Fex（In2O3）1—x颗粒膜磁性的研究

报道了“铁磁金属－半导体基体”Ｆｅｘ（Ｉｎ２Ｏ３）１－Ｘ颗粒膜的磁性研究。根据低场磁化率Ｘ（Ｔ）温度关系和不同温度下的磁滞回线研究表明：膜中的Ｆｅ颗粒有大小不同的两种尺度,随温度降低,颗粒膜的磁特性由超顺磁态转变为超顺磁和铁磁的混磁态,最后在１０Ｋ变为类反铁磁态;在截止温度以上,其ＭＳ（Ｔ）关系符合Ｂｌｏｃｈ的Ｔ＾３／２定律。     

La2／3Ca1／3MnO3掺Bi的磁电阻行为

研究了Ｌａ（２－ｘ）Ｂｉｘ／３Ｃａ１／３ＭｎＯ３体系的电阻行为和磁性转变，当ｘ＝０．０，０．２时，样品表现为铁磁转变，居里温度Ｔｃ分别为２６５Ｋ和２４５Ｋ，铁磁转变伴随着半导体－金属转变，对应于磁电阻效应的极大值；当ｘ＝０．４时，样品表现为复杂的磁性转变，样品的电阻率为半导体特性，对应的磁性转变没有半导体，金属转变发生，在ｘ＝０．４和０．６两个样品中，１Ｔ外场下８５Ｋ时获得大于８６％的巨磁电阻效应     

氰基桥联铬(Ⅲ)-镍(Ⅱ)和铬(Ⅲ)-铜(Ⅱ)多核配合物的合成、表征和磁性质研究(英文)

合成了配合物［ＭＬ］３［Ｃｒ（ＣＮ）６］２·ｘＨ２Ｏ（Ｍ二Ｎｉ,Ｌ＝三（２－胺基乙基）胺（ｔｒｅｎ）,ｘ＝ Ｏ; Ｍ＝ Ｃｕ, Ｌ＝二丙烯三胺（ ｄｐｔ）, ｘ＝ ８）和［ Ｍ（ ｔｎ）２］２［Ｃｒ（ ＣＮ）６ ］ＣＩＯ４· ＸＨ２ Ｏ（ ｔｎ＝ １, ３－丙二胺,Ｍ＝ Ｎｉ,ｘ＝ Ｏ;Ｍ＝ Ｃｕ,ｘ＝ ２）．用元素分析、ＩＣＰ分析、ＩＲ光谱等对配合物进行了表征,测定了它们的磁性质．变温磁化率研究表明：［Ｃｕ（ｄｐｔ）］３［Ｃｒ（ＣＮ）６］２·８Ｈ２Ｏ中存在弱的铁磁（Ｔ＞ １６．６３Ｋ）和反铁磁（Ｔ＜ １６．６３Ｋ）相互作用;［Ｃｕ（ｔｎ）２］２［Ｃｒ（ＣＮ）６］ＣＩＯ４·２Ｈ２Ｏ中存在反铁磁相互作用（Ｔ＜５．８６Ｋ）．研究发现,这些配合物有两种结构类型：氰基桥联结构和双配合盐结构．     

Nd_(0.5)Sr_(0.5-x)Ca_xMnO_3(x=0.1,0.2)多晶的电子自旋共振研究

研究了多晶样品Nd_(0.5)Sr_(0.5-x)Ca_xMnO_3(x=0.1,0.2)的磁性.实验结果表明,样品的单相性好,无杂相,空间群为Pbnm.随着温度的降低,样品先后经历了3次磁性转变,分别为顺磁-铁磁转变TC、电荷有序转变TCO和奈尔温度转变TN;在TC以上,系统处于顺磁态,在TC-TCO范围内,系统处于铁磁-顺磁共存态,在TCO-TN范围内,系统处于反铁磁-铁磁-顺磁共存态,在TN以下,系统主要处于反铁磁态.     

类钙钛矿化合物Ca(Mn3-xCux)Mn4O12的磁电阻效应

在常压和较低温度(1073K)下利用溶胶-凝胶法制备了成分为Ca(Mn3-xCux)Mn4O12的化合物,X射线衍射图表明当x≤1.5时化合物呈单一钙钛矿相.所有样品均未观测到金属-绝缘体转变,但随成份的改变有反铁磁-铁磁转变发生.它们的磁电阻随温度呈线性变化系.对x＝1.5的样品,在77K和3T磁场下的磁电阻可达37%.     

