Ca掺杂Nd1.85Ce0.15CuO4-δ体系的输运性质研究

为了研究Nd_1.85Ce_0.15CuO_4-δ体系中载流子的电荷性质，分别在Nd_1.85Ce_0.15CuO_4-δ中用Ca^2＋取代Nd^3＋制备了Nd_1.85-xCe_0.15Ca_xCuO_4-δ样品，在Nd₂CuO_{4-δ< 关键词：}     

Nd1.85Ce0.15CuO4－δ单晶c-轴方向电阻的低场行为

采用自助熔剂缓冷法成功地生长出了Nd_1.85Ce_{0. 15}CuO_4-δ单晶，其零场下零电阻温度约为21K. 在0—0.5T范围内分别测量了磁场平行和垂直样品表面的电阻转变曲线以及0.5T不同角度下的电阻转变曲线. 结果显示磁场平行和垂直样品表面时的转变温度T_p随磁场的变化均服从H=H₀(1-T_p(h)/T_p(0))²关系. 0.5T 关键词： 1.85Ce_0.15CuO_4-δ单晶')" href="#">Nd_1.85Ce_0.15CuO_4-δ单晶 输运性质     

原子簇La8-xBaxCuO6的原子磁矩和自旋极化的电子结构研究

利用MS-Xα方法研究了化合物La_2-yBa_yCuO₄的原子磁矩和自旋极化的电子结构.理论计算得到母相氧化物La₂CuO₄的Cu原子磁矩为0.37μ_B，与实验值0.48±0.15μ_B基本一致. 研究结果显示, 由于Ba原子对部分La的替代，使构成化合物的基本原子簇La_8-xBa_xCuO₆的 关键词： 电子结构 自旋极化 磁矩 态密度 超导电性     

薄膜厚度对La1.85Sr0.15CuO4薄膜结构和超导电性的影响

使用直流同轴磁控溅射法,在SrTiO₃(STO)衬底上成功制备出c取向的La_1.85Sr_0.15CuO₄(LSCO)超导薄膜.通过电输运测量系统和X射线衍射仪研究了薄膜厚度对LSCO(x＝0.15)薄膜电学性质和晶体结构的影响.实验证明随着膜厚增加,(006)衍射峰的半高宽(Full Width at Half Maximum,FWHM)逐渐减小,薄膜的取向性增强,与此同时,薄膜的超导转变温 关键词： 1.85Sr_0.15CuO₄薄膜')" href="#">La_1.85Sr_0.15CuO₄薄膜 超导电性 晶体结构     

Nd-Ni二元系合金相图

本文用X射线衍射和差热分析方法测定了Nd-Ni二元系合金相图。在此二元系中观察到如下八个金属间化合物:Nd₃Ni(熔点为590℃),Nd₇Ni₃(熔点为616℃),NdNi(熔点为780℃),NdNi₂(940℃分解),NdNi₃(1030℃分解),Nd₂Ni,(1234℃分解),NdNi₅(熔点为1420℃)和Nd₂Ni _关键词：     

Nd2(Fe1-xMnx)14B的低温内禀矫顽力

当x<0.5时,Nd₂(Fe_1-xMn_x)₁₄B可形成四方晶体结构,空间群为P4₂/mnm。在低温下,该赝三元化合物的大块铸态样品具有高矫顽力。此矫顽力不依赖于热处理等工艺过程,因此具有内禀性质。内禀矫顽力 _iH_c与样品的成分有关。Nd₂(Fe_1-xMn_x)₁₄B的起始磁化曲线具有传播场H_p,并且H_p的数值与 _iH_c接近。这表明内禀矫顽力是由畴壁钉扎造成的。研究了 _iH_c与温度的变化关系,并估算了钉扎位垒的强度。测量了Nd₂(Fe_1-xMn_x)₁₄B的居里温度和饱和磁化强度。在此赝三元化合物中,交换作用随Mn对Fe的替换而急剧降低。这使得畴壁厚度变窄。Nd₂(Fe_1-xMn_x)₁₄B的磁化和反磁化行为可用窄畴壁的特征来解释。 关键词：     

