FexMn1-x合金在GaAs(001)表面外延的结构和磁性

报道了对于0≤x≤1的Fe_xMn_1-x合金在GaAs(001)表面上分子束外延的结构与磁性的实验结果,当x>0.8时,Fe_xMn_1-x合金以单晶体心立方结构生长;当x<0.35时,则以单晶面心立方结构生长;对于0.35xMn_1-x生长的结构比较复杂,而正是在这一区域中,该合金发生了从铁磁相到反铁磁相的转变. 关键词：     

Crystal structure and valence state of cerium in CePd3−xPtx alloys

Cerium is in a mixed valent state in CePd₃ (AuCu₃ type structure) while it is in a trivalent state in CePt₃ (defect C15 Laves type structure). CePd_3?xPt_x alloys have been prepared and are found to have AuCu₃ type structure for 0 ? x ? 1 and defect Laves type structure for 1.75 < x ? 3.0. From susceptibility measurements on these alloys in the temperature range 77–400 K, it is inferred that cerium is in a mixed valent state in all the AuCu₃ type alloys, but in a trivalent state in all the Laves phase type alloys in CePd_3?xPt_x series.     

组合结构化合物Ho2Ni7-xFex(x=0-3.0)的晶体结构、结构转变和磁性

在金属间化合物的结构演变中,原子尺寸因素起着重要的作用.由于密堆积效应,不同原子半径比的元素往往形成不同的结构.而自由电子填充于原子构成的晶体结构的间隙中,它对化合物的结构也有影响.基于组合结构化合物Ho2Ni7-xFex,结合原子尺寸与自由电子对晶体结构的不同影响,文章探讨一种单位体积内自由电子浓度的经验方法来判断Ho2Ni7-xFex化合物中两种异构体间的转变.随着Fe含量的增加,Ho2Ni7-xFex化合物先结晶成Gd2Co7型三方结构,然后结晶成Ce2Ni7型六方结构.利用Rietveld精修技术和磁测量,获得了化合物的晶体结构参数和饱和磁化强度.化合物晶胞常数随Fe含量增加而增加,饱和磁化强度则随之减少(dMs/dx=-2).分析结果表明,单位体积内自由电子浓度更高,化合物形成三方结构,反之则形成六方结构.     

The electronic structure of bcc-based random solid solutions of transition metals

The electronic structure of Nb _x Zr_1–x , V _x Nb_1–x and Mo _x V_1–x random solid solutions with the bcc lattice structure is investigated in the frame of the first-principles tight-binding muffin-tin orbital method and the coherent potential approximation. The total and component densities of states as well as the Bloch spectral densities are determined over a broad concentration range.     

Neutron diffraction studies of the magnetic properties of Pr0.5Sr0.5Co1 ? x Mn x O3 solid solutions

The crystal structure and magnetic properties of a system of Pr_0.5Sr_0.5Co_{1 ? x} Mn _x O₃ solid solutions were studied by neutron diffraction and magnetization measurements. It is shown that, at a low manganese concentration, the structure can be described by the I/2a monoclinic space group; with increasing substitution level x the structure becomes orthorhombic. For x > 0.9 the crystal structure is tetragonal at high temperatures and the symmetry is lowered to orthorhombic with lowering the temperature. The substitution of cobalt for manganese leads to the destruction of long-range ferromagnetic order near x ?? 0.25. A transition from the high-temperature ferromagnetic phase to the A-type low-temperature antiferromagnetic phase is observed at x ?? 0.93 in the temperature range 110?C160 K.     

Structure of the intermediate high-pressure phases of ternary lead tellurides

In chambers with diamond anvils, the structure of high-pressure phases of ternary lead tellurides Pb_1?x Sn_xTe (x = 0.29) and Pb_1?x Mn_xTe (x = 0.05) and nonstoichiometric crystals Pb_0.55Te_0.45, Pb_0.45Te_0.55 is analyzed by the synchrotron radiation diffraction method at pressures of P up to 14 GPa. The orthorhombic structure of the intermediate high-pressure phase (space group Pnma) is determined for all the samples above 6 GPa. Models of the phase transition in PbTe from the initial rock salt structure to the orthorhombic phase, which constitutes a distorted variant of NaCl, as well as the properties of this phase, are discussed.     

Ab initio calculation of Ni50−xFexTi50

The structure, lattice dynamics and electronic band structure of Ni_43.75Fe_6.25Ti₅₀ were obtained using ab initio calculations. The phonon dispersion relations and phonon density of states were calculated using the direct method. The stability of Ni_50−xFe_xTi₅₀ structure for x=0.0, 6.25, 12.5, 25 has been investigated and shown that the orthorhombic structure is the most stable phase for x=25.     

