新型金属间化合物Sm(TiFe)12的结构与磁性

SmTiFe_x(x的数值为8—11)可形成稳定的金属间化合物,经测定,晶体结构属于ThMn₁₂型四方结构,空间群为14/mmm,本文着重分析了Sm(TiFe)₁₂和Gd(TiFe)₁₂的结构和磁性。Sm(TiFe)₁₂具有很强的单轴磁晶各向异性,易磁化方向为c轴,居里温度610K。通过对Gd(TiFe)₁₂磁性的研究,进一步分析了在Sm(TiFe)₁₂中Sm和Fe次晶格的各向异性,实验结果表明,Sm和Fe次晶格都具有单轴磁晶各向异性,易磁化方向皆沿c轴。这是继Nd₂Fe₁₄B型永磁体以后发现的又一种具有单轴磁晶各向异性的三元稀土-铁金属间化合物。 关键词：     

YBa2(Cu0.95M0.05)3O7-δ的代换效应及其中子衍射研究

X射线衍射实验表明YBa₂(Cu_0.95M_0.05)₃O_7-δ(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu和Zn)均为单相结构。Fe,Co,Ni和Zn对Cu的替代使超导临界温度T_c显著下降,而同样含量的Ti,V,Cr,Mn对Cu的替代并未对超导性能产生显著影响。并利用中子衍射分析了Ti,Mn,Fe和Co对Cu原子的取代,发现代换原子对Cu的两个晶位各自存在不同的择优占据 关键词：     

Er3(Fe,Co, M)29化合物(M=Cr,V, Ti,Mn, Ga,Nb)的结构与磁性

合成了Er_３Fe_29-x-yCo_xM_y化合物(M=Cr, V, Ti, Mn, Ga, Nb )并用x射线衍射和磁测量等手段研究了它们的结构和磁性. 发现Fe基Er_３(Fe,M)_２９化合物结晶成哑铃对Fe-Fe无序替代的Th₂Ni₁₇型结构(P6₃/mmc空间群)而不能形成Nd₃(Fe,Ti)_２９型结构，因此其化学式也可以用Er_2－n(Fe,M)_17+2n (n=0.2)表示. 当Er_３Fe₂₉化合物中部分Fe原子被M原子所取代时，其居里温度均有一定程度的提高. 所有Er_３(Fe,M)_２９化合物在室温均为易面型各向异性. 当Er_３(Fe,M)_２９ (M=Cr, V)中的部分Fe原子被Co原子取代且Co原子数与Fe原子数达到一定比值时，得到一个单斜结构的新相. 磁测量表明Er_３Fe_19.5Co₆V_3.5在室温可能为单轴各向异性，在162K出现自旋重取向，其各向异性由易轴型变为易面型. 在5K下于难磁化方向磁化时观察到一个一级磁化过程(FOMP). 关键词： 稀土金属间化合物 晶体结构 磁晶各向异性     

Y(Mn1-xCox)12的中子衍射研究

Y(Mn_1-xCo_x)₁₂属于ThMn₁₂型四角体心结构,空间群为14/mmm,z=2。用粉末中子衍射测定了Co,Mn原子在8i,8j和8f晶位上的有序度。结构分析表明:Go优先占据8f晶位,其次占据8j晶位;在x<0.67时,几乎不进入8i晶位。最后,对实验结果作了讨论和推断。 关键词：     

(Nd1－xGdx)3Fe27.31Ti1.69化合物的结构和磁性

通过X射线衍射和磁性测量等手段研究了(Nd_1-xGd_x)₃Fe_27.31Ti_1.69(0≤x≤0.6)化合物的结构和磁性.X射线衍射测量结果表明Gd替代后并未改变Nd₃(Fe,Ti)₂₉化合物的晶体结构，但引起了晶胞体积收缩.随着Gd含量的增加，化合物的居里温度T_C和室温磁晶各向异性场B_a单调增加，而自旋重取向 关键词： 1-xGd_x)₃Fe_27.31Ti_1.69化合物')" href="#">(Nd_1-xGd_x)₃Fe_27.31Ti_1.69化合物 磁晶各向异性 自旋重取向 磁相图     

R(Fe，Mo)12型稀土永磁材料热膨胀反常现象研究

采用x射线粉末衍射方法测量了不同温度下R(Fe，Mo)₁₂化合物(R=Nd，Y，D y)的晶格常数，对沿不同轴向的热膨胀反常程度进行了计算.分析认为R(Fe，Mo)_{12化合物热膨胀反常主要取决于Fe-Fe相互作用，根据Nd(Fe，Mo)12的结构参 数，不仅较短的Fe-Fe键负相互作用对热膨胀反常有贡献，8j-8j等较强的Fe-Fe正相互作用 也有很大贡献.另外还讨论了第三元素Mo的替代作用影响热膨胀反常的机理. 关键词： x射线衍射 R(Fe 12}化合物')" href="#">Mo)₁₂化合物 热膨胀反常     