Fe_（1－x）Ni_x合金超细微粒的磁性及穆斯堡尔谱研究

气相蒸发法制备的Ｆｅ１－ｘＮｉｘ合金超细微粒，平均粒径约为２０ｎｍ。利用振动样品磁强计、ｘ射线衍射分析仪以及穆斯堡尔谱仪分析了样品的磁性、相组成随ｘ的变化关系。结果表明：８０Ｋ和２９５Ｋ温度下，ｘ＝０．１０样品为铁磁性的ｂ．ｃ．ｃ结构马氏体相与顺磁性的ｆ．ｃ．ｃ结构奥氏体相共存；当ｘ＝０．２５～０．３０，样品中只单独存在ｆ．ｃ．ｃ结构的顺磁相；ｘ≥０．５０时，样品为ｆ．ｃ．ｃ．结构的顺磁相和铁磁相共存。顺磁相被认为是反铁磁相温度超过Ｎｅｅｌ点形成的。磁性随ｘ的变化趋势与块材基本一致     

钙钛矿锰氧化物Pr1-xCaxMnO3(0.3≤x≤0.5)的结构和磁性研究

通过固相反应法合成了Pr1-xCaxMnO3(x＝0.3,0.4,0.5)系列多晶样品,对样品的结构和磁性进行了研究.XRD检测结果发现,样品均为单相,空间群为Pbnm.用超导量子磁强计(SQUID)对样品的磁性进行了研究,着重分析了掺杂浓度为x＝0.4的Pr0.6Ca0.4MnO3样品.从测得的M-T曲线可知,在降温过程中,样品经历了电荷有序转变和反铁磁转变,电荷有序温度TCO=250K,反铁磁转变温度TN=170K.通过不同温度的M-H曲线,证实了样品在各个阶段的磁有序转变.     

铜-锌-铝系低温变换催化剂氢还原动力学的研究

常压下用直流法微型反应器对国产铜－锌－铝系低温变换催化剂进行了氢还原动力 学的研究。其还原历程与纯氧化铜不同，在４４３Ｋ以上没有诱导期．在 ｒ－ι图或 ｒ－α 图上出现了两个峰。主峰所对应的还原度基本上与反应温度和氢浓度无关。在４４３－ ４８３Ｋ，ＰＨ２＝４４５８－１１１４５Ｎ／ｍ２范围内，在还原度大于２０％以上的过程，可用 一个统一的动力学方程描述：     

YBa_（2－x）Pr_xCu_3O_（7－8）的磁取向粉末样品的~（63）Cu

本文报道了ＹＢａ２－ｘＰｒｘＣｕ３Ｏ７－８（ｘ＝０．０２５－０．１）磁取向粉末样品的变温ＮＭＲ研究。作者详细测量了６３Ｃｕ的Ｋｎｉｇｈｔ位移Ｋ和自旋－晶格驰豫率１／Ｔ２的变温规律。随着Ｐｒ的掺进，Ｃｕ（１）Ｃｕ（２）位的Ｋｎｉｇｈｔ位移开始依赖于温度，Ｋｎｉｇｈｔ位移的轨道贡献和各向异性超精细作用基本保持不变。在我们测量温区内（７７－３００Ｋ），１／Ｔ１随掺杂浓度增加而有所增强，这与反铁磁相关自旋涨落图象一致。我们用ＭＭＰ理论进行了详细分析。     

La0.85Te0.15MnO3的电磁输运性质及其内耗的研究

研究了La0.85Te0.15MnO3的电磁输运行为及其内耗。其磁化强度随温度的变化曲线经历了一个从顺磁到铁磁的转变,其电阻率随温度变化曲线出现了2个转变峰,其中高温峰在居里温度TC对应于顺磁到铁磁的磁转变。在金属到绝缘转变区域出现了内耗峰,并且模量也出现了变化。     

