Research On The Effect Of Interface Characteristics On Magnetic Properties Of Hard/Soft Magnetic Exchange-Coupled Permanent Magnets Based On The Micromagnetic Theory

With the development of science and technology,rare earth permanent magnets are important function materials of modern industry and its market share increases year by year.The strong demand for high-performance rare earth permanent magnets leads to a substantial rise in the consumption and cost of rare earth resources.Therefore,in order to protect the natural environment and realize the development of green and sustainable for permanent magnet resources.It is an inevitable result that research on high-performance permanent magnet materials containing less rare earth elements.Hard/soft magnetic nanocomposite permanent magnets as the one of such the key materials,which are expected to become the fourth generation of rare earth permanent magnets after Nd₂Fe₁₄B permanent magnet.Experimental studies have found that the interface characteristics are important factors affecting the magnetic properties of hard/soft exchange-coupled magnets.The influence of the interface layer formed by the atomic diffusion at the interface and interface anisotropy on magnetic properties for the hard/soft exchange-spring system are analyzed based on three-dimensional micromagnetic numerical simulations and one-dimensional analytical calculations support each other.The underlying physics of this experimental phenomenon are clarified by the spatial distribution of spin,nucleation and pinning provides a theoretical basis for improving the magnetic properties in the experiment.The main researches of this paper are as follows:1.Based on three-dimensional micromagnetic numerical simulations and one-dimensional analytical calculations,the influence of the interface layer formed by the atomic diffusion at the interface on magnetic properties Sm Co/Fe multilayers is researched.Comparing the results of the two micromagnetic methods,it is found that with the increases of the interface layer thickness,its nucleation happens a gradual transition from the first quadrant to the second quadrant,remanence first rises and then drops,but the nucleation field gradually rises,the coercivity increases first and then is almost constant,and hence the maximum energy product increases gradually.The above results calculated by the two methods are in good agreement.During the demagnetization,the spin deviation within the film plane:the three-dimensional numerical simulation shows a progress of generation and disappearance of vortex state,however,the spin deviation within the film plane calculated by the one-dimensional analytical method are coherent.In addition,The nucleation field as a function of the interface exchange energy constant obtained by three-dimensional numerical simulation indicate that with the interface exchange coupling constant increases,the nucleation field rises,the existence of an interface layer between the hard and soft layers enhances the exchange coupling interaction between Sm Co/Fe multilayers.The one-dimensional analytical model established in this chapter is qualitatively consistent with the relevant experimental results[2007 Appl.Physics.Lett.91072509].2.Based on three-dimensional micromagnetic numerical simulation,the influence of the interface layer formed by the atomic diffusion at the interface on magnetic properties in parallel and perpendicular Sm Co/Fe bilayers is researched.For the parallel system,whose nucleation occurs in the second quadrant,as the interface layer thickness increases,though the remanence decreases gradually,the nucleation field and the pinning field increase gradually,and hence the maximum energy product goes up first and then goes down.As a result,the system occurs transitions from the exchange-spring to the rigid magnet.For the perpendicular system,with the increases of the interface layer thickness,its nucleation happens a gradual transition from the first quadrant to the second quadrant.Although the pinning field decreases,is unchanged and increases,the nucleation field and remanence gradually rises.Therefore,the energy product enhance gradually.During the demagnetization,the spin deviation within the film plane:the parallel system shows a progress of generation and disappearance of the flower and C states;however,the perpendicular system shows that of the vortex state.With the increase of the ratio of the Sm Co atomic diffusion in the interface layer of parallel Sm Co/Fe bilayers,the nucleation and pinning fields go up,but the remanence decreases,and hence the maximum energy product first rises and then drops.For the two easy axis orientations and any interface layer thickness,the nucleation field rises with the interface exchange energy constant,indicating that the existence of an interface layer between the soft and hard layers enhances the exchange coupling interaction between them,this is qualitatively consistent with the theoretical results in the previous chapter.The model in this paper well simulates related experimental results[2007 Appl.Phys.Lett.91 072509].3.Based on three-dimensional micromagnetic numerical simulations and one-dimensional analytical calculations,the influence of the interface anisotropy on magnetic properties in the perpendicular Nd₂Fe₁₄B/Fe multilayers is researched.The results of the two methods indicate that when the soft layer thickness is very thin,the influence of the interface anisotropy on the nucleation,pinning and coercivity fields is very obvious.However,as the soft layer thickness increases,the pinning and coercive fields are almost unchanged with the increment of interface anisotropy though the nucleation field still monotonically rises.Negative interface anisotropy decreases the maximum energy products and rises slightly the angles between the magnetization and applied field.In addition,the three-dimensional numerical simulation shows a progress of generation and disappearance of vortex state.The results of the above two models are in good agreement with each other.Simulation results suggest that negative interface anisotropy is necessarily avoided experimentally.