钙钛矿锰氧化物La0.7Sr0.3MxMn1-xO3(M=Cr,Fe)的巨磁电阻效应与磁性

研究了溶胶-凝胶法制备氧化物巨磁电阻材料的工艺,制备了La_0.7Sr_{0.3< /sub>CrxMn1-xO3(x=0,0.10,0.15)和La0.7Sr0.3FexMn1-xO3(x=0.05,0.10,0.16)两 系列的单相钙钛矿锰氧化物多晶样品,并研究了Cr,Fe替代La0.7Sr0.3MnO3中部分Mn后对其结构、磁性和巨磁电阻性质的影响.观察到La0.7 Sr0.3Cr0.15Mn0.85O3和La0. 7Sr0.3Fe0.05Mn0.95O3两个样品的 电阻-温度曲线都出现了双峰.定性讨论了可能产生双峰的机制.随Cr(或Fe)替代量的增加, 材料的居里温度很快下降,铁磁性减弱,导电性降低,巨磁电阻效应增强.但与Fe掺杂相比 ,相同数量的Cr掺杂对材料的影响要小. 关键词： 巨磁电阻效应 溶胶-凝胶工艺 电阻-温度曲线 金属绝缘体转变}     

Y1-xCaxBa2Cu3-xMxO7-δ (M=Fe,Ni)体系的超导电性

本文报道,通过对Y_1-xCa_xBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系样品的晶体结构、氧含量、正常态电阻率与温度的关系,以及超导转变温度等测量,并与YBa₂Cu_3-xMxO_7-δ(M=Fe,Ni)体系进行比较,发现Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系的T_c显著地高于相应x值的YBa₂Cu_3-xFe_xO_7-δ体系,而Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系则相反,T_c低于仅Ni替代的体系,表明Ca和Fe同时替代时两者引起的载流子浓度(n_H)变化相互补偿,抑制了仅Fe替代时引起的n_H和T_c急剧下降;而作Ca和Ni同时替代时主要的不是两者引起载流子浓度变化的相互补偿,Ca和Ni替代效应之间的关联较弱。作者认为,对Y_1-xCa_xBa₂Cu_3-xFe_xO_7-δ体系属于CuO₂平面外的元素替代,这时载流子浓度是决定Tc的主要因素;而对Y_1-xCa_xBa₂Cu_3-xNi_xO_7-δ体系,由于Ni²⁺离子主要占据Cu(Ⅱ)位,它导致磁拆对效应,Ni²⁺离子的拆对效应是引起T_c下降的直接原因。 关键词：     

Sm2(Fe,M)17C1.5(M=Ga,Si)化合物的形成和磁性

用电弧炉熔炼方法制备了Ｓｍ₂Ｆｅ_17-xＭ_xＣ_1.5（Ｍ＝Ｇａ，Ｓｉ）化合物，研究了它们的形成、结构与磁性。实验结果表明，用Ｇａ替代Ｆｅ，当２≤ｘ≤６时，可形成Ｔｈ₂Ｚｎ₁₇型单相化合物，而Ｓｉ的替代仅在ｘ＝２时为单相结构。居里温度随Ｇａ含量的增加从ｘ＝２时的６３３Ｋ下降到ｘ＝６时的３５１Ｋ，Ｓｍ₂Ｆｅ₁₅Ｓｉ₂关键词：     

Low-temperature specific heat and resistance for the heavy-electron metals CeCu6-xMx （M=Ni,Zn）

The specific heat and resistance of CeCu_{6-x}M_x (M=Ni,Zn) have been studied in the concentration range where they still retain the orthorhombic structure. The coefficient c of -ln T term in resistance R=R_0+bT-cln T, as well as the γ, have been found to vary in opposite directions with increasing x for Ni and Zn substitutions. The physical mechanism is discussed.     