白宝石衬底上生长的MgxZn1-xO晶体薄膜的结构和光学性能

在白宝石（sapphire）衬底上低温外延生长出了Mg_xZn_1-xO晶体薄膜.x射线衍射（XRD）及能量色散x射线（EDX）分析表明，Mg_xZn_1-xO薄膜的晶体结构依赖于薄膜中Mg的组分x，随着Mg组分的增大，Mg_xZn_1-xO薄膜的结构从与ZnO晶体一致的六方结构转变为与MgO晶体一致的立方结构.对Mg_xZn_1-xO薄膜的紫外透 关键词： 电子束蒸发反应 xZn_1-xO晶体薄膜')" href="#">Mg_xZn_1-xO晶体薄膜 结构和光学性能     

(1-x)(K0.5Na0.5)NbO3-xSrTiO3陶瓷的弛豫铁电性能

通过对（1-x）（K_0.5Na_0.5）NbO₃-xSrTiO₃（0≤x≤0.15）陶瓷的相组成、晶体结构和介电性能的研究发现,该陶瓷为单一的钙钛矿结构相.当x含量较小（x＜0.1）时为正交相结构,x≥0.1时转变为四方相结构.随着SrTiO₃掺杂量的增加,样品的致密度增加,样品由正常铁电相逐渐向弥散铁电相转变,且相 关键词： 弛豫铁电体 0.5Na_0.5）NbO₃铁电陶瓷')" href="#">（K_0.5Na_0.5）NbO₃铁电陶瓷 3掺杂')" href="#">SrTiO₃掺杂 相变温度     

Mössbauer,magnetic, and x-ray properties of the system (FeS)1−x(FeSe)x

Powders of (rmFeS)_1?x(FeSe)_x have been studied by Ms?sbauer, magnetic, and X-ray techniques. For our heat treatment of the samples the structure of the solid solutions is NiAs-like for 0≤x≤0.6, beyond which the structure is PbO-like. The samples contain also increasing amounts (with increasing x) of spurious “background” material which consists of metallic iron together with commensurate amounts of Fe₇S₈ and/or Fe₇Se₈. The tetragonal (PbO-like) FeSe shows no magnetic hyperfine structure and is thought to exhibit Pauli paramagnetism.     

X-ray spectra and electronic band structure of nitrogen in Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N solid solid solutions

The electronic energy structure of the valence band and the x-ray absorption near edge structure (XANES) region of nitrogen in Al _x Ga_1?x N solid solutions and binary crystals of gallium nitride GaN and aluminum nitride AlN are calculated using the local coherent potential method and the cluster version of the muffin-tin approximation within the framework of the multiple scattering theory. It is demonstrated that the calculated electron densities of states correlate with the nitrogen K x-ray emission and nitrogen K x-ray absorption spectra. The electronic energy structure of the top of the valence band and the XANES region in Al _x Ga_1?x N solid solutions are compared with those in the binary crystals of the GaN and AlN nitrides, and an interpretation of their specific features is proposed. An analogy is drawn between the evolution of the electronic energy structure of the valence band and the XANES region in the alloys under investigation and the evolution of the electronic band structure in the Al _x B_1?x N and B _x Ga_1?x N alloys. General trends in the transformation of the structure and variations in properties of these alloys are discussed.     

Vortex structure in superconducting iron pnictide single crystals

The vortex structure in the iron pnictide single crystals Ba_1?x K _x Fe₂As₂ and Sr_1?x K _x Fe₂As₂ of the 122 type and SmFeAsO_1?x F _x of the 1111 type has been investigated using the decoration method. In all of the crystals under investigation, no regular vortex lattice has been revealed in the magnetic field range up to 200 Oe. The disordered vortex structure is discussed in view of the vortex pinning in single crystals.     

Evidence of bcc Mn epitaxial growth in Mn/M<Subscript>x</Subscript>V<Subscript>1–x</Subscript>(001) (M = Fe,Nb) superlattices

This study is dedicated to the growth of bcc Mn by molecular beam epitaxy, in order to look at the magnetic properties of bcc Mn near room temperature. For this purpose, Mn is deposited on bcc M_xV_1-x(001) alloy lattices (M = Fe or Nb) for which the lattice spacing is tunable by varying the concentration x. We first show that the parameter of the M_xV_1-x alloy's buffer layers can be adjusted from 2.95 ? to 3.3 ? depending on x and M. Three different structures in Mn films grown on these buffer layers are observed depending on the in-plane spacing of the initial M_xV_1-x lattice. Thick Mn films are always found to grow epitaxially in the Mnstructure. For moderate thicknesses larger than 4 atomic planes, Mn grows in an unidentified structure. Finally, up to four deposited atomic planes, Mn is found to grow in a tetragonal structure close to a bcc one on Fe(001), Fe_xV_1-x(001) and Nb_xV_1-x(001) for . This tetragonal structure is shown to be a distorsion of a Mn bcc structure with . Except for ultra-thin Mn films deposited on Fe(001), no macroscopic magnetization is detected in our strained bcc Mn samples. These results are compared to theoretical predictions. Received 21 June 1999     

In situ neutron diffraction study (300-1273 K) of non-stoichiometric strontium ferrite SrFeOx

The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeO_x (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeO_x changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeO_x is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeO_x to be described in terms of a solid solution of the composition end members. Cubic SrFeO_x at high temperature is found to closely obey Vegard's law. The density of cubic SrFeO_x is also found to exhibit a linear relationship with composition.     

