Electronic structure and magnetism of R(Fe,Si)12 (R = Y, Nd)

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.     

Ho2Fe17Cx的结构与磁性

用快速急冷方法制备了Ho₂Fe₁₇C_x化合物,研究了它们的形成、结构与磁性。这些化合物在高温下是稳定的,随C含量的增加,晶体结构由六角Th₂Ni₁₇型转变为菱形Th₂Zn₁₇型。测量了Ho₂Fe₁₇C_x化合物在1.5K和室温下的饱和磁化强度,得到每个Fe原子磁矩近似与C含量无关。C原子的引 关键词：     

Magnetic properties of RE0.7Ca0.3Mn0.95Fe0.05O3 (RE=Sm and Gd) manganites at low temperature

The magnetic properties of RE_0.7Ca_0.3Mn_0.95Fe_0.05O₃ perovskite with rare-earth cations (RE=Sm and Gd) were investigated by means of X-ray diffraction, Mössbauer spectroscopy, and low temperature (4.2-266 K) magnetization measurements. Structural characterization of these compounds shows that they both have orthorhombic (Pbnm) structure. The Mössbauer spectra show clear evidence of local structural distortion of the Mn(Fe)O₆ octahedron, which is based on the non-zero nuclear quadrupole interactions for high-spin Fe³⁺ ions. It was found that the local structural distortion increases significantly when Sm³⁺ is replaced by Gd³⁺. This distortion is attributed to the Jahn-Teller coupling strength as estimated from the Mössbauer effect results. The magnetic results indicate that the Curie temperature decreases as a result of replacing Sm by Gd. This is due to the decrease of the average A-site cationic radius 〈r_A〉. The rapid increase of magnetization at low temperature indicates the magnetic ordering of rare earth ions at the A-site.     

Coexistence of paramagnetism and ferromagnetism in Fe-TiO2 nanoparticle

Magnetic properties of pure and Fe doped rutile TiO₂ and TiO_2-ε are investigated using the first principle density functional theory. The results show that the considered systems are ferromagnetic. Furthermore, the origin of ferromagnetism is discussed and it is found that the double exchange and super-exchange are the main interactions in these compounds. Based on the calculations, the magnitude of the magnetic moment depends on the concentration of impurities and oxygen vacancies and the largest magnetic moment corresponds to the Fe_xTi_1-xO_2-ε. Moreover, using a model based on the bound magnetic polarons, the coexistence of ferromagnetic and paramagnetic phases can occur in Fe_xTi_1-xO₂ containing different impurity ions such as Fe⁺² and Fe⁺³ with different Curie temperatures. The finding may presents the potential application of the considered system as diluted magnetic semiconductor.     

R2Fe17C化合物的结构与内禀磁性的研究

本文系统研究了R₂Fe₁₇C(R=Y.Sm,Gd,Tb.Dy,Er)化合物的结构与内禀磁性,并与相应的R₂Fe₁₇化合物进行了比较。R₂Fe₁₇C的居里温度比相应R₂Fe₁₇的居里温度增加大约200K。本文讨论了C原子对该化合物结构与磁性的影响,同时,还对Sm₂(Fe_1-xCo_{x 关键词：}     

Magnetocaloric effect in R2Fe17 (R=Sm,Gd, Tb,Dy, Er)

A series of R₂Fe₁₇ (R=Sm, Gd, Tb, Dy, Er) have been synthesized. The magnetocaloric effect (MCE) of these compounds has been investigated by means of magnetic measurements in the vicinity of their Curie temperature. The Curie temperature of Er₂Fe₁₇ is 294 K. The maximum magnetic entropy change of Er₂Fe₁₇ under 5 T magnetic field is ∼3.68 J/kg K. In the R₂Fe₁₇ (R=Sm, Gd, Tb, Dy, Er) system, the maximum magnetic entropy change under 1.5 T magnetic field is 1.72, 0.89, 1.32, 1.59, 1.68 J/kg K corresponding to their Curie temperature (400, 472, 415, 364, 294 K), respectively.     