热压制备(AgSbTe2)100-x-(GeTe)x合金的热电性能

以Pb粉、Te粉、Ag粉、Ge粉为原材料,在真空气氛下合成(AgSbTe₂)_100-x-(GeTe)_x (x=80---90) (TAGS)合金热电材料, X射线衍射(XRD)分析表明,热压烧结后合金具有低温菱形结构. 通过热压烧结法将TAGS粉末制备成块体材料,运用XRD和扫描电子显微镜对材料的物相成分、 晶体结构和形貌进行了表征.采用直流四探针法测定样品的电导率,当样品两端的温差为1---4℃ 的情况下测量Seebeck系数.通过材料热电性能测试,研究了30---500℃温度范围内不同组分 样品性能参数的变化.结果表明,所制备的TAGS热电材料具有纳米结构, 其性能随着组分的变化而变化, TAGS-80具有较好的热电性能,在530℃时具有最高热电优值(ZT=1.80).     

Electrical conductivity of (Bi,Pb)2MO4 (M = Pd,Pt) linear chain compounds

Partial oxidation of Pd in Bi₂PdO₄ is achieved by substitution of Pb²⁺ for Bi³⁺ up to Bi₁₉₁Pb₀₀₉PdO₄, partial oxidation is necessary to stabilize the isostructural Pt compound, Bi_1?xPb_xPtO₄ within the range 0.33 ? x ? 0.52. In both cases, the tetragonal cell c parameter, therefore metal-metal distance $\text{(d}{}_{\mathrm{<mtext>M?M</mtext>}}\text{=}\text{c}\text{2}\text{)}$, decreases linearly with increasing mean oxidation degree (MOD) of transition metal atom For the insulator B1₂CuO₄, no substitution occurs Powder electrical conductivity measurements of the partially oxidized compounds show that these materials are semiconductors Platinum compounds exhibit relatively high conductivities $\text{(σ?10 (Ω}\text{cm}\text{)}{}^{\mathrm{?1}}\text{)}$ and low activation energies (?0 02 eV) with small variations with x Palladium compounds exhibit lower conductivities which linearly increases with MOD These electronic properties are comparable with those of the most one-dimensional Pt or Pd chain conductors.     

Magnetic susceptibility and magnetic resonance study of acceptor doped fullerenes C60(MF6)2 (M=As, Sb, P)

In order to check whether superconductivity occurs in the acceptor doped fullerenes C₆₀(MF₆)₂ (M=As, P, Sb) and to study their magnetic and structural properties, we have carried out magnetic, EPR and NMR measurements of these compounds. Temperature dependences of magnetic susceptibility down to 5 K and field dependences of magnetic moment at 5 K show no ‘bulk’ transition in superconducting state. Some reasons of the absence of superconductivity, such as insufficient charge transfer between C₆₀ and intercalated species and inhomogeneity of the compounds under study, are discussed.     

磁共振法研究(Fe1-xCox)84Zr3.5Nb 3.5B8Cu1纳米晶薄带的磁各向异性

铁磁共振（FMR）实验研究(Fe_1-xCo_x)₈₄Zr_{3.5 Nb3.5B8Cu1（x=0.0,0.2,0.4,0.6, 0.8）合金薄 带的各向异性，易轴在薄带的横向方向,同等宽度样品 的各向异性常数K′随Co掺杂量的增加而减小, K′值在4.67×10^-5　J/m（x=0. 0）到 2.54×10^-5　J 关键词： 铁磁共振 各向异性常数 低场非共振信号 磁化过程}     

Synthesis and magnetic properties of Pr(Fe 1-xCo x) 2 and Pr 1-yTb y(Fe 0.4Co 0.6) 2 alloys

Measurement of X-ray diffraction, magnetization and magnetostriction was made on the Pr(Fe_1-xCo_x)₂ (x=0.4, 0.5 and 0.6) and Pr_1-yTb_y(Fe_0.4Co_0.6)₂ (y=0, 0.1, 0.2 and 0.3) alloy series. It was found that a cubic phase with the MgCu₂ structure can be obtained in the Pr(Fe_1-xCo_x)₂ series only at x=0.6. The Pr_1-yTb_y(Fe_0.4Co_0.6)₂ system has the cubic MgCu₂ structure over the studied range for y. The lattice constant and magnetization decrease and the Curie temperature increases with increasing y. At 7 K, Pr_1-yTb_y(Fe_0.4Co_0.6)₂ samples are found to have huge intrinsic coercivities, which are associated with narrow domain walls. It is also found from X-ray measurement that in Pr_1-yTb_y(Fe_0.4Co_0.6)₂ the spontaneous magnetostriction ₁₁₁ increases due to Tb substitution, while the saturation magnetostriction _s is much lower than ₁₁₁. This can be attributed to the large value of ₁₀₀ with an opposite sign to ₁₁₁, which may be caused by the filling of the d band due to Co substitution. PACS 75.80.-g; 61.10.-i; 75.60.-d     

