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基于第一性原理投影缀加波和梯度矫正局域密度近似(PAW-GGA), 研究了Nd2Fe14B和Dy2Fe14B的基态晶格属性, 进而对Dy在Nd2Fe14B晶格中的掺杂进行了研究, 并采用GGA+U的方式进行了原子磁矩计算, 并与自旋轨道耦合 (SOI) 计算结果进行了对照. 置换计算表明, Dy原子倾向于置换Nd2Fe14B晶格中4f位的稀土原子. 磁矩计算表明, 在R2Fe14B (R: 稀土元素) 晶格中, 4f位的稀土元素与Fe原子作用更强, 对磁性能的影响更大. 稀土原子与Fe的作用与距离呈正相关.
关键词:
2Fe14B')" href="#">Nd2Fe14B
晶格占位
形成能
原子磁矩 相似文献
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本文对Nd-Fe-Si三元系富铁区域相的结构和磁性进行了研究。结果表明,Nd-Fe-Si三元系富铁区域(Fe>40at%),除出现NdFe2Si2三元金属间化合物外(Si>20at%),同时只出现Nd2(Fe,Si)17赝二元金属间化合物,其中Si取代9d位的Fe原子,而不能形成类似于Nd2Fe14B的三元金属间化合物,Si取代Nd2Fe17中的9d位Fe原子后,使晶胞体积缩小;使饱和磁化强度减小;同时使Fe次晶格的铁磁相互作用增强,导致居里温度增高;还使得Fe次晶格的易面各向异性减弱,造成室温下各向异性场减小。
关键词: 相似文献
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利用非自耗真空电弧熔炼法制备了NdNi2Ge2化合物样品,采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其晶体结构. 结果显示该化合物的空间群为I4/mmm,点阵参数为:a=4.120(1),c=9.835(0),Z=2,Nd原子占据2a晶位,Ni原子占据4d晶位,Ge原子占据4e晶位. NdNi2Ge2化合物呈现顺磁性,应用居里-外斯定律拟合计算得到居里-外斯常数为25.8,居里-外斯温度为6.24 K. 有效势磁矩为3.69μB,这与理论计算Nd3+的磁矩相符,表明磁矩主要源于Nd3+. 电阻率变化范围为0.3 Ω ·μm-1-1 Ω ·μm,电阻曲线拟合显示NdNi2Ge2呈半金属性.
关键词:
2Ge2')" href="#">NdNi2Ge2
Rietveld结构精修
电磁输运 相似文献
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Nd2Fe14B是一种磁能积很高的优良的永磁材料,但在实用上稍嫌它的居里温度低了一点。为了提高它的居里温度,人们曾用某些元素替代其中的一些铁作了尝试。文献[9]及我们最近的实验表明:用硅代替部分铁之后,材料的居里点都获得了提高。本文用中子衍射法研究了Si在Y2Fe14B中的占位情况,以了解Si对磁性能产生的影响。中子衍射的结果表明:Si择优地占据c,j1及k2晶位。最后,用磁交换作用对结果进行了讨论。
关键词: 相似文献
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YuQi YangT. Wang G.N. Li Q. HuangQ.Q. Gao J.B. LiG.Y. Liu J. LuoG.H. Rao 《Physica B: Condensed Matter》2011,406(10):1995-1999
The crystal and magnetic structures of the composite compound Nd2Co6Fe have been investigated by high-resolution neutron powder diffraction and X-ray powder diffraction. The compound crystallizes in the hexagonal Ce2Ni7-type structure consisting of Nd(Co,Fe)2 and Nd(Co,Fe)5 structural blocks alternately stacked along the c-axis. Multi-pattern Rietveld refinement of neutron diffraction and X-ray diffraction data at room temperature reveal that substitution of Fe for Co occurs exclusively in the Nd(Co,Fe)5 structural blocks. The preferential occupation of the Fe atoms in the structure is discussed based on the mixing enthalpy between Nd and Fe atoms and on the lattice distortions. In agreement with the reported magnetic phase diagram of the Nd2Co7−xFex compounds, magnetic structure models with the moments of all atoms in the ab plane at 300 K and along the c-axis at 450 K provide a satisfactory fitting to the experimental neutron diffraction data. The refinement results show that the atomic moments of (Co,Fe) atoms within the Nd(Co,Fe)5 blocks decrease slightly with temperature, whereas the atomic moments of Nd in the compound and of (Co,Fe) atoms at the interface between the Nd(Co,Fe)2 and Nd(Co,Fe)5 blocks are reduced significantly. 相似文献
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Yilong Ma Dengming ChenAnruo Zhou Jianchun SunPengjun Cao 《Physica B: Condensed Matter》2012,407(23):4562-4566
It is difficult to obtain the crystallographic alignment for stoichiometric Nd2Fe14B alloys by applying the melt-spun and subsequent hot-pressing and hot-deformation techniques. However, the enhanced alignment and magnetic properties of die-upset nano-crystal Nd2Fe14B magnets have been obtained by Nb addition in the present paper. The magnetic properties studies show that Nb addition leads to the remarkable increase of remanence Br and intrinsic coercivity Hci, which is due to the improvement of c-axis texture and refinement of microstructure. Microstructure studies using transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that Nb atoms are enriched at grain boundary and the NbFeB phase is observed with increasing Nb content. Since some Fe atoms in the Nd2Fe14B phase participate in the formation of NbFeB phase, the excessive Nd atoms may be enriched at grain boundary, which may improve the physical property of grain boundary and provide a mass transport pass for preferential growth of oriented Nd2Fe14B grains, thus leading to the enhanced alignment and magnetic properties. 相似文献
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The crystallographic and the magnetic structures of the composite compound Nd2Co7 at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce2Ni7-type structure and consists of alternately stacking MgZn2-type NdCo2 and CaCu5-type NdCo5 structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μB-1.1 μB and the atomic moment of Nd in the NdCo5 slab is close to the theoretical moment of a free trivalent Nd3+ ion, whereas the atomic moment of Nd in the NdCo2 slab is much smaller than the theoretical value for a free Nd3+ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo2 and NdCo5 compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd2Co7 compound. 相似文献
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The magnetic properties of Nd4.5Fe77−xMnxB18.5 (x=0, 1 and 2) nanocomposites prepared by the crystallization of amorphous precursors were investigated. Addition of Mn is found to decrease the crystallization temperature of the amorphous ribbons. The intrinsic coercivity iHc and maximum energy product (BH)max increase from 2.6 kOe and 9.1 MGOe for x=0 to 3.1 kOe and 10.3 MGOe for x=1, respectively, and the remanence ratio Mr/Ms increases from 0.70 to 0.72. The effect of Mn on Curie temperature TC and the thermal stability of Mr and iHc were also studied. 57Fe Mössbauer spectra have been recorded for x=0, 1 and 2 ribbons at room temperature and site preference of the Mn atoms in Fe3B and Nd2Fe14B phases is discussed using the Mössbauer spectroscopy. 相似文献
