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ELECTRONIC STRUCTURE AND CRYSTALLINE ELECTRIC FIELD IN Rco5(R= Y,La, Ce,Pr, Nd,Sm, Gd,and Tb) 下载免费PDF全文
Self consistent charge and spin polarized local spin-density approximation functional theory calculations based on the discrete variational method have been performed for RCo5(R=Y, La, Ce, Pr, Nd, Sm, Gd, and Tb) compounds. The partial density of states of the Pr atom in the PrCo6Co12 cluster is established to be strikingly similar to that of the Ce atom in the CeCo6Co12 cluster, supporting the suggestion that the Pr atom is valence fluctuating. The radii <r4f> and <r4f2> of the 4f electrons of the R atom from La to Tb, except Ce, show the lanthanide contraction. The crystalline electric field (CEF) parameter A02 at the R site is calculated using a real charge distribution ρ(R) in the cluster, except for Pr and Nd, and is in agreement with that evalu ated based on the single-ion model. This result shows that the CEF parameter A02 is mainly determined by the near electronic structure. There exists a hybridization in a certain degree between the light rare-earth R-4f and Co-3d orbitals in some single-electron-molecular-orbitals, which are n ear the Fermi energy level and occupied by electrons. For light rare-earths the R-4f electrons in R Co6Co12(R=Y, La, Ce, Pr, Nd, and Sm) clu sters are not localized entirely and a small amount of the R-4f electrons have itinerant properties. 相似文献
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INTER-GRAIN EXCHANGE INTERACTION FOR SINGLE-PHASE NANOCRYSTALLINE Nd-Fe-B MAGNETS 总被引:1,自引:0,他引:1 下载免费PDF全文
The demagnetization curve as a function of intensity of the inter-grain exchange interaction was calculated for single-phase nanocrystalline Nd-Fe-B magnets by use of the finite-element technique of micromagnetics. Also, the strength of the exchange interaction was estimated as a function of the Nd content x for the nanocrystalline NdxFe94-xB6 magnets by comparing the above result with the experimental relation between iHc and x for the magnets. We found that the inter-grain exchange interaction decreases with the increase of x, are ≈70% and ≈60% of the inter-grain exchange interaction for x=15.5(μ0iHc≈2.0T) and x=19(μ0iHc≈2.3T), respectively. 相似文献
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In this paper magnetization remanence curves were studied for nanocrystalline Pr8Fe87B5, Pr12Fe82B6 and Pr15Fe77B8. Initially the sample was at remanence following saturation along z-axis. After rotating the magnet by 5n degrees (n=0, 1, ..., 18) a field H was applied along z-axis and then decreased to zero, and the remanence Jr^n was measured as a function of H. The curves were compared with those calculated based on the nucleation of reverse domain model and domain wall pinning model. The latter model succeeds in simulation much better than the former, and it is concluded that the magnetization reversal is dominated by domain wall pinning for all the samples. The nucleation mechanism contribution, while remains small, increases with the increase of Pr content. 相似文献
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ELECTRONIC STRUCTURE AND CRYSTALLINE ELECTRIC FIELD IN Rco5(R= Y, La, Ce, Pr, Nd, Sm, Gd, and Tb) 下载免费PDF全文
Self consistent charge and spin polarized local spin-density approximation functional theory calculations based on the discrete variational method have been performed for RCo5(R=Y, La, Ce, Pr, Nd, Sm, Gd, and Tb) compounds. The partial density of states of the Pr atom in the PrCo6Co12 cluster is established to be strikingly similar to that of the Ce atom in the CeCo6Co12 cluster, supporting the suggestion that the Pr atom is valence fluctuating. The radii <r4f> and <r4f2> of the 4f electrons of the R atom from La to Tb, except Ce, show the lanthanide contraction. The crystalline electric field (CEF) parameter A02 at the R site is calculated using a real charge distribution ρ(R) in the cluster, except for Pr and Nd, and is in agreement with that evalu ated based on the single-ion model. This result shows that the CEF parameter A02 is mainly determined by the near electronic structure. There exists a hybridization in a certain degree between the light rare-earth R-4f and Co-3d orbitals in some single-electron-molecular-orbitals, which are n ear the Fermi energy level and occupied by electrons. For light rare-earths the R-4f electrons in R Co6Co12(R=Y, La, Ce, Pr, Nd, and Sm) clu sters are not localized entirely and a small amount of the R-4f electrons have itinerant properties. 相似文献
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在制备出Gd3(Fe1-xCox)29-yCry化合物基础上,成功制备出Sm3(Fe1-xCox)29-yCry化合物,通过x射线衍射和热磁分析对R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性进行了研究,利用原子半径的几何因素解释了高Co含量3:29型化合物必须要有较多稳定元素的原因.对于不同的稳定元素,稳定元素半径越大,所需稳定元素含量越少,可是稳定元素的半径愈大,其增大晶格常数的能力愈强,这反而不利于稳定3:29相.通过对R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性的研究,成功地制备出具有室温单轴磁晶各向异性的Gd3(Fe1-xCox)29-yCry(0.4≤x≤1.0;4.0≤y≤6.5)及新的Sm3(Fe1-xCox)29-yCry(0.4≤x≤1.0;4.5≤y≤7.5)化合物. 相似文献
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The demagnetization process for a Nd2Fe14B grain covered by an α-Fe layer was studied by use of the finite element technique of micromagnetics. μ0iHc decreases with the increase of α-Fe layer thickness t. With the increase of t from 0 to 6nm, μ0iHc decreases from ~7 T to ~3.5 T when the angle between the applied field and the c-axis of the Nd2Fe14B grain is 0.5° and from ~4 T to ~1.5 T when the angle is 30° or 60°. The effect is only slightly affected by the angle between the α-Fe layer and the field direction. 相似文献
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通过X射线衍射分析和磁性测量研究了化合物YCo12-xTix和YFe12-xTix的结构与磁性.结果表明,化合物YCo12-xTix和YFe12-xTix均具有ThMn12型结构,室温下为单轴磁晶各向异性.随着Ti含量的增加,YCo12-xTix的居里温度Tc显著降低,而YFe12-xTix的居里温度Tc几乎不变.所有化合物的饱和磁化强度Ms和磁晶各向异性场Ha随着Ti含量的增加而降低,这可以用双次晶格模型来解释. 相似文献
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ANISOTROPIC CHARACTERISTICS OF DEMAGNETIZATION CURVE FOR NANOCRYSTALLINE Nd-Fe-B MAGNET CALCULATED BY MICROMAGNETICS 下载免费PDF全文
The demagnetization curves for nanocrystalline Nd-Fe-B magnets of a stoichiometric composition were calculated by making use of the finite element technique of micromagnetics. The curve, especially iHc, varies in a wide range with the direction of applied field if the grain number N is taken to be small. With the increase of N, the range becomes smaller and the average of iHc decreases and approaches a limit iHc(N=∞). iHc for finite N is larger than, or at least equal to, iHc(N=∞). Jr/Js is weakly affected by N and the field direction. Jr/Js(N=∞) decreases with the increase of grain size L. These are larger than the experimental values for the Nd-rich Nd2.33Fe14B1.06Si0.21 magnets by ~0.05. iHc(N=∞) increases with the increase of L, and is close to or somewhat smaller than the experimental values of the Nd-rich magnet, as would be expected. In contrast, the curve calculated for the non-interacting grain system (Stoner-Wohlfarth model) of N≥30 depends neither on the field direction nor on N. 相似文献