钙钛矿锰氧化物Nd_(0.5)Sr_(0.3)Ba_(0.2)MnO_3多晶的磁性和相分离

通过固相反应法合成Nd0.5Sr0.3Ba0.2MnO3多晶样品,采用粉末X射线衍射(XRD)、超导量子磁强计(SQUID)和电子自旋共振谱仪(ESR),对样品的结构和磁性进行了研究.XRD检测结果表明,样品为单相,空间群为Pbnm.磁性测量和ESR结果表明,在降温过程中,样品经历了铁磁有序转变(TC=250K)、电荷有序转变(TCO=190K)和反铁磁转变(TN=120K).通过ESR谱线的参数随温度的变化可以观察到各个磁有序转变温度,TN相似文献   

Magnetic order close to superconductivity in the iron-based layered LaO1-xFxFeAs systems

Following the discovery of long-range antiferromagnetic order in the parent compounds of high-transition-temperature (high-T(c)) copper oxides, there have been efforts to understand the role of magnetism in the superconductivity that occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds. Superconductivity in the newly discovered rare-earth iron-based oxide systems ROFeAs (R, rare-earth metal) also arises from either electron or hole doping of their non-superconducting parent compounds. The parent material LaOFeAs is metallic but shows anomalies near 150 K in both resistivity and d.c. magnetic susceptibility. Although optical conductivity and theoretical calculations suggest that LaOFeAs exhibits a spin-density-wave (SDW) instability that is suppressed by doping with electrons to induce superconductivity, there has been no direct evidence of SDW order. Here we report neutron-scattering experiments that demonstrate that LaOFeAs undergoes an abrupt structural distortion below 155 K, changing the symmetry from tetragonal (space group P4/nmm) to monoclinic (space group P112/n) at low temperatures, and then, at approximately 137 K, develops long-range SDW-type antiferromagnetic order with a small moment but simple magnetic structure. Doping the system with fluorine suppresses both the magnetic order and the structural distortion in favour of superconductivity. Therefore, like high-T(c) copper oxides, the superconducting regime in these iron-based materials occurs in close proximity to a long-range-ordered antiferromagnetic ground state.     

Molecular dynamics simulations on specific heat capacity and glass transition temperature of liquid silver

The embedded-atom method is adopted to simulate the specific heat capacity of liquid silver. The relationship between the specific heat capacity and the temperature above and below melting point is derived. The results show that there exists an anormaly of the specific heat capacity of liquid silver near 950 K. Simulated pair distribution functions show that the liquid-to-glass transition takes place at this temperature.     

含阻挫和各向异性的反铁磁自旋链的键算符理论

基于键算符平均场近似,讨论了阻挫和单粒子各向异性对自旋为1的反铁磁自旋链的影响。通过求解自恰方程,得到了低能激发能谱、自由能、静态磁化率和比热容。系统激发态能谱的能隙分别在阻挫和单粒子各向异性的影响下转变为0,这意味着存在量子相变。阻挫诱导的临界点是在$\alpha $为1.39和D为−0.35,$ \mathrm{\alpha } $是相邻格点之间的阻挫比值,D是沿z轴方向的各向异性因子。计算的相变临界点与其他数值方法的结果是一致的。     

Hidden orbital order in the heavy fermion metal URu(2)Si(2)

When matter is cooled from high temperatures, collective instabilities develop among its constituent particles that lead to new kinds of order. An anomaly in the specific heat is a classic signature of this phenomenon. Usually the associated order is easily identified, but sometimes its nature remains elusive. The heavy fermion metal URu(2)Si(2) is one such example, where the order responsible for the sharp specific heat anomaly at T(0) = 17 K has remained unidentified despite more than seventeen years of effort. In URu(2)Si(2), the coexistence of large electron electron repulsion and antiferromagnetic fluctuations leads to an almost incompressible heavy electron fluid, where anisotropically paired quasiparticle states are energetically favoured. Here we develop a proposal for the nature of the hidden order in URu(2)Si(2). We show that incommensurate orbital antiferromagnetism, associated with circulating currents between the uranium ions, can account for the local fields and entropy loss observed at the 17 K transition. We make detailed predictions for the outcome of neutron scattering measurements based on this proposal, so that it can be tested experimentally.     

