The impact of nuclear magnetism on superconductivity

The influence of nuclear magnetism on the superconducting critical field B_c has been measured in the nuclear magnets Al, AuIn₂, and Sn, at ultralow temperatures, 17 μKT1 K. The materials have been chosen in respect to their distinctive Korringa constants κ(Al, AuIn₂, Sn)=(1.8, 0.1, 0.05) Ks. Both in the weakly and in the strongly coupled nuclear magnets, Al and Sn, a reduction of B_c is observed being proportional to the nuclear magnetization at T4 mK. However, using the high resolution of the experiment performed on Sn, the decrease of B_c at cooling down to 70 μK is found to be nonmonotonic. The features of the recently measured B_c(T) curve of Sn which are not understood yet as well as the formerly observed results of the interplay of nuclear ferromagnetism and superconductivity in AuIn₂ have motivated ongoing experiments which try to clear up the pair breaking contribution of nuclear magnetism.     

Syntheses, structures, magnetism, and optical properties of gadolinium scandium chalcogenides

Three gadolinium scandium chalcogenides have been synthesized using Sb₂Q₃ (Q=S, Se) fluxes at 975 °C. Gd_3.04Sc_0.96S₆, GdScS₃, and Gd_1.05Sc_0.95Se₃ are crystallized in U₃ScS₆ type, GdFeO₃ type, and UFeS₃ type structures, respectively. The magnetic susceptibilities for these compounds follow the Curie-Weiss law above their transition temperatures. The effective magnetic moments are close to calculated values for free Gd³⁺ ions. The Weiss constants for Gd_3.04Sc_0.96S₆, GdScS₃, and Gd_1.05Sc_0.95Se₃ are determined to be −3.3(1), −4.5(4), and 1.5(1) K, respectively. Gd_3.04Sc_0.96S₆ orders antiferromagnetically below 9 K. GdScS₃ exhibits an antiferromagnetic ordering below 3 K with a weak ferromagnetism. Gd_1.05Sc_0.95Se₃ undergoes a ferromagnetic transition around 5 K. The optical band gaps for Gd_3.04Sc_0.96S₆, GdScS₃, and Gd_1.05Sc_0.95Se₃ are 1.5, 2.1, and 1.2 eV, respectively.     

Effects of Hole-Doping on Superconducting Properties in MgCNi3 and its Relation to Magnetism

Low temperature Mössbauer experiments were performed in Fe-doped and in C-deficiency MgCNi₃. No magnetic moment was found for Fe in MgC(Ni_0.99Fe_0.01)₃ sample and no magnetic hf field was observed at any temperature for all the samples. These results shown no evidence of magnetic fluctuation or magnetic ordering influencing the depress of superconductivity in hole-doped MgCNi₃.     

μ+SR study of heavy-fermion magnetism in Ce(Cu1-xNix)2Ge2

We report muon spin relaxation (μ⁺SR) studies on the magnetic phase diagram of Ce(Cu_1-xNi_x)₂Ge₂ polycrystals for 0.5≤ x ≤ 0.8. A sharp magnetic transition, evidenced by the appearance of a fast Gaussian relaxation component σ, has been observed in the x = 0.5 alloy at 4.0 K in zero applied field. The average local field < B_μ> at the stopping sites of the muons, extracted from σ, exhibits a linear temperature dependence. We associate these features with an incommensurate spin density wave (SDW) ordering. Magnetic ordering, either long range or short range, and signatures of non-Fermi liquid behaviour have not been observed down to 2.0 K at x = 0.8. This revised version was published online in August 2006 with corrections to the Cover Date.     

A structural observation for linear material laws in classical mathematical physics

A class of linear material laws is considered, which covers a number of diverse initial boundary‐value problems of classical mathematical physics. The claim that this class is indeed to a large extent sufficiently general is exemplified for a number of specific models from classical physics. Copyright © 2009 John Wiley & Sons, Ltd.     

Heusler合金Co2TiSn的磁性与输运性能

通过对Heusler合金Co₂TiSn磁性和输运性能的实验研究，发现低场中Co_{2< /sub>TiSn呈现出亚铁磁性；电阻和霍尔电阻率在温度低于8K时均出现异常.同时分析了电输 运的散射机制，并对反常霍尔效应产生的机制进行了探讨. 关键词： Heusler合金 磁性 输运性能}     

Fe2O3/Au/Ag磁性核壳纳米粒子的制备及其SERS研究

本文介绍了一种制备多功能磁性Fe2O3/Au/Ag纳米粒子的简捷方法, 制备的粒子直径大约在100 nm左右, 采用UV-vis和SEM对该结构进行了表征。并通过调节硝酸银的用量, 制备了一系列具有不同壳层厚度和表面结构的多重核壳纳米粒子。以苯硫酚(TP)为探针分子, 研究了不同银壳厚度的磁性纳米粒子的表面增强拉曼散射(SERS)活性。结果表明随Ag:Au比例的不断增加, 其SERS活性呈现先增大后减小的趋势, 这与表面结构的改变有关。     

Magnons versus free spinons in finite quantum frustrated antiferromagnets

We have investigated the validity of doping with a vacancy the J₁–J₃ frustrated Heisenberg model on a finite square lattice as a way to test the existence of fractional spin excitations. Using a generalized t–J₁–J₃ model we have computed the vacancy spectral functions in the self-consistent Born approximation. We have found that by including spiral fluctuations in the magnetic ground state, the spectral functions on finite systems agree very well with the unbiased exact ones. In contrast to the recent proposal that the quasiparticle weight reduction could be a signal of a spinon free excitation in finite systems, we have found strong evidence that such a reduction is due to the existence of spiral fluctuations.     

General refinement strategy for magnetic structures using spherical neutron polarimetry and representation analysis

Spherical neutron polarimetry (SNP) is a powerful technique for the determination of magnetic structures which may otherwise be intractable. The complexity of the neutron scattering process and the large number of different possible trial structures typically leads to refinements based on a simple trial and error generation of possible models and a possible failure to explore valid possible models. The combination of the model symmetry types determined from representational analysis and reverse-Monte Carlo refinement creates a generalized refinement strategy for SNP data that allows refinement in terms of symmetry adapted modes built up from the basis vectors that describe the orientations of the magnetic moments on the different magnetic sites, and those of the different domains that are possible in a sample: spin (S)-domains and K-domains. This methodology typically leads to a large reduction in the number of refined parameters as well as the rigorous inclusion of any symmetry related domains. In combination with reverse-Monte Carlo refinement algorithms a general strategy for refining complex magnetic structures can be created. We present an example of a frustrated magnetic structure that have been determined using this approach Er₂Ti₂O₇.     

MPb10（M=Ti，V，Cr，Cu，Pd）几何结构和磁性的密度泛函计算研究

采用密度泛函理论（density functional theory,DFT）中的广义梯度近似（generalized gradient approximation,GGA）对MPb₁₀（M=Ti,V,Cr,Cu,Pd）四种同分异构体的几何结构和磁性进行了计算研究.发现在四种同分异构体中,D_4d结构的MPb₁₀（M=Ti,V,Cr,Cu,Pd）具有最大的结合 关键词： 几何结构 磁性 密度泛函