Transport properties of magnetically ordered amorphous (Fe100-xMnx)75P15C10 alloys

The resistivity , the magnetoresistance Δ and the Hall resistivity _H of alloys up to 30% Mn have been measured using amorphous ribbons of these materials. The temperature and field dependences of and _H suggest a variety of structural and spin scattering centers; in particular, (T) appears to be governed by structural (isotropic) scattering centers while _H(T) is dominated by topological (anisotropic) spin scattering centers, one of which probably is a “spin-hole”.     

远红外光纤材料(MnF2)x(BaCl2)100-x玻璃结构的EXAFS和WAXS研究

本文用扩展X射线吸收谱(EXAFS)和X射线大角散射谱(WAXS)对远红外光纤材料复合卤化物玻璃(MnF₂)_x(BaCl₂)_166-x(x=65,60,55)的短程结构进行了研究。从MnK吸收限的EXAFS和样品的非晶衍射图,得到了Mn原子的近邻原子配位信息。结果表明F,Cl原子在Mn原子周围形成了混合配位的八面体(MnCl₂F₄),这些八面体以Mn—F键为桥键连成“之”字型 关键词：     

YTi(Fe1-xCox)11的磁性和穆斯堡尔谱的研究

YTi(Fe_1-xCo_x)₁₁在012型四方结构,居里温度随Co含量的增加而提高,本文为了揭示YTi(Fe_1-xCo_x)₁₁磁性与微观结构的联系,对这一系列化合物进行穆斯堡尔谱研究,在室温下,测量YTi(Fe_1-xCo_x)₁₁(其中x=0.0,0.2,0.4)的穆斯堡尔谱,最佳拟合结果证实在这种化合物中,Co原子优先占据j和f晶位,在所测样品中,超精细场在x=0.2处出现极值,这与YTi(Fe_1-xCo_x)₁₁饱和磁化强度测量结果相符合。并对YTi(Fe_1-xCo_x)₁₁,Y₂(Fe_1-xCo_x)₁₄和YTi(Fe_1-xCo_x)₁₁的穆斯堡尔谱的实验结果进行比较,分析在YTiFe₁₁中与Y₂Fe₁₄B中的3d电子能带结构的差异。 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.     

Thermoelectric power of the vitreous electrolyte (AgI)0.79(Ag2O.B2O3)0.21

We have determined the thermoelectric power ? of the high ionic conductivity glass (AgI)_0.79(Ag₂O.B₂O₃)_0.21; ? is negative throughout the investigated T range, 320–500 K. The heat of transport of the mobile Ag⁺, Q_Ag, taken as the slope of the straight line fitting ? versus 1/T, is quite lower than the activation energy obtained from conductivity data, viz. Q_Ag = 2.81 kcal/mole^-1 < E_act = 4.34 kcalmole^-1. To circumvent this discrepancy, the analysis of the experimental data is carried out as follows: (i) it is supposed that Q_Ag = E_act in agreement with the free ion theory for solid electrolytes; (ii) the vibrational part of the silver ion entropy, S(Ag⁺, vib), is assumed to be equal to the entropy of silver, S(Ag); (iii) on the ground of a structural model for this kind of glasses, the ideal configurational entropy of the mobile Ag⁺, S(Ag⁺, conf)_id, is evaluated through a statistical approach. The ideal ionic entropy is defined as S(Ag⁺)_id = {S(Ag⁺, vib) + S(Ag⁺, conf)_id}; (iv) the difference {S(Ag⁺)_exp - S(Ag⁺)_id} is viewed as an excess entropy and is described according to the classical model of the regular solutions.     