基于二缺位钨多酸化合物的二维相关红外光谱研究

通过水热法合成了一例新颖的稀土钨多酸化合物H₂₆(C₂H₈N₂H₂)K(H₂O)[K(H₂O)Nd₈(H₂O)₂(W₃O₁₂)(SiW₁₀O₃₈)₄]·18H₂O 1。该化合物的不对称单元由两个[SiW₁₀O₃₈]^12-通过一个{Nd₄(H₂O)¹²⁺}结构单元和W₃O₁₂连接而成。化合物1簇阴离子通过K离子连接成一维无限链,再通过氢键连接成二维平面结构。针对该化合物,做了一系列表征,测试了其二维相关红外光谱,并对其作了详细分析,结果说明化合物1簇阴离子振动偶极矩对磁...     

Nd2(Fe,Si)17合金的结构与磁性

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：     

热处理对非晶态合金Nd4Fe96-xBx磁性的影响

本文研究了用单辊急冷方法制备的非晶态合金Nd₄Fe_96-xB_x的晶化,以及热处理对其硬磁性和相组成的影响,发现非晶态合金Nd₄Fe_96-xB_x的晶化温度比相同B含量的非晶态合金Fe_100-xB_x高120—190K,X射线衍射和热磁测量表明,15≤x≤25的样品晶化相是由Nd₂Fe₁₄B(T 关键词：     

Zn,Ni,Mg高掺杂La1.85Sr0.15CuO4的晶体结构比较

对Zn,Ni,Mg高掺杂的La_1.85Sr_0.15CuO₄(LSCO)超导体的X射线衍射谱进行了仔细的分析,从而获得了各掺杂样品的晶格常量、原子结构参量及衍射的峰形参量,比较了不同掺杂所引起的晶体结构的差异,计算了由于掺杂所产生的晶格内部的微应变,结果表明非磁性金属Zn,Mg掺杂比磁性金属Ni掺杂更强烈地抑制了LSCO的超导电性可能与材料中晶格的微应变有关. 关键词： 1.85Sr_0.15CuO₄')" href="#">La_1.85Sr_0.15CuO₄ 磁、非磁掺杂 原子结构参量 晶格微应变     

On the interpretation of the phase diagram of La<Subscript>2−x</Subscript>M<Subscript>x</Subscript>CuO<Subscript>4</Subscript>

The difference between the phase diagrams of La_2?x(Ba,Sr)_xCuO₄ and Nd_2?xCe_xCuO₄ is discussed. It is proposed that the discrepancy of x-values corresponding to the transition from antiferromagnetic dielectric state to conducting one (respectively, x≈0.06 in La_2?x(Ba,Sr)_xCuO₄ and x≈0.125 in Nd_2?xCe_xCuO₄) results from non-homogeneous doping of La_2?x(Ba,Sr)_xCuO₄ over the range 0.06<x<0.125, when localized holes are added to each second CuO₂ layer. Therefore the actual phase diagram of the “holedoped” superconductor La_2?x(Ba,Sr)_xCuO₄ coincides with one for the “electron-doped” superconductor Nd_2?xCe_xCuO₄. It is shown that all features observed in La_2?x(Ba,Sr)_xCuO₄ around x=0.125 are clarified on this basis.     

Comparison of the single-electron and many-electron mechanisms of the concentration dependence of the HTSC cuprate band structure

The band structure of the Nd_{2 ? x} Ce _x CuO₄HTSC is calculated using the LDA+GTB method, which combines the local density approximation (LDA) and the generalized tight-binding (GTB) method. Two mechanisms of the concentration dependence of the band structure (single-electron and many-electron mechanisms) are taken into account. It is demonstrated that the main contribution to the evolution of the band structure with doping comes from the many-electron mechanism.     

