| In recent years,magnetic skyrmion has become a hot topic in the field of condensed matter physics,and is attracting extensive attention from researchers in the field of magnetism and topology physics.Magnetic skyrmion is a topologically nontrivial spin structure,it shows great potential as information carrier owing to their topological stability,nanoscale geometry size and smaller driven current density.Magnetic skyrmion is of great significance to the development of the next generation spintronic memory and logic devices.In order to realize the processing of information based on magnetic skyrmion,we must be able to effectively control the creation and annihilation of them,as well as their position and spatial arrangement.However,their existence in ferromagnetically coupled multilayers is spatially disordered arrangement as reported,which hinders the development of skyrmion based racetrack memory and magnonic crystal.Although the artificial skyrmion can solve the problem of spatially ordered arrangement,its size is limited by the physical size of the top nanodisk and cannot be tuned.In this thesis,a nucleation scenario of ordered skyrmions with size tunability in nanostructured synthetic antiferromagnetic?SAF?multilayers is proposed and experimentally verified.Magnetic imaging,magneto-optical Kerr,hall resistance measurement and micromagnetic simulation were used to make a research of the generation mechanism,size tunability and thermal stability of artificial skyrmion in nanostructured SAF multilayers.Firstly,we studied the magnetic properties of synthetic multilayers.We experimentally investigated the thermal stability of the interlayer exchange coupling field Hex and strength Jiec in SAF[Pt/Co]2/Ru/[Co/Pt]4 multilayers with perpendicular magnetic anisotropy.By changing the thickness of the non-magnetic spacing ruthenium?Ru?layer,we find that the Jiec of the multilayer is very sensitive to the thickness of Ru and the property of Jieccan be transformed from ferromagnetic(Jiec>0)to antiferromagnetic(Jiec<0).In addition,temperature-dependent Hex was studied by measuring the magnetization hysteresis loops in the temperature range from 100 K to600 K.It is found that the interlayer exchange coupling of the[Pt/Co]2/Ru/[Co/Pt]4multilayers is not only very sensitive to temperature but also has very high thermal stability.Secondly,we proposed and experimentally demonstrated a nucleation scenario of ordered artificial skyrmion in nanostructured SAF multilayers.Direct magnetic microscope imaging,indirect magnetization curve measurement by magneto-optic Kerr,indirect measurement of hall resistance of electrical transport and micromagnetic simulation were used to verify this mechanism.Instead of relying on Dzyaloshinskii–Moriya interaction,the proposed mechanism depends on the competition between the antiferromagnetic interlayer exchange coupling field in SAF multilayers,the demagnetizing field of the top nanodisk,and the external magnetic field.The artificial skyrmion produced by this new mechanism is not only ordered but also tunable by external magnetic field.Finally,we investigated the robustness of the proposed artificial skyrmion nucleation scenario.By changing the temperature?4.5?300 K?of experiment environment and the diameter?400?1200 nm?and spatial arrangement of the top nanodisks,we find that the proposed artificial skyrmion nucleation scenario is robust against the temperature and the dimension and the spatial arrangement of the top nanodisks. |
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