The Studies Of Two-phased Nanocomposite Magnetic Films Of Nd₂Fe₁₄B/α-Fe

The permanent magnets have taken an important role in our lives, and theirapplications are coming into all aspects of our lives. Further, the scopes of applications have beenmore and larger. The exchange-coupled magnets are the composite materials which enclosed hardlayers and soft layers, and the hard and soft phases are exchange-coupled in nanoscale so that theyexhibit a spring behavior. With large coercivity provided by the hard phase and large remanenceprovided by the soft phase, the exchange-coupled magnets have larger magnetic energy product.At the same time, these materials also have another nature such as magneto-resistor and verticalexchange coupling which have caused extensive research both at home and abroad. This workstudies the magnetic property of the Nd2Fe14B/α-Fe bilayers based on OOMMF software (3D) and1D method. We researched the macroscopic hysteresis, coercivity field, pinning filed andnucleation. It is found that there exist three-step magnetic reversals processes, which arenucleation, growth and displacement of the domain and this three-step process. The main work isas follows:1. Take the Nd2Fe14B/α-Fe bilayers which the magnetization axis is parallel to the film asexample, we studied the magnetic property of the magnetic bilayers base on OOMMF software(3D) and1D method. We found that the nucleation and coercivity field decrease with the increaseof the Ls. While the results calculated by OOMMF are systematically smaller than the resultsbased on1D method. On the other hand, the highest (BH)maxis around595kJ/m3when thethickness of the soft layer is5nm.2. Take the Nd2Fe14B/α-Fe bilayers which the magnetization axis is perpendicular to the filmas example, we studied the changes of the nucleation and coercivity field with the increase of thesoft layer. With the calculation by both OOMMF and1D method, we found that the critical fieldscalculated by the two methods are very similar, i.e. the critical fields decrease with the increase ofthe thickness of the soft layer. Furthermore, it changes fast when the Lsare small while tend to be aconstant value when the Lsare large. On the other hand, we found that maximum energy productsincrease when the Lsare small whilst decrease when Lsare large, and the highest (BH)maxis around540kJ/m3when the Ls=1nm. The further calculation shows that the (BH)maxbased on the3D method is systematically smaller than the results calculation by the1D method.3. Through the research of the magnetic moment distribution at the film plane in themagnetization reversal process, we found that the magnetic moments at the edge and corner startto deviate from the previous saturation state firstly whilst the moments at other places still orient atthe previous saturation state. With the decrease of the applied field, the moments at other placesbegin to deviate, and the reversals of the magnetic moments extend to all the bilayers. It is calledthe corner effect in our work. On the other hand, we found there is a formation and annihilation ofvortex on the process when the magnetocrystalline axes of both layers and the applied field areassumed to be in the z directions.