Rapid preparation of Mg（B1-xCx）2 superconductor using hybrid microwave method

The crystal structure and the superconductivity for samples Mg（B1-xCx）2 （0〈 x 〈0.09） prepared by a hybrid microwave synthesis have been investigated. The starting material B10C is also obtained by using the microwave method. The carbon can distribute uniformly in the Mg（B1-xCx）2 samples because boron and carbon are mixed on an atomic scale in the staring material B10C. The dependences of both lattice parameters and superconducting transition temperature Tc on carbon content accord with those reported in the literature. The upper critical field He2 at 20 K can be enhanced from about 4.3 T for x = 0 to 10 T for x = 0.05. The critical current density Jc of Mg（B0.95 C0.05）2 is 1.05×10^4 A/cm^2 at 20 K and 1 T.     

THE INFLUENCE OF Co SUBSTITUTION ON THE MAGNETIC PROPERTIES AND THE GIANT MAGNETO-IMPEDANCE EFFECT OF (Fe1-xCox)84Zr3.5Nb3.5B8Cu1

The microstructure, magnetic properties and the giant magneto-impedance (GMI) effect of the nanocrystalline (Fe_1-xCo_x)₈₄Zr_3.5Nb_3.5B₈Cu₁ ribbons have been studied. With increasing Co concentration, the nanocrystallized grain size and volume fraction of the α-Fe(Co) phase decrease under the same annealing condition, while the coercivity H_c increases from 1.92 A/m at x=0.0 to 30.38 A/m at x=0.8. The effective permeability drops sharply with increasing Co concentration so that the GMI effect goes down. A value of more than 380% for the magneto-impedance(MI) ratio was measured at frequency f=2.5 MHz and the sensitivity can reach 0.9% (A/m)^-1 for Fe₈₄Zr_3.5Nb_3.5B₈Cu₁ ribbon. When x is equal to 0.8, the MI ratio drops to about 30% and the sensitivity only reaches a value of lower than 0.025% (A/m)^-1. The concise analysis in theory is also expounded.     

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：     

R2(Fe1-xAlx)14B的内禀磁性和永磁性能(R=Nd和Y)

本文研究了Al在R₂(Fe_1-xAl_x)₁₄B多元合金中的固溶度(R=Nd和Y),当x<0.1时,可形成四方结构。研究了在此类合金中,饱和磁化强度、居里温度、磁晶各向异性等内禀磁性,以及矫顽力和磁能积等永磁性能随Al含量的变化。发现以Al代换Fe时,使铁次点阵的磁晶各向异性出现极值;同时以Al代换Fe时,可使磁体的矫顽力显著提高。以Co和Al同时对Fe进行代换,制造成分约为Nd_16.5B _关键词：     

Magnetic susceptibility of (IPA)2FeCl4, (IBuA)2FeCl4 and (IPA)2CuCi4 (IPA = isopropylammonium ion and IBuA = isobutylammonium ion)

The magnetic susceptibility of (IPA)₂FeCl₄, (IBuA)₂FeCl₄ and (IPA)₂CuCl₄, where IPA = (CH₃)₂CHNH⁺₃ and IBuA = (CH₃)₂CHCH₂NH⁺₃, were measured in the temperature range form 80 K up to a temperature near the melting points of the samples. The results obtained were interpreted in termw of a canted two-dimensional antiferromagnet. The variation of the magnetic susceptibility with the change in the composition was also discussed.     

Anomalous magnetostrictive effects in （La1—xTbx）2／3Sr1／3 MnO3

A series of (La_{1-x}Tb_x)_{2/3}Sr_{1/3}MnO_3 polycrystalline samples has been studied by means of x-ray diffraction, magnetostriction, and thermal expansion measurements. It has been found that this series undergoes a phase transition from a rhombohedral to an orthorhombic form at the doping level x≈0.20 at room temperature accompanied by an anisotropic magnetostriction up to －50×10^{-6} under a magnetic field of 1T. The linear and volume magnetostrictions vary with chemical composition, even change sign. At T=80K, the magnetostrictions for the samples of x=0.20 and 0.40 exhibit different behaviours. The sample of x=0.20 has positive volume and linear magnetostrictions and a negative anisotropic magnetostriction, while the sample of x=0.40 has an opposite behaviour. The magnitude of volume magnetostriction for both the samples is essential (～10^{-4}) at T=80K under a magnetic field of 4T. We conclude that these anomalous effects are due to the charge delocalization and the structural phase transition between orthorhombic and rhombohedral forms induced by the applied magnetic field.