3∶29型Gd3(Fe1-xCox)29-yCry化合物的成相与结构

通过X射线衍射分析和磁测量研究了Gd-Fe-Co-Cr四元系中对应于化学式Gd₃(Fe,Co,Cr)₂₉且Gd含量为一定值的截面内富Fe,Co区的相关系,重点探索了高Co含量3∶29型化合物合成的可能性,研究了3∶29型Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的结构与磁性.研究结果表明,获得3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的范围为:y=5,0≤x≤0.7;y=5.5,0.7≤x≤0.8和y=6,0.8≤x≤0.9.基于对Gd₃(Fe_1-xCo_x)_29-yCr_y化合物成相条件的研究,成功地合成了纯Co基Gd₃Co_29-yCr_y化合物,其固溶范围为6.5≤y≤7.3.3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的晶体结构都属于单斜晶系,Nd₃(Fe,Ti)₂₉型结构,空间群为A2m.得到3∶29型单相Gd₃(Fe_1-xCo_x)_29-yCr_y化合物的固溶极限即Co含量的极大值与稳定元素Cr含量有关.Co原子的含量越高,所需稳定元素Cr的含量越大.值得注意的是,用Co原子替代Fe原子会导致Gd₃(Fe_1-xCo_x)_29-yCr_y化合物磁晶各向异性的显著改变.当x≥0.4时,化合物的磁晶各向异性从易面型转变为易轴型 关键词： 3(Fe_1-xCo_x)_29-yCr_y化合物')" href="#">Gd₃(Fe_1-xCo_x)_29-yCr_y化合物 相关系和相结构 X射线衍射 磁晶各向异性     

R3(Fe,Mo)29Nx的晶体学特性和内禀磁性

研究了R₃(Fe,Mo)₂₉(R=Ce,Nd,Sm,Gd,Tb,Dy,Y)氮化物的晶体学特性和内禀磁性.主要研究内容为：氮化对R₃(Fe,Mo)₂₉金属间化合物的点阵参数、居里温度T_C、饱和磁化强度σ_s和各向异性场B_a的影响. 关键词：     

熔体快淬Pr(Fe1-xCox)2合金的结构和磁性

通过熔体快淬方法获得Pr(Fe_1-xCo_x)₂合金条带,经过X射线衍射、差示扫描量热计和磁性测量对其结构、磁性和热稳定性进行了研究.发现当Co的含量x大于0.2时才可能获得Pr(Fe,Co)₂立方Laves相化合物.对Pr(Fe_0.6Co_0.4)₂合金,在快淬速度为30m/s时,条带由Pr₂(Fe,Co)₁₇,Pr(Fe,Co)₂和富稀土相组成;在速度为40m/s时,获得了几乎单相的Pr(Fe_0.6Co_0.4)₂化合物,其居里温度为305℃;在速度为45m/s时,除了Pr(Fe_0.6Co_0.4)₂化合物外,还存在少量的非晶相.Pr(Fe_0.6Co_0.4)₂化合物在770℃以上发生分解.用40m/s快淬纳米晶粉胶粘磁体有大的磁致伸缩系数（λ_∥-λ_⊥=140×10^-6)和高的硬磁性能（_iH_c=398kA/m). 关键词：     

Fe(NH2trz)3·(BF4)2掺杂聚芴的有机电致发光器件

对于RGB有机电致发光器件(OLEDs),蓝光非常重要.在现有各种蓝光材料中,聚芴(PFO)非常稳定且荧光量子效率可达80%,但它有一个非常大的缺点:电致发光会产生异常绿光带.这严重影响了PFO相关器件的饱和色纯度.本文使用分子基磁性材料Fe(NH₂trz)₃·(BF₄)₂掺杂PFO方法,解决了这一难题.以ITO为衬底,制作了结构为ITO/PEDOT:PSS/PFO:Fe(NH₂trz)₃·(BF₄)₂/CsCl/Al的器件.报道了利用Fe(NH₂trz)₃·(BF₄)₂特殊的电子自旋态调制PFO的光电特性,实现了PFO的强烈纯正蓝光发射.详细研究了Fe(NH₂trz)₃·(BF₄)₂对PFO光电特性的影响.在4 V至9 V电压的偏置下,没有Fe(NH₂trz)₃·(BF₄)₂的器件,发出特别异常的绿光.然而,与此形成明显对照的是:Fe(NH₂trz)₃·(BF₄)₂掺杂的器件发出强烈的本征蓝光;PFO绿色发光带被成功压制;随着电压的变化,器件光谱的蓝光部分在整个EL谱所占比例没有改变.运用光电磁一体化测量技术,进一步研究了PFO掺杂Fe(NH₂trz)₃·(BF₄)₂器件的磁发光(MEL)和磁电导(MC)效应.发现PFO:Fe(NH₂trz)₃·(BF₄)₂和纯PFO薄膜内都没有激基缔合物产生.运用发光动力学理论,分析了Fe(NH₂trz)₃·(BF₄)₂阻断PFO异常绿光发射的机理.     