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The newly developed full-potential linearized augmented plane wave (LAPW) and local orbitals (lo) based on standard APW methods
are briefly introduced, and the structure and magnetic properties of R(Fe, Si)12 compounds (R = Y, Nd) are calculated using the method. The distribution of Si at different sites is analyzed based on total energy of
one crystal unit with structure having been optimized. The characters of magnetic moments, total density of states (TDOS)
and partial density of states (PDOS) for different crystal sites Si occupies are obtained and analyzed. The results show that
the total magnetic moments of RFe10Si2 (R = Y, Nd) are larger than those of RFe10
M
2 (M = Ti, V, Cr, Mn, Mo and W) and the hybridization mechanism is seen as follows. Si(8j) reduce the magnetic moments of Fe at
three sites, however, Si(8f) mainly reduce the magnetic moments of Fe(8i) and Fe(8j) atoms. The Curie temperature is markedly
enhanced by the introduction of Si atoms according to spin fluctuation of DOS at Fermi level. 相似文献
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X-ray powder diffraction,resistivity and magnetization studies have been performed on polycrystalline Nd(FexMn1-x)2Si2 (0 ≤ x ≤ 1) compounds which crystallize in a ThCr2Si2-type structure with the space group I4/mmm.The field-cooled temperature dependence of the magnetization curves shows that,at low temperatures,NdFe2Si2 is antiferromagnetic,while the other compounds show ferromagnetic behaviour.The substitution of Fe for Mn leads to a decrease in lattice parameters a,c and unit-cell volume V .The Curie temperature of the compounds first increases,reaches a maximum around x = 0.7,then decreases with Fe content.However,the saturation magnetization decreases monotonically with increasing Fe content.This Fe concentration dependent magnetization of Nd(FexMn1-x)2Si2 compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe.The temperature’s square dependence on electrical resistivity indicates that the curve of Nd(Fe0.6Mn0.4)2Si2 has a quasi-linear character above its Curie temperature,which is typical of simple metals. 相似文献
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The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules.
The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic
structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional
to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between
magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the
number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed
in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting
point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic
and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the
electrons obviously affect the physical properties.
Supported by the National High Technology Development Program of China (Grant No. 2007AA03Z458) 相似文献
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Jingzhi Han Changsheng WangHonglin Du Haiying ChenYingchang Yang 《Journal of magnetism and magnetic materials》2008
Effects of such additives as Co, Zr, Nb or Ga on hydrogen absorption and desorption characteristics of Nd(Fe,Mo)12 alloys are investigated. It is found that Zr or Nb addition increases the disproportionation temperature of Nd(Fe,Mo)12 alloys, and Co or Ga addition decreases the recombined temperature of its disproportionated products. This shows that Zr or Nb addition retards the disproportionation, while Co or Ga addition is effective for improving the recombination, which is similar to the effects of the additives on the hydrogen absorption and desorption characteristics of Nd2Fe14B alloys. However, according to X-ray diffraction (XRD) investigations for the magnetic-oriented samples, the final hydrogenation disproportiontation desorption recombination (HDDR) NdFe10.5−XMXMo1.5 (M=Co, Zr, Nb or Ga) products are isotropic. The effects of additives on hydrogen absorption and desorption characteristics of Nd2Fe14B and Nd(Fe,Mo)12 alloys are very similar, but the magnetic anisotropy of the final two HDDR products are different. In order to investigate this, similarities and differences of the two alloy systems and their corresponding HDDR phenomena are further studied. The results show that the formation of anisotropic powders may be related to the disproportionated products and crystal growth direction of the Nd2Fe14B and Nd(Fe,Mo)12 system. 相似文献
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The influences of boron addition on the phase formation, Curie temperature and magnetic entropy change of the NaZn13-type La(Fe0.9Si0.1)13 compound have been investigated. Eight boron containing La(Fe0.9Si0.1)13Bx samples were prepared with x=0, 0.03, 0.06, 0.1, 0.2, 0.3, 0.5 and 0.6, respectively. Experimental results show that a small amount of B addition in La(Fe0.9Si0.1)13 forms the solid solution NaZn13-type structure phase by substituting B for Si or doping B into interstitial position of the lattice, preserves its giant magnetocaloric effects due to their first-order structural/magnetic transition, as well as increase its Curie temperature Tc slightly. The maximum magnetic entropy changes in the magnetic field change of 0–1.6 T are around 20 J kg–1 K–1 for the samples with Boron addition less than 0.3, while improving the Curie temperatures by 2 K. 相似文献