Structural and magnetic properties of hydrides R3Fe29−xVxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R₃Fe_29−xV_xH_y (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants , and c and the unit cell volume of R₃Fe_29−xV_xH_y decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce₃Fe_27.5V_1.5H_6.5, like Ce₃Fe_27.5V_1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce₃Fe_27.5V_1.5 and Gd₃Fe_28.4V_0.6 show the larger storage of hydrogen with y=6.5 and 6.9 in these hydrides.     

Improved magnetic properties by treatment of iron-based rare earth intermetallic compounds in anmonia

The R₂Fe₁₇ and R₂Fe₁₇C intermetallic compounds are found to absorb approximately two atoms of nitrogen per formula unit on heating in ammonia or nitrogen. The interstitial nitrides retain the original Th₂Ni₁₇ or Th₂Zn₁₇ structures, but with a large increase in unit cell volume (≈ = 7%). Curie temperatures of 420 °C are found when R = Y and 470 °C when R = Sm. There are also substantial increases in magnetisation and anisotropy field (when R = Sm). These new interstitia nitrides have excellent intrinsic magnetic properties for permanent magnet applications.     

稀土金属间化合物RFe2Zn20-xInx的结构属性研究

RFe₂Zn₂₀（R代表稀土元素）型稀土金属间化合物因其低稀土含量和良好的铁磁性,已成为铁磁材料的研究热点之一.添加第四组元对该系列化合物的晶体结构和材料性能会产生一定影响.利用晶格反演方法获得了一系列有效的原子间相互作用势,对三元RFe₂Zn₂₀和四元RFe₂Zn_20-xIn_x化合物进行原子级模拟计算.研究表明,随着稀土元素原子量的增加,三元体系的晶格参数和体积呈线性下降,第四组元引入与否对该线性关系无直接影响.第四组元In替代Zn时,择优占据16c晶位,占满16c后选择占据96g晶位,始终不占据48f晶位.择优占位的结论符合实验观测,并与晶格反演势分析的结果一致. 关键词： 原子间相互作用势 择优占位 晶体结构     

Coexistence of paramagnetism and ferromagnetism in Fe-TiO2 nanoparticle

Magnetic properties of pure and Fe doped rutile TiO₂ and TiO_2-ε are investigated using the first principle density functional theory. The results show that the considered systems are ferromagnetic. Furthermore, the origin of ferromagnetism is discussed and it is found that the double exchange and super-exchange are the main interactions in these compounds. Based on the calculations, the magnitude of the magnetic moment depends on the concentration of impurities and oxygen vacancies and the largest magnetic moment corresponds to the Fe_xTi_1?xO_2?ε. Moreover, using a model based on the bound magnetic polarons, the coexistence of ferromagnetic and paramagnetic phases can occur in Fe_xTi_1?xO₂ containing different impurity ions such as Fe⁺² and Fe⁺³ with different Curie temperatures. The finding may presents the potential application of the considered system as diluted magnetic semiconductor.     

Hydrogenation, structure and magnetic properties of La(Fe0.91Si0.09)13 hydrides and deuterides

Hydrogenation, crystal structure and magnetic properties of La(Fe0.91Si0.09)13H(D)y have been studied by pressure-composition isotherms (PCI), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and magnetization measurements. The maximum absorption capacity is found to be 1.9 H(D) atoms per formula unit as a solid solution. All hydrides and deuterides crystallize in the NaZn13-type cubic structure with the lattice parameter increasing linearly with H(D) concentration. The H(D) absorption enhances the Curie temperature significantly. The magnetic entropy change of the highly H-absorbed compound La(Fe0.91Si0.09)13H1.81 reaches ～26 J/kg·K under a magnetic field change of 5 T near the Curie temperature TC = 350 K. No observable isotope effect seems to imply that only the magnetovolume effect is responsible for the strong interplay between magnetism and lattice.     