Spin correlations in the electron-doped high-transition-temperature superconductor Nd2-xCexCuO4+/-delta

High-transition-temperature (high-T(c)) superconductivity develops near antiferromagnetic phases, and it is possible that magnetic excitations contribute to the superconducting pairing mechanism. To assess the role of antiferromagnetism, it is essential to understand the doping and temperature dependence of the two-dimensional antiferromagnetic spin correlations. The phase diagram is asymmetric with respect to electron and hole doping, and for the comparatively less-studied electron-doped materials, the antiferromagnetic phase extends much further with doping and appears to overlap with the superconducting phase. The archetypal electron-doped compound Nd2-xCexCuO4+/-delta (NCCO) shows bulk superconductivity above x approximately 0.13 (refs 3, 4), while evidence for antiferromagnetic order has been found up to x approximately 0.17 (refs 2, 5, 6). Here we report inelastic magnetic neutron-scattering measurements that point to the distinct possibility that genuine long-range antiferromagnetism and superconductivity do not coexist. The data reveal a magnetic quantum critical point where superconductivity first appears, consistent with an exotic quantum phase transition between the two phases. We also demonstrate that the pseudogap phenomenon in the electron-doped materials, which is associated with pronounced charge anomalies, arises from a build-up of spin correlations, in agreement with recent theoretical proposals.     

电荷有序态La0.25Ca0.75MnO3的红外光学特性分析

采用高温固相法制备了电荷有序态锰氧化物La0.25Ca0.75MnO3样品.从297？78K每隔10K测试了该样品的变温红外反射谱,发现在240K时红外反射谱有了显著的转变.这与该样品的磁化强度-温度关系曲线所呈现的相变温度点相一致.磁性测量表明该样品在240K发生了高温顺磁相到低温反铁磁相的转变.此外,红外光电导还揭示了该样品中在160K温度处有新的反常现象,可能是在此温度附近存在低能激发态.从反铁磁转变、电荷有序态和晶格畸变等方面对观察到的实验结果进行了分析和讨论.     

Novel multiferroicity in orthorhombic SmCrO3

This paper reports the ferroelectricity in antiferromagnetic SmCrO_3 with a reasonably large value of spontaneous electric polarization(70μC/cm~2mC cm~(-2)at 50 K)based on the measurement of pyroelectric current.The experimental results showed that the temperature of the onset of polar order was evidently higher(about220 K)than the Neel temperature(T_N=197 K)in the magnetodielectric studies.The calculated magnetodielectric effect(MDE)value was explicitly negative with maximum|MDE|values of about 3.6%around 230 K.The absence of a convincing signature in MDE at antiferromagnetic ordering temperature T_Nindicated the absence of magnetoelectric coupling around this temperature regime.The results further confirmed that the onset of polar order can be attributed to the structural distortion,rather than the canted noncollinear magnetic structure.     

Electronic structure of the iron-based superconductor LaOFeP

The recent discovery of superconductivity in the iron oxypnictide family of compounds has generated intense interest. The layered crystal structure with transition-metal ions in planar square-lattice form and the discovery of spin-density-wave order near 130 K (refs 10, 11) seem to hint at a strong similarity with the copper oxide superconductors. An important current issue is the nature of the ground state of the parent compounds. Two distinct classes of theories, distinguished by the underlying band structure, have been put forward: a local-moment antiferromagnetic ground state in the strong-coupling approach, and an itinerant ground state in the weak-coupling approach. The first approach stresses on-site correlations, proximity to a Mott-insulating state and, thus, the resemblance to the high-transition-temperature copper oxides, whereas the second approach emphasizes the itinerant-electron physics and the interplay between the competing ferromagnetic and antiferromagnetic fluctuations. The debate over the two approaches is partly due to the lack of conclusive experimental information on the electronic structures. Here we report angle-resolved photoemission spectroscopy (ARPES) of LaOFeP (superconducting transition temperature, T(c) = 5.9 K), the first-reported iron-based superconductor. Our results favour the itinerant ground state, albeit with band renormalization. In addition, our data reveal important differences between these and copper-based superconductors.     

Thermodynamic properties of the charge-density-wave transition in potasium blue brone

Thermodynamic properties of the charge-density-wave (CDW) transition in potassium blue bronze K_0.3MoO₃ are investigated by the measurement of specific heat. A second-order phase transition is observed at 177.5 K. The specific heat jump, and enthalpy and entropy changes associated with the transition are estimated. The results suggest that the lattice plays an important role in thermodynamics for this compound. Analysis of the data near CDW transition shows that width of critical region is about 6 K and the critical behavior belongs to the universality class of the three-dimensional XY model. Supported by the National Nature Science Foundation of China & Youth Foundation of Science of Shanghai Shi Jing: born in Mar. 1956, Accociate professor