Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5

We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y₂BaNi_1-xZn_xO₅. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature. We obtain a Curie-Weiss susceptibility χ( T ) ∼ C /(Θ + T ) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order. We explain how to obtain the “impurity” susceptibility ( T ) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental data are well fitted by T ( T ) = C _imp 1 + T _imp / T . In the temperature range [100 mK, 1 K] the experimental data are well fitted by T ( T ) = A ln( T / T _c ), where T _c increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments. We also obtain a maximum in the temperature dependence of the ac-susceptibility ( T ) which suggests the existence of antiferromagnetic correlations at very low temperature. Received 17 July 2001     

Effects of pH and citric acid contents on characteristics of ester-derived BaFe12O19 powder

The single domain size of BaFe₁₂O₁₉ powder with crystallite sizes less than 200 nm was produced using a citric acid precursor method. Fe³⁺ and Ba²⁺, in a molar ratio of 12, were chelated by COOH⁻ in an aqueous solution. After ethylene glycol additions, esterification, dehydration, and calcination led to the formation of ester-derived BaFe₁₂O₁₉ powder. High pH and/or high citric acid contents in the starting solution are required to complete chelate metallic ions in the solution and to form pure barium ferrite powder at 1073 K. Pure single magnetic domain BaFe₁₂O₁₉ particles of M(30 kOe)≈54 emu/g, M_r≈28 emu/g, and H_c≈3.7 kOe were produced using [citric acid]/[metallic ions]=1.5 and pH7.     

Direct measurement of the magnetocaloric effect in La0.67Ca0.33MnO3

Polycrystalline perovskite La_0.67Ca_0.33MnO₃ was synthesized by a sol–gel method. Its adiabatic temperature change ΔT_ad induced by a magnetic field change was measured directly. At 268 K, near its Curie temperature T_C, ΔT_ad of La_0.67Ca_0.33MnO₃ induced by a magnetic field change of 2.02 T reaches 2.4 K. The latent heat Q and magnetic entropy change −ΔS_M induced by a magnetic field change were calculated from the temperature dependence of ΔT_ad and zero-field heat capacity C_p. The maximum values of Q and −ΔS_M in La_0.67Ca_0.33MnO₃ induced by a magnetic field change of 2.02 T are 1.85 J g⁻¹ and 6.9 J kg⁻¹ K⁻¹, respectively. The former is larger than the phase transition latent heat of heating or cooling, which is about 1.70 J g⁻¹.     

Influence of chemistry and hot rolling conditions on high permeability non-grain oriented silicon steel

This paper discusses the influence of chemical composition on the final electromagnetic properties in higher permeability material. Furthermore, the effect of the hot rolling practice and the end of austenite transformation temperature range on the hot band microstructure is described. The magnetic polarization J₅₀₀₀ better than 1.7 T, using hot rolling conditions 40 mm transfer bar thickness, finish mill entry temperature 1000 °C, and finishing temperature 800–840 °C and after decarburization heat treatment and grain growth treatment, was obtained.     

Topological order in the phase diagram for high-temperature superconductors with point defects

Applying a Lindemann like criterion obtained previously by Kierfeld et al. [J. Kierfeld, T. Nattermann, T. Hwa, Phys. Rev. B 55 (1997) 626], we estimate the magnetic field and temperature for a high-T_c superconductor, at which a topologically ordered vortex glass phase becomes unstable with respect to a disorder-induced formation of dislocations. The employed criterion is shown to be equivalent to a conventional phenomenological Lindemann criterion including the values for the numerical factors, i.e., for the Lindemann number. The positional correlation length of the topologically ordered vortex glass is calculated.     