Enhancement of magnetocaloric effects in La0.8R0.2(Fe0.919Co0.081)11.7 Al1.3 (R=Pr, Nd) compounds

The magnetic properties and magnetocaloric effects (MCEs) in La_0.8R_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 (R=Pr, Nd) compounds have been investigated. When Pr and Nd substitute for La, the Curie temperature of compounds decreases. The values of the MCEs are enhanced significantly by a partial substitution of Nd for La. Under the field change of 2 and 5 T, the maximum magnetic entropy changes for La_0.8Nd_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 compound are −4.56 and −9.46 J/Kg K, respectively. It can be exploited for room temperature magnetic refrigeration material.     

电弧炉制备的Sm2Fe17-xCrx化合物的结构与磁性

通过X射线衍射、磁测量等手段对电弧炉制备的不同热处理条件的Sm₂Fe_17-xCr_x（x=1—3）化合物的结构和磁性进行了研究.结果表明1050 ℃下退火5 d的Sm₂Fe_17-xCr_x（x=1—3）化合物具有菱方相的Th₂Zn₁₇型结构,同样温度下退 关键词： 2Fe_17-xCr_x化合物')" href="#">Sm₂Fe_17-xCr_x化合物 磁体积效应 居里温度 磁晶各向异性     

Structural and magnetic properties of Pr3(Fe1−xCox)27.5Ti1.5 (x=0.0, 0.1, 0.2, 0.3)

A novel class of Co-substituted 3 : 29 materials, Pr₃(Fe_1−xCo_x)_27.5Ti_1.5 (x=0, 0.1, 0.2, 0.3) have been synthesized. Rietveld analysis of X-ray powder diffraction patterns for the x=0, 0.1 and 0.2 compositions showed that nearly all of the compounds are formed in monoclinic symmetry, with A2/m space group with traces of α-Fe, whereas, in x=0.3, additional traces of a (Co/Fe)–Ti (1 : 12) phase are also seen. The saturation magnetization increases with Co concentration both at 5 and 300 K and is explained on the basis of a rigid band model. A magnetic transition is observed for x=0.1 near 240 K. A large increase in Curie temperature, of about 180 K for x=0.1 and about 110 K for the other concentrations, is discussed on the basis of the strengthening of TM–TM exchange by the preferential occupation of Co in some of the Fe sites originally participating in antiferromagnetic bonds.     

赝二元化合物Dy(Fe0.9M0.1)2(M=B,Al,Ga)的磁性研究

研究了赝二元化合物Dy(Fe_0.9M_0.1)₂(M=B,Al,Ga)的磁性。M对Fe的置换,使居里温度下降,Fe原子的磁矩改变。矫顽力随温度的降低,增加很快,增加的幅度与M有关。磁化强度的温度关系,在磁场小于临界值时,出现反常和热磁效应。用Fe原子局域环境的变迁和低温下内禀磁硬度的急剧增加,解释了上述现象。 关键词：     

Crystal structure and magnetic properties of Nd（Mn1-xFex）2Si2 compounds

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.     

Crystallographic and magnetic properties of (Nd,Dy)3Fe27.5(Ti,Mo)1.5 compounds

A systematic study of the formation, structure and magnetic properties of (Nd,Dy)₃Fe_27.5(Ti,Mo)_1.5 compounds has been performed. Rietveld analyses of the X-ray patterns of the samples indicate that the concentrations of Ti and Mo affect the formation and structural properties slightly, whereas different rare-earth (Nd and Dy) contents influence them significantly. It is found that high Dy contents make it difficult to form the 3:29-type structures. The Curie temperatures of Nd_2.1Dy_0.9Fe_27.5Ti_1.5−xMo_x decrease monotonically as more Ti was replaced by Mo but their saturation magnetizations remain almost unchanged; in contrast, for Nd_3−yDy_yFe_27.5TiMo_0.5, their saturation magnetizations decrease monotonically with increasing Dy contents while their Curie temperatures are constant.     

