| Recently,with the development of composite nanomaterials,core-shell composite materials have aroused a lot of interest due to their rich physics.A variety of topological spin structures can be formed in the core-shell structure materials,where these spin structures can be used as information carriers for next generation nanoscale magnetic storage devices.In this thesis,the nucleation of spin structures in core-shell composite materials is calculated by micromagnetic simulation.The details of research are as follows:1.The demagnetization processes of cylindrical nanowires with soft/hard magnetic core-shell structure are simulated.The hysteresis loops with different shapes and material parameters,and the nucleation processes of spin structures are calculated.It is found that the thicknesses of soft and hard magnetic phases have a certain effect on the magnetization reversal mechanism.Three inversion mechanisms are obtained corresponding to three kinds of spin structures near the coercivity points,which are radial vortex,quasi-coherent state,and vortex,respectively.Besides,the length-diameter ratio of nanowires,the deviations of magnetic crystal anisotropy easy axis and the interfacial coupling strength also impact the demagnetization process.They influence not only the magnetic properties,but also the configurations of spin structures.2.The demagnetization processes of core-shell nanodisks with magnetocrystalline anisotropic defects are simulated.According to the hysteresis loops,variations of spin structures under different external fields are analyzed.It’s found that both the magnetocrystalline anisotropy constants in the defect region and the defect radius would influence the nucleation mechanism of the spin structure and the magnetization reversal mechanism.Three inversion mechanisms are obtained corresponding to three kinds of spin structures near the coercivity points,which are ferromagnetic state,magnetic bubble,and parallel/antiparallel magnetic vortex,respectively.In addition,the nucleation of spin structures in the core-shell nanodisks with Dzyaloshinsky-Moriya interaction(DMI)is simulated.In the absence of external stimulus,skyrmions,which require lower DMI value,as well as kπ-skyrmions,can be formed spontaneously in the core-shell structures.The studies of core-shell composite materials in this thesis are helpful to understand the magnetization reversal mechanism,and also provide a theoretical guidance for exploring new topological spin structures. |
