Magnetization and Current Noise in Hg-1201 And Tl-1223

Magnetization and current noise measurements are reported in Hg-1201 and a substituted Tl-1223 system. The temperature behaviour of the voltage noise in Hg-1201 is similar to YBCO, with large peaks at the weak-link transition. In Tl-1223, a original two peak noise specrum at fields of 250G is observed, not explained by percolative models.     

High Pressure Synthesis and Properties of Hg-1234 and Hg-1223 Phases.

The Hg-1223 and Hg-1234 phases were synthesized using the program-controlled high pressure chamber. The variation of the oxygen content in the starting oxides mixture HgBa₂Ca₃Cu₄O_x, performed by changing BaO/BaO₂ and Cu₂O/CuO ratios influences significantly the phase formation. Dependence of T_c vs. a-parameter for HgBa₂Ca₂Cu₃O₈₊ superconductor has a cupola-shaped character, as it was found for the lower members of the homologous series.     

A Significant Drop in Resistance Around 200 K in Superconducting Hg-1223 and Discussion

Tholence et al. and Yao et al. observed a significant drop in resistance around 250 K and 230 K respectively on superconducting Hg-based compounds. Yao et al. believed that this drop in resistance is due to the presence of the free-state liquid mercury or Hg-Au alloys in the sample. We report here the electrical resistivity measurements on single phase (as determined by X-ray powder technique) Hg-1223, which has shown a partial or total drop in resistivity around 200 K but with no significant observation of diamagnetic signal. On the other hand, an internal friction peak around 203 K was observed in our internal friction experiment. We are sure that the drop in resistance for our Hg-1223 sample around 200 K is not due to the presence of liquid mercury or Hg–Au alloys in the sample since we did not use the gold foil or silver foil to enwrap our sample. We rather believe that the drop in resistivity is due to superconductivity or other mechanisms.     

Thermopower of non-superconducting and superconducing Nd1·85Ce0·15CuO4−y samples

The thermopower of single-phase samples of Nd_1·85Ce_0·15CuO_4−y was measured from 250 K down to 10 K. The as-prepared sample was not superconducting. It had a negative thermopower at 250 K, whose magnitude increased as temperature was decreased to 95 K. A further reduction in temperature caused a decrease in magnitude of thermopower. The sign of the thermopower changes to positive at 12 K. The superconducting sample also showed the same behaviour but the change of sign now occurred at 40 K. Below 40 K, the thermopower showed a positive peak and reduced to zero at the superconducting transition. These results were compared with previous studies.     

纳米晶Sr-Cr水合石榴石的水热合成与磁性研究

在相对温和的水热体系里合成出纳米品Sr－Cr水合石榴石，采用XRD、IR和XPS光谱图对产物进行了表征．结果表明，高溶解性的初始物和高浓度的矿化剂大大降低其晶化温度，并提高其结晶度．随温度升高，出现Sr十二面体最近邻的OH-断裂与分解过程，在空气或氧气中，还出现了Cr（Ⅲ）到Cr（Ⅳ）氧化过程．骨架离子Cr（Ⅲ）的价态变化直接决定着水合石榴石的分解过程及其产物的结构类型,低温磁化率测量表明Sr3Cr2（OH）12是顺磁性的；在该结构中出现了轨道角动量的完全猝灭．该结构中存在较高对称性的Cr－OH八面体．     

纳米晶Sr-Cr水合石榴石的水热合成与磁性研究

在相对温和的水热体系旦合成出纳米晶Ｓｒ－Ｃｒ水合石榴石，采用ＸＲＤ、ＩＲ和ＸＰＳ光谱图对产物进行了表征。结果表明，高溶解性的初始物和高浓度的矿化剂大大降低其晶化温度，并提高其结晶度。随温度升高，出现Ｓｒ十二面体最近邻的ＯＨ＾－断裂与分解过程。在空气或氧气中，不出现了Ｃｒ（Ⅲ）到Ｃｒ（Ⅳ）氧化过程。骨架离子Ｃｒ（Ⅲ）的价态变化直接决定着水合石榴石的分解过程及其产物的结构类型。低温磁化率测量表明Ｓｒ３     

Magnetic Properties of Several Transition Metal Silicomolybdates with a Magnetic Pyrochlore Lattice

We describe the low-temperature magnetic susceptibilities of M₂²⁺SiO₄[MoO₃]₁₂×30H₂O, with M = Mn, Co, Fe, and Ni. Magnetic order is visible in Mn₂SiO₄[MoO₃]₁₂×30H₂O, possibly due at least in part to the magnetic dipole–dipole interaction, and magnetic frustration is suggested by the behavior of Co₂SiO₄[MoO₃]₁₂×30H₂O and Ni₂SiO₄[MoO₃]₁₂×30H₂O. Fe₂SiO₄[MoO₃]₁₂×30H₂O exhibits a nonmagnetic ground state, with a very small splitting between the ground and first excited states of Fe²⁺.      

Synthesis