. As a result, the perpendicular magnetic anisotropy at the annealing temperature 400℃ was realized, indicating high post-annealing stability of (Co/Ni)n multilayers. X-ray reflectivity results showed that the multilayer structure was kept by introducing Cu at the Co/Ni interface, which was one important reason for the enhanced post-annealing stability of PMA. This is of great interest for out-of-plane magnetized spintronic devices which require to be combined with complementary metal-oxide semiconductor (CMOS).