ELECTRONIC STRUCTURE AND CRYSTALLINE ELECTRIC FIELD IN Rco5(R= Y,La, Ce,Pr, Nd,Sm, Gd,and Tb)

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 ＜r_4f＞ 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.     

固体线膨胀系数测定实验的改进

针对固体线膨胀系数测定实验中样品所处温度梯度场过大、升温和降温速率控制精度低的问题,提出了实验改进的措施.阐述了减小实验样品的温度场梯度,用设定程序控制实验样品的升温、恒温和降温的实施过程,并对金属样品线膨胀系数测定实验结果进行了分析,取得了固体线膨胀系数测定实验的改进设计的预期效果.     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

在制备出Gd₃(Fe_1-xCo_x)_29-yCr_{y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-x< /sub>Co x)29-yCry 关键词： 3(Fe1-xCox)29-yCry化合物')" href="#">R3(Fe1-xCox)29-yCry化合物 相结构 单轴磁晶各向异性}     

Angular dependence of coercivity of grains in nanocrystalline permanent magnets

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.     

INTER-GRAIN EXCHANGE INTERACTION FOR SINGLE-PHASE NANOCRYSTALLINE Nd-Fe-B MAGNETS

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 Nd_xFe_94-xB₆ magnets by comparing the above result with the experimental relation between _iH_c 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(μ_0iH_c≈2.0T) and x=19(μ_0iH_c≈2.3T), respectively.     

EFFECT OF α-Fe SURFACE LAYER ON THE MAGNETIC REVERSION PROCESS FOR Nd2Fe14B CRYSTAL

The demagnetization process for a Nd₂Fe₁₄B grain covered by an α-Fe layer was studied by use of the finite element technique of micromagnetics. μ_0iH_c decreases with the increase of α-Fe layer thickness t. With the increase of t from 0 to 6nm, μ_0iH_c 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.     

R3(Fe1-xCox)29-yCry(R=Gd,Sm)化合物相稳定性研究

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.     

ELECTRONIC STRUCTURE AND CRYSTALLINE ELECTRIC FIELD IN Rco5(R= Y, La, Ce, Pr, Nd, Sm, Gd, and Tb)

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 ＜r_4f＞ 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.     

化合物YCo12-xTix和YFe12-xTix的结构与磁性

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.     

(Nd1-xErx)3Fe273Ti17化合物的结构与磁性

通过x射线衍射分析和磁性测量对(Nd1-xErx)3Fe273Ti17化合物的结构与磁性进行了研究.单相(Nd1-xErx)3Fe273Ti17化合物的成相范围为x=00—05之间，所有化合物均属于单斜晶系、Nd3(Fe,Ti)29型结构和A2/m空间群.着Er含量的增加，(Nd1-xErx)3Fe273Ti17化合物的晶胞体积、居里温度TC和5K下的饱和磁化强度Ms均单调减小，而5K下的饱和磁化强度Ms和Er含量的关系与稀释模型所描述的结果相一致.(Nd1-xErx)3Fe273Ti1 关键词： (Nd1-xErx)3Fe273Ti17化合物 磁晶各向异性 自旋重取向 磁相图