STRUCTURE AND MAGNETIC PROPERTIES OF NITRIDES R3Fe29-xCrxN4

A systematic investigation of nitrides R₃Fe_29-xCr_xN₄(R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. The nitrogen concentration in the nitride R₃Fe_29-xCr_xN_y was determined to be y=4. Nitrogenation leads to a relative volume expansion of about 5.3%. The lattice constants and unit cell volume decrease with in creasing rare earth atomic number from Nd to Dy, reflecting the lanthanide contraction. In average, the increase of Curie temperature upon nitrogenation is about 200 K, compared with its parent compound. The nitrogenation also results in a remarkable improvement in the saturation magnetization and anisotropy fields for R₃Fe_29-xCr_xN₄ at 4.2 K and room temperature, comp ared with their parent compounds. A spin reorientation of Nd₃Fe_24.5 Cr_4.5N₄ occurs at around 368 K, which is 138 K higher than that of Nd₃Fe_24.5Cr_4.5.Magnetohistory effects of R₃Fe_29-xCr_xN₄(R=Nd and Sm) are observed in a low field of 0.04 T. First order magneti zation process occurs in Sm₃Fe_24.0Cr_5.0N₄ in magnetic fields of around 3.0 T at 4.2 K. After nitrogenation the easy magnetization direction of Sm₃Fe_24.0Cr_5.0 is changed from the easy cone structure to the uniaxial. The excellent intrinsic magnetic properties of Sm₃Fe_24.0Cr_5.0N₄ make this compound a hopeful candidate for new high performance permanent magnets.     

Mössbauer studies of interstitial rare earth-iron intermetallics

Two series of interstitial rare earth-iron intermetallics, R₂Fe₁₇N_3-σ and R₂Fe₁₇C_3-σ have been prepared by gas phase reaction from the R₂Fe₁₇ parent compounds (R=Ce, Pr, Nd, ... Lu and Y). The interstitials raise the Curie temperature of the compounds by 390 K in the case of N and 330 K in the case of C. Mössbauer spectra at 15 K and 293 K, and data as a function of temperature for R=Er and Tm are analysed to yield hyperfine interactions at the four sites, and information on the local magnetization and its orientation. The change in hyperfine field is not proportional to the change in magnetization produced by the interstitials, being much greater in the nitrides than the carbides. Likewise for the isomer shifts. These effects are discussed in terms of the differences in electronic structure of the nitrides and carbides.     

Pressure-Induced Decrease in the Curie Temperature of Gd<Subscript>2</Subscript>Fe<Subscript>17</Subscript>: LSDA+U Calculations

To explain the magnetic properties of advanced ferromagnetic intermetallic compounds of the R₂Fe₁₇ (R is a rare-earth element) class, experimentalists often use the hypothesis of competition between ferromagnetic exchange and antiferromagnetic exchange between four types of the nearest iron atoms in nonequivalent lattice sites. For the rhombohedral Gd₂Fe₁₇ ferromagnet, we calculate the magnetic moments of iron and gadolinium ions, the parameters of exchange between Fe atoms, and Curie temperature T_C at a zero pressure and during hydrostatic lattice compression. The magnetic moment of the unit cell of Gd₂Fe₁₇ is shown to decrease under pressure, and this decrease is almost completely associated with a decrease in the magnetic moments of Fe rather than Gd ions, the pressure dependence of the magnetic moments of which is weaker by an order of magnitude. In contrast to the hypothesis regarding the competition of exchange interactions between different kinds of Fe atoms, the parameters of exchange between the nearest iron atoms in different crystallographic sites are found to be positive ferromagnetic (at a zero pressure and during compression), and a ferromagnetic character of interaction is shown to remain unchanged under pressure even for Fe atoms in the so-called dumbbell sites with the nearest interatomic distances. The Curie temperature T_C of Gd₂Fe₁₇ is shown to decrease with increasing pressure. The changes in the exchange parameters and the magnetic moments of Gd₂Fe₁₇ during compression are found to be mainly related to a change in the position of energy spectrum branches with respect to each other and the Fermi level ?_F rather than to a change in the overlapping of wavefunctions, which play a minor role.