Intermediate dimensional character of charge transfer excitation modes in a two-leg cuprate ladder

Collective charge modes in the cuprate ladder compound Sr₁₄Cu₂₄O₄₁ are studied over the one-dimensional Brillouin zone using resonant inelastic X-ray scattering. Low energy (2-4 eV) spectral weight across the Mott gap is dominated by a broad, dispersive feature containing two distinct peaks that may be interpreted as independent modes. Details of low energy dispersion, intensity distribution across the Brillouin zone and peak composition fall between the characteristic spectra of quasi-1D (e.g. SrCuO₂) and -2D cuprates (e.g. Nd₂CuO₄). We demonstrate that dispersion and splitting between the two observed modes can be understood in a variant of the strong coupling limit (Hubbard-U?t) with a single band Hubbard model.     

Valence states of copper atoms in cuprates determined from the change in the electron-capture constant of 64Cu

The change in the ⁶⁴Cu electron-capture constant for the compounds Cu₂O, YBa₂Cu₃O₇, YBa₂Cu₃O₆, Nd₂CuO₄, Nd_1.8Ce_0.2CuO₄, La₂CuO₄, La_1.7Sr_0.3CuO₄, Tl₂Ba₂CaCu₂O₈, and Bi₂Sr₂CaCu₂O₈ has been measured. It is concluded that the copper in YBa₂Cu₃O₇, Nd₂CuO₄, La₂CuO₄, La_1.7Sr_0.3CuO₄, Tl₂Ba₂CaCu₂O₈, and Bi₂Sr₂CaCu₂O₈ is exclusively divalent, whereas in Cu₂O, YBa₂Cu₃O₆, and Nd_1.8Ce_0.2CuO₄ univalent copper is present. Fiz. Tverd. Tela (St. Petersburg) 39, 1793–1794 (October 1998)     

μSR on the novel heavy‐fermion system Nd2-yCeyCuO4

The magnetic correlations in Nd_2-yCe_yCuO₄ have been studied by zero and longitudinal field μSR. Nd_1.8Ce_0.2CuO₄ reveals a saturation of the muon relaxation rate below 0.5 K. Even down to 70 mK LF spectra evidence spin fluctuations in the dynamic regime with a rate of \sim 10⁹ s^-1 excluding long range magnetic order or spin glass freezing. The average Nd moment is estimated to be \approx 0.2\mu_B, i.e., strongly reduced from the value determined for the ground state Kramers doublet of Nd₂CuO₄. Extending former μSR measurements on Nd₂CuO₄, a gradual enhancement of the internal field has been detected below 10 K which is accompanied by an increase of the relaxation rate. These results are attributed to the development of ordered Nd moments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Material characterization of superconducting T′-Nd2CuO4 films synthesized by metal organic decomposition

Recently we have achieved superconductivity in T′-RE₂CuO₄ (RE = Pr, Nd, Sm, Eu, and Gd), films by metal organic decomposition (MOD). In this article, we first report the cation off-stoichiometry effect, which aims at screening out the possibility of hole doping by cation deficiencies. We also investigated the structure and microstructure of superconducting T′-Nd₂CuO₄ films synthesized by MOD. This investigation aims at elucidating why MOD-grown Nd₂CuO₄ films become superconducting whereas our previous Nd₂CuO₄ films grown by molecular beam epitaxy were not superconducting.     

Magnetic order in La2-x Bax CuO4 and La1.6-x Nd0.4 Srx CuO4 for x=0.125

We present μSR experiments on La_2-x Ba_x CuO₄ and La_1.6-x Nd_0.4 Sr_x CuO₄ for x=0.125. Both of these materials order magnetically with T_N\approx30\ K, while a superconducting sample of La_1.4 Nd_0.4 Sr_0.2 CuO₄ showed no evidence for static copper moments. Our results support the conclusion that the so‐called “1/8” anomaly in La_2-x Ba_x CuO₄ is a result of static (pinned) charge segregation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photopyroelectric (PPE) Spectroscopy of Surface Reflectance for Nd2−xCexCuo4 Single Crystals

The relevance of the sample surface reflectance Rs when applying the photopyroelectric technique is demonstrated and, based on this, a method for determining Rs spectra of opaque samples, is presented. Measurements were done on single crystals of Nd₂CuO₄ and Nd_1.97Ce_0.03CuO₄ and the results were found in good agreement with the data obtained by optical methods.