Strukturelle Charakterisierung der Dicyanamid-Komplexe von Kupfer(II), Nickel(II) bzw. Kobalt(II) mit Aminopyridinen

Summary New dicyanamide complexes of the typeM[N(CN)₂]₂ L ₂ (M=Cu or Ni;L=2-, 3-, 4-aminopyridine, 2-amino-5-nitropyridine) and Co[N(CN)₂]₂ (2-amino-5-nitropyridine)₂ were prepared and studied by spectroscopic methods as well as by room-temperature magnetic moments. The results show that the Cu(II) complexes have elongated pseudooctahedral structures while the Ni(II) and Co(II) complexes are octahedral. In most cases the N(CN)₂ groups are in bridging function and through their cyanide nitrogens, or-more rarely-amide and cyanide nitrogens connect the basic structure units into polymeric conglomerates. In the Cu(II) systems exchange coupling is seen from the _eff value or ESR spectrum.

Professor Viktor Gutmann zum 70. Geburtstag gewidmet     

Surface properties of finite classical Coulomb systems: Debye-Hückel approximation and computer simulations

We report analytical and numerical studies of surface correlations in finite, homogeneously polarizable, classical Coulomb systems placed in an insulating or conducting environment. Their purpose is to understand the phenomenological, shape-dependent laws of electrostatics, from the point of view of statistical mechanics; we focus on the knowledge of the dielectric susceptibility of the system, a quantity proportional to the equilibrium fluctuation of the system's instantaneous polarization per unit volume. This goal has been achieved for a system in a conducting state. The picture is that the shape-dependent part of the susceptibilities results from the action of unbounded observables (the second moments of the instantaneous polarization of the system) on long-range surface correlations and that the relations of electrostatics are verified by means of shape-dependent thermodynamic limits. This picture is supported (i) by exact solutions and asymptotic analysis of the Debye-Hückel approximation of multicomponent plasmas in disks and spheres with insulating and conducting environment and also in ellipses in a vacuum, and (ii) by computer simulations of a one-component plasma in a disk with different environments, notably a conducting environment with permeable and impermeable wall. These observations have revealed for the first time the reason why the susceptibility of a conducting disk in a conductor with impermeable walls diverges linearly with the radius of the disk: this is due to the occurrence of long-range radial correlations in the conductor. These findings are quantitatively interpreted in terms of a novel canonical Debye-Huckel approximation as contrasted to the ordinary grand canonical version. Lastly a fresh look at the problem of the surface correlations of a conductor in a vacuum, which places the observer close to the surface of the conductor but in the vacuum, is presented and applied to the disk, the ellipse, the cylinder, the sphere, and the wedge.     

Synthesis and crystal structure of a new one-dimensional system with end-to-end single dicyanamide bridges between nickel(II) centres

The complex [Ni(tn)₂{N(CN)₂}]ClO₄ (tn=trimethylenediamine) has been synthesized and the structure has been determined. The complex forms a one-dimensional chain structure via the bidentate bridging ligand dicyanamide. A two-dimensional networks is formed via interchain hydrogen bond interactions.     

Recyclable,non-leaching antimicrobial magnetic nanoparticles

Recyclable antimicrobial magnetic nanoparticles, Fe₃O₄@P(St-co-AcQAC), were prepared through surfactantfree seeded emulsion polymerization involving a polymerizable, hydrophobic quaternary ammonium compound (QAC). These antimicrobial magnetic nanoparticles demonstrated excellent antimicrobial activities against both Grampositive and Gram-negative bacteria, and can be reused for multiple times.     

化学发光磁酶免疫法检测O157∶H7大肠埃希菌

O157∶H7大肠埃希菌是一种致病力非常强的微生物.近年来,陆续有其引起食物中毒事件的报道.1996年日本发生O157∶H7大肠埃希菌食物中毒的爆发流行,感染病例逾万人,死亡9例.2001年我国江苏及安徽等地也发生了肠出血性O157∶H7大肠埃希菌所引发的感染性腹泻事件.目前O157∶H7大肠埃希菌实验室常规检测方法为分离培养计数法,此法费时费力,需要几天的时间才能得到检测结果[1,2],缺乏应对突发事件的能力,因此亟需开发快速检测技术.近年来,多种微生物快速检测技术如ELISA法[3]、热解质谱测定法[4]、多聚酶链反应[5]、荧光成像技术[6]、生物发…