Structural phase transition in substituted La2CuO4 and Pr2CuO4−y

The structural phase transition from orthorhombic (T) phase to tetragonal (T′) phase in substituted La_2−x R _x CuO₄ (R = Pr, Nd, Sm, Eu and Gd) and T′ to T-phase in Pr_2−x M _x CuO_4−y (M = Sr, Ca) has been studied by X-ray diffraction technique. The T-phase of La₂CuO₄ is transferred to T′ phase abruptly atx=0.8, 0.4, 0.4, 0.3 and 0.4 respectively for substitution of Pr, Nd, Sm, Eu and Gd for La in La₂CuO₄ without evidence of the T* phase. The T′ structure of Pr₂CuO₄ (x = 0.0) gets transformed to the T* structure at 30% Ca doping (x=0.6) and then to the T structure at 50% Ca doping (x=1.0), while for Sr-contentx=0.0, 0.4 and 1.0 it shows T′, T* and T structure respectively.     

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     

Antiferromagnet-ferromagnet transition in α-MnxS manganese sulfides

Off-stoichiometric manganese monosulfides α-Mn_xS (1≤x≤1.25) are synthesized, and their crystal structure and magnetic properties are studied in the 4.2-to 300-K range. The compounds have a NaCl fcc lattice. Increasing the manganese ion concentration x in the antiferromagnetic semiconductors α-Mn_xS is found to result in concentration-(x _c ～ 1.05) and temperature-driven (T _c ～ 50 K) magnetic transitions from the antiferromagnetic to ferromagnetic state, with the cubic structure remaining unchanged.     

The discovery of a 2H–6H solid state transformation in ZnxCd1−xS single crystals

Single crystals of Zn_xCd_1?xS have been grown from the vapour phase at 1100°C in the presence of H₂S gas. X-ray diffraction studies of the as-grown crystals show that polytypism and stscking faults occur in Zn_xCd_1?xS crystals for x ? 0.94. It is observed that for 0.92 < x < 0.98 the 2H structure of Zn_xCd_1?xS crystals transforms to a disordered 6H structure on annealing in vacuum around 600°C. For 0.95 < x < 0.98 this 6H structure finally transforms to a disordered 3C structure on annealing further at higher temperatures around 800°C. The structural transformations occur through a non-random insertion of stacking faults, as revealed by the diffuse streak joining the X-ray diffraction maxima along the 10.L reciprocal lattice row. Experimental investigation of the diffuse intensity distribution, as recorded on a single crystal diffractometer from partially transformed single crystals, reveals that the mechanism of the transformation is very different from that reported for the same transformation in silicon carbide and cannot be described in terms of a single-parameter model of non-random deformation faulting.     

金属有机物化学气相沉积法生长Ga2（1-x）In2xO3薄膜的结构及光电性能研究

采用金属有机物化学气相沉积（MOCVD）法在蓝宝石（0001）衬底上制备出了Ga_2（1-x）In_2xO₃（x=01—09）薄膜,研究了薄膜的结构、电学和光学特性以及退火处理对薄膜性质的影响.测量结果表明：当In组分x=02时,样品为单斜β-Ga₂O₃结构;x=05的样品,薄膜呈现非晶结构,退火处理后薄膜结构得到明显的改善 关键词： 金属有机物化学气相沉积 2（1-x）In_2xO₃薄膜')" href="#">Ga_2（1-x）In_2xO₃薄膜 蓝宝石衬底 退火     

Magnetotransport and magnetic properties of sulfospinels Zn x Fe1−x Cr2S4

Cr-based chalcogenide spinels, which do not have heterovalency and distortion-induced ions such as manganese oxides with perovskite structure, have demonstrated the existence of colossal magnetoresistance. In order to investigate the magnetotransport phenomena and magnetic properties of sulfospinels Zn _x Fe_1?x Cr₂S₄, polycrystalline Zn _x Fe_1?x Cr₂S₄ samples were synthesized in the 0?≤?x?≤?0.2 range by a solid reaction method. The crystal structure for x?=?0.05, 0.1, and 0.2 turned out to be cubic at room temperature by X-ray diffraction measurement. In magnetoresistance measurement, Zn _x Fe_1?x Cr₂S₄ samples indicate that this system is semiconducting below about 150 K. The temperature of maximum magnetoresistance is almost consistent with Curie temperature. The isomer shift and the electric quadrupole shift of Zn _x Fe_1?x Cr₂S₄ samples by Mössbauer experiment show that Fe²⁺ ions occupy the tetrahedral site in the spinel structure. As the Zn ions are substituted for Fe ions, the Jahn–Teller relaxation slows down and the electric quadrupole shift increases. The magnetotransport phenomena of Zn _x Fe_1?x Cr₂S₄ is related to Jahn–Teller effect and half-metallic electronic structure, which are different from the double exchange interactions of the manganite La–Ca–Mn–O system or the triple exchange interactions of sulfospinel Cu _x Fe_1?x Cr₂S₄.