| Permanent magnetic material was applied in our life. Rare earth resources are very limited. Many theoretical and experimental works have been done in this area to find the ideal composite material with huge energy product. The exchange-coupled hard/soft composite magnetic material was coupled the advantage of hard phase to provide large coercivity and the soft phase to provide high saturation. The system comprises hard and soft magnetic properties. This system indicated to lead to large energy product. The characteristics of the material, shape, layer thickness, structure of the system and easy axis orientations should be considered to obtain an appreciable energy product. Nd2Fe14B is considered a high-performance hard magnetic material given its large magnetocrystalline anisotropy. Thus, we choose Nd2Fe14B as the hard phase of the system in this study. The?"-Fe6N2 possesses a giant magnetic characteristic which makes it a prior candidate for soft material. However, ?"-Fe16N2 is difficult to prepare because of the limitations from the FeN phase diagrams. According to our previous study, the addition of Co could enhance the formation of ?"-Fe16N2. Thus, ?"-(FeCo)16N2 was set as the soft phase. In addition, hard-layer and soft-layer thicknesses have a significant effect on the magnetic properties. In the experiment, 8 nm Nd2Fe14B film showed the significant magnetic property to achieve the expected energy product of the exchange-coupled system. Thus,we set the thickness of Nd2Fe14B as 8 nm. For the thickness of the soft layer, we obtained the optimum thickness by using our calculation. In this study, three -dimensional micromagnetic simulation has been performed by OOMMF to investigated exchange-coupled Nd2Fe14B/?"-(FeCo)16N2 system in terms of the shape of the system,soft-layer thickness, the structure of the system and easy axis angle ?. Main results for this work are as follows:(1) We have calculated the magnetic properties of three basic models, the cubic,cylinder and ring. It is found that the cubic modle is the optimal structure of three basic modle. We have further investigated cubic system in terms of soft-layer thickness.(2) Keep the whole hard and soft thickness of bilayer and trilayer system at 8 and 7 nm, respectively, we have calculated the hysteresis loops of the Nd2Fe14B(8 nm)/?"-(FeCo)16N2(7 nm) bilayer system and Nd2Fe14B(4 nm)/?"-(FeCo)16N2(7 nm)/Nd2Fe14B(4 nm) trilayer system to obtain the optimal structure of the exchange-coupled system with the significant energy product. The energy product of the trilayers is determined to be significantly larger than that of the bilayers. The advantage of the trilayers may be owing to the double-sided pinning for the two exchange interfaces,whereas a single pinning is observed in the bilayers. We focused on the structure of trilayer system given that it presents more significant magnetic properties than the bilayer system. We have calculated the magnetic properties through a variety of structure for trilayer system. We also investigated the effect of ? and Ahs on the magnetic properties of the trilayer system.(3) When the whole thickness of system remains constant, we have studied the multilayer systems with different number of layers and the different cycle multilayer systems with the bilayer cell. |
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