Micromagnetic Study Of Nd₂Fe₁₄B/α"-（FeCo）₁₆N₂ Nanocomposites

With the advancement of technology,rare earth permanent magnet materials have been developed and used in many fields rapidly.However,due to the scarcity of rare earth resources,scientists have tried to replace them.The exchange coupling hard/soft magnetic materials have attracted substantial interests.This material has the advantages of large coercivity of hard phase and high saturation magnetization of the soft phase.It can greatly decrease the use amount of rare earth elements and it is expected to become a new generation rare earth permanent magnet materials with high development prospect.As is well-known that Nd₂Fe₁₄B is called―permanent magnet king‖by its large magnetocrystalline anisotropy,whileα′′-（FeCo）₁₆N₂ has a high saturation magnetization and it is a good candidate for soft magnetic materials.In this paper,Nd₂Fe₁₄B/α"-（FeCo）₁₆N₂ was used as the research object,and the three dimensional micromagnetic simulation software OOMMF was used to study the influence of the magnetic properties of the system of interface layer formed by the diffusion and the insertion of nonmagnetic spacer layer in Nd₂Fe₁₄B/α"-（FeCo）₁₆N₂ bilayers.In addition,the effect of the size on the magnetic properties of the composite nanorods of two strctures had been calculated.The main research contents are as follows:（1）The effect of the interface layer formed by the diffusion is discussed on the magnetic properties of the Nd₂Fe₁₄B/α"-（FeCo）₁₆N₂ bilayers.Hysteresis loops of different interface layer thicknesses are calculated when the total thickness of the composite film was fixed.It was found that the formation of the interface layer can decrease the coercivity of the system drastically.The reason why is that the interface layer formed by the diffusion changes the interface characteristics,and the existence of the interface layer will reduce the difference in parameters between the magnetic layers,and the whole system is easier to deviate.The hysteresis loops at different thicknesses of the interface layer were also calculated when the thickness of the hard magnetic layer and soft magnetic layer are constant.It was found that as the thickness of the interface layer increases,the coercivity and magnetic energy product of the system decrease continuously.The coercivity is the main factor that affects the magnetic energy product,the existence of the interface layer is not conducive to the improvement of the magnetic properties of the Nd₂Fe₁₄B/α"-（FeCo）₁₆N₂ bilayers.（2）In order to prevent the formation of interface layer,we try to insert a thin nonmagnetic spacer layer in Nd₂Fe₁₄B/α"-（FeCo）₁₆N₂ bilayers.The hysteresis loops,magnetic reversal processes,and energy variation of exchange-coupled Nd₂Fe₁₄B/α′′-（FeCo）₁₆N₂bilayers inserted with a nonmagnetic spacer layer were systematically investigated.The effect of different contact areas（CAs）on the coercivity of the system was studied.The results show that the insertion of the nonmagnetic spacer layer can greatly improve the coercivity of the system.When the contact area was 16%,the coercivity was about three times larger than that of soft/hard bilayers.In addition,the effects of a deviation angleβbetween the easy axis and the applied field,different thickness of soft layer L^S and the interface exchange coupling constant A^hs on the magnetic properties of the system were further studied.Furthemore,the magnetization reversal process was also studied.Finally,the influence of the insertion of the nonmagnetic spacer layer on the energy change of the system was compared.（3）The effect of the size on the magnetic properties of the composite nanorods of two strctures has been calculated.For the composite nanorod with hard ring and soft rod structure,the diameter of the inner rod was fixed,the magnetic properties were reduced continuously with the increase of the thickness of the outer ring;After selecting the appropriate outer ring thickness,the magnetic properties were improved with the increase in the diameter of the inner rod.Because the diameter of the inner rod increases,the composition of the soft magnetic phase increases.In the composite nanorod with soft ring and hard rod structure,when the diameter of the inner rod was fixed,the magnetic properties of the composite nanorod were improved continuously as the thickness of the outer ring increases due to the system shows the characteristics of soft phase;When the thickness of the outer ring is constant,the magnetic properties of the composite nanorod decrease continuously with the increase of the diameter of the inner rod.