Taking Nd2Fe14B/α-Fe as example, the exchange-coupling interactions between magnetically soft and hard grains in nanocomposite permanent materials and their effects on the effective anisotropy of materials were inves...Taking Nd2Fe14B/α-Fe as example, the exchange-coupling interactions between magnetically soft and hard grains in nanocomposite permanent materials and their effects on the effective anisotropy of materials were investigated. The calculation results expressed that the exchange-coupling interactions are enhanced with the reduction of grain size, and the effective anisotropy of materials decreases with the reduction of gram size and the increase of magnetically soft phase component. The remanence and the effective anisotropy of materials possess the opposite variation trend with the change of grain size and phase ratio. The mean grain size should be in the range of 10-15 nm and the ratio of soft phase should be less than 50% for getting the magnet with high energy product.展开更多
The effect of exchange-coupling interaction on the effective anisotropy and its varying tendency in nanocrystalline single-phase NdFeB permanent magnetic material have been investigated. The results show that the exch...The effect of exchange-coupling interaction on the effective anisotropy and its varying tendency in nanocrystalline single-phase NdFeB permanent magnetic material have been investigated. The results show that the exchange-coupling interaction between grains makes the effective anisotropy of material, Keff, decrease with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease in effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline single-phase NdFeB permanent magnetic material. In order to get high anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent material, the grain size should be larger than 35 nm.展开更多
The coercivity of NdFeB magnets is determined by the coercivity of individual grains and the interaction between the grains composed of the magnets. The coercivity of individual grains and the intergrain interaction d...The coercivity of NdFeB magnets is determined by the coercivity of individual grains and the interaction between the grains composed of the magnets. The coercivity of individual grains and the intergrain interaction depend on the degree of the grain alignment, “tanθ type” Gaussian function is applied to describing the degree of the grain alignment. According to different coercivity mechanisms, there are different formula on the coercivity and the angular dependence of coercivity. The interaction between grains can be classified as the long-range magnetostatic interaction and the exchange-coupling interaction of neighboring grains. For the sintered magnet, the grain size is large and the grain boundaries are mostly separated by the non-magnetic phase. So, the long-range magnetostatic interaction is much stronger than the exchange coupling interaction and it makes the coercivity of the magnet composed of misaligned grains be bigger than that of the magnet composed of ideally aligned grains. The effects of coercivity of individual grains and the intergrain interactions are taken into account, and the starting field theory is in agreement with the experimental result for the coercivity of sintered NdFeB magnets.展开更多
Taking nanocrystalline Nd_2Fe_(14)B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of eff...Taking nanocrystalline Nd_2Fe_(14)B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of effective anisotropy constant K_(eff) on grain size was investigated. Calculation results reveal that the exchange-coupling interaction enhances and the effective anisotropy of material K_(eff) decreases with the reduction of grain size. The variation of K_(eff) is basically the same as that of coercivity. The decrease of effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline Nd_2Fe_(14)B permanent magnetic material.展开更多
Electroless CoNiWP magnetic films were prepared by varying the bath pH and then characterized by energy dispersive X-ray analysis, X-ray diffraction and magnetic force microscopy, it has been found that the microstruc...Electroless CoNiWP magnetic films were prepared by varying the bath pH and then characterized by energy dispersive X-ray analysis, X-ray diffraction and magnetic force microscopy, it has been found that the microstructure and the magnetic properties of films were influenced greatly by the bath pH. At the bath pH 8.06, the grain size and coercivity of the films reach maximuml while the squareness （Mr/Ms） of MH curves reaches minimum. The Henkel plots indicates that the exchange-coupling interaction is very weak at this pH, which may be caused by phase-separation and large grain size, and then results in the lowest squareness. At pH above 8.5, obvious exchange-coupling interaction is observed because of the inexistence of phase-separation and the refinement of grain size.展开更多
Taking α-Fe and Nd_2Fe_(14)B grains as example, the grain size dependence of the exchange-coupling interaction and effective anisotropy and also their variations depending on the ratio of magnetically soft and hard g...Taking α-Fe and Nd_2Fe_(14)B grains as example, the grain size dependence of the exchange-coupling interaction and effective anisotropy and also their variations depending on the ratio of magnetically soft and hard grain sizes, D_s∶D_h, were investigated. When grain size D>L_(ex), the grain’s anisotropy is the statistic value of the coupled and uncoupled part. The anisotropy constant of uncoupled part is the common value K_1 and that of coupled part varies with the distance to the grain surface. The effective anisotropy constant between magnetically soft and hard grains, K_(eff), can be expressed as the sum of the products of volume fractions for soft and hard grains, respectively, and the corresponding mean anisotropy constants. The calculation results indicate that the exchange-coupling interaction is enhanced with the reduction of grain size, and the effective anisotropy decreases with reducing grain size and increasing ratio of D_s∶D_h. In order to get high effective anisotropy constant, K_(eff), in composite magnetically soft-hard grains, the hard grain size should be larger than 30 nm and the soft grain size should be about 10 nm.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant No. 59971026)the Science Foundation of Shandong Province (Grant No. Y2000F10).
文摘Taking Nd2Fe14B/α-Fe as example, the exchange-coupling interactions between magnetically soft and hard grains in nanocomposite permanent materials and their effects on the effective anisotropy of materials were investigated. The calculation results expressed that the exchange-coupling interactions are enhanced with the reduction of grain size, and the effective anisotropy of materials decreases with the reduction of gram size and the increase of magnetically soft phase component. The remanence and the effective anisotropy of materials possess the opposite variation trend with the change of grain size and phase ratio. The mean grain size should be in the range of 10-15 nm and the ratio of soft phase should be less than 50% for getting the magnet with high energy product.
基金the National'863'Project of China(Grant No.2002AA324050)the National Natural Science Foundation of China(Grant Nos.9971026)the Nature Science Foundation of Shandong Province(Grant No.Y2000F10)
文摘The effect of exchange-coupling interaction on the effective anisotropy and its varying tendency in nanocrystalline single-phase NdFeB permanent magnetic material have been investigated. The results show that the exchange-coupling interaction between grains makes the effective anisotropy of material, Keff, decrease with the reduction of grain size. The variation of Keff is basically the same as that of coercivity. The decrease in effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline single-phase NdFeB permanent magnetic material. In order to get high anisotropy and coercivity in nanocrystalline single-phase NdFeB permanent material, the grain size should be larger than 35 nm.
基金Project supported by the National Natural Science Foundation of China (Grant No. 59571017)
文摘The coercivity of NdFeB magnets is determined by the coercivity of individual grains and the interaction between the grains composed of the magnets. The coercivity of individual grains and the intergrain interaction depend on the degree of the grain alignment, “tanθ type” Gaussian function is applied to describing the degree of the grain alignment. According to different coercivity mechanisms, there are different formula on the coercivity and the angular dependence of coercivity. The interaction between grains can be classified as the long-range magnetostatic interaction and the exchange-coupling interaction of neighboring grains. For the sintered magnet, the grain size is large and the grain boundaries are mostly separated by the non-magnetic phase. So, the long-range magnetostatic interaction is much stronger than the exchange coupling interaction and it makes the coercivity of the magnet composed of misaligned grains be bigger than that of the magnet composed of ideally aligned grains. The effects of coercivity of individual grains and the intergrain interactions are taken into account, and the starting field theory is in agreement with the experimental result for the coercivity of sintered NdFeB magnets.
基金Supported by the National Natural Science Foundation of China(11174004)the Natural Science Key Foundation of Education Departmerct of Anhui Province(KJ2010A012)the Open Foundation of Anhui Key Laboratory of Information Materials and Devices,the"211 Project"of Anhui University
基金Project supported by National‘863’Project (2002AA324050 2002AA302602) and Natural Science Foundation of China(50371046) and Doctoral Foundation of China (20040422014)
文摘Taking nanocrystalline Nd_2Fe_(14)B as a typical sample, based on Herzer′s random anisotropy theory and the cubic grain model, the partial exchange-coupling interaction model was established and the dependence of effective anisotropy constant K_(eff) on grain size was investigated. Calculation results reveal that the exchange-coupling interaction enhances and the effective anisotropy of material K_(eff) decreases with the reduction of grain size. The variation of K_(eff) is basically the same as that of coercivity. The decrease of effective anisotropy is the main reason of the reduction of coercivity for nanocrystalline Nd_2Fe_(14)B permanent magnetic material.
基金the National Natural Science foundation of China under grant No.50572083.
文摘Electroless CoNiWP magnetic films were prepared by varying the bath pH and then characterized by energy dispersive X-ray analysis, X-ray diffraction and magnetic force microscopy, it has been found that the microstructure and the magnetic properties of films were influenced greatly by the bath pH. At the bath pH 8.06, the grain size and coercivity of the films reach maximuml while the squareness （Mr/Ms） of MH curves reaches minimum. The Henkel plots indicates that the exchange-coupling interaction is very weak at this pH, which may be caused by phase-separation and large grain size, and then results in the lowest squareness. At pH above 8.5, obvious exchange-coupling interaction is observed because of the inexistence of phase-separation and the refinement of grain size.
文摘Taking α-Fe and Nd_2Fe_(14)B grains as example, the grain size dependence of the exchange-coupling interaction and effective anisotropy and also their variations depending on the ratio of magnetically soft and hard grain sizes, D_s∶D_h, were investigated. When grain size D>L_(ex), the grain’s anisotropy is the statistic value of the coupled and uncoupled part. The anisotropy constant of uncoupled part is the common value K_1 and that of coupled part varies with the distance to the grain surface. The effective anisotropy constant between magnetically soft and hard grains, K_(eff), can be expressed as the sum of the products of volume fractions for soft and hard grains, respectively, and the corresponding mean anisotropy constants. The calculation results indicate that the exchange-coupling interaction is enhanced with the reduction of grain size, and the effective anisotropy decreases with reducing grain size and increasing ratio of D_s∶D_h. In order to get high effective anisotropy constant, K_(eff), in composite magnetically soft-hard grains, the hard grain size should be larger than 30 nm and the soft grain size should be about 10 nm.