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.     

An57Fe Mössbauer study of rare-earth intermetallic compounds R(Fe11Ti)

⁵⁷Fe Mössbauer spectra are reported for the ThMn₁₂ structure series of intermetallic compounds R(Fe₁₁Ti) (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu). The Mössbauer spectroscopy of oriented absorbers has been used to study the spin reorientation transitions exhibited by the members of the series where the second-order Stevens coefficient α_J of the rare-earth (Nd, Tb and Dy) is negative. A simple model has been established to deduce the canting angle from the Mössbauer spectra of oriented absorbers. The results are analyzed in terms of a crystal-field model. The crystal field parameters must be increased significantly to account for the observed large anisotropy in the Sm(Fe₁₁Ti) compound, which may find applications as a permanent magnet.     

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 RFe10M2 (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.     

Phase stability and site preference of Sm(Fe,T)12

The structure of intermetallics Sm(Fe,T)₁₂ is analyzed via a quasi-ab initio pair potentials Φ_Fe–Fe(r), Φ_Sm–Fe(r), Φ_Sm–Sm(r), Φ_Sm–T(r), Φ_Fe–T(r) and Φ_T–T(r). The calculation results show that each of Cr, V, Mo and Ti significantly decreases the cohesive energy of Sm(Fe,T)₁₂, and thus stabilizes its structure of ThMn₁₂. The calculated lattice constants coincide quite well with experimental values. The sequence of site preference occupation is 8i, 8j and 8f, with the 8i occupation corresponding to the greatest energy decrease. The calculated results also show that each of Co, Cu, Ni and Sc does not stabilize the system with the structure of ThMn₁₂. The calculated crystal structure can recover after either an overall wide-range macro-deformation or atomic random motion, demonstrating that an Sm–Fe–T system has the stable structure of ThMn₁₂. The crystal space group remaining consistent at different temperatures is also shown in this paper. All of the results verify that the first principle potentials based on the lattice inversion technique are effective.     

X-ray photoelectron spectroscopy of LiM0.05Mn1.95O4 (M = Ni,Fe and Ti)

LiMn₂O₄ and LiM_0.05Mn_1.95O₄ (M = Ni, Fe and Ti) were synthesized by using solid-state reactions and their surface stoichiometries were confirmed by XPS data. The crystal and electronic structures were investigated by using X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). XRD data suggested that LiM_0.05Mn_1.95O₄ possesses nearly no any variations in lattice parameters compared with LiMn₂O₄ for slight substitution of Ni, Fe and Ti; the substituted Ni, Fe and Ti ions were located on the 16d octahedral sites in the spinel crystal lattice. The XPS results suggested that Fe and Ti ions were at + 3 and + 4 oxidation states, respectively; while Ni ions are mixed with + 2 and + 3 oxidation states. The normal oxidation state of Mn ions in the above four materials is almost the same and calculated as + 3.55 according to the splitting energies of Mn3s states.     

Conversion electron Mössbauer spectroscopic study of YIG substituted with Bi,Ti, Ga and La

YIG films, substituted with Bi, Ti, Ga and La, were grown on a (111) plane of Gd₃Ga₅O₁₂ or (Gd, Ca)₃(Ga, Mg, Zr)₅O₁₂ by a liquid phase epitaxial method. With the increase of the concentration of Bi atoms, which are substituted at 24c sites of YIG, the magnetic hyperfine fields at 16a and 24d Fe sites increased and the direction of magnetic moments changed from parallel to 45° to the (111) plane. With the increase of Ga concentration, the hyperfine fields at 16a and 24d Fe sites decreased. The hyperfine interaction and the substitution effect of YIG films are discussed.     

Mössbauer spectroscopy of R2Fe14B and related compounds

The Mössbauer Spectroscopy (MBS) has been widely used in the last 4 years for the study of the recently discovered ternary compounds R₂Fe₁₄B where R means Y, Th or a rare earth element. The strong interest for this class of intermetallics arose drastically after the discovery of the exceptional properties of Nd₂Fe₁₄ as an ideal material for permanent magnet applications. The newest results about hyperfine fields B_HF, quadrupole splitting E_Q and isomer shifts I.S. at the 6 crystallographically different Fe sites and at the 2 R sites in the R₂Fe₁₄B and their impact on the understanding of the local magnetic moments and magnetocrystalline anisotropy will be reviewed. In the case of RFe_12?xM_x compounds where M=V, Ti, Si, Mo, W, Cr, complex Mössbauer spectra were obtained because of the presence of 3 crystallographically inequivalent Fe sites and the presence of differents amounts of the M component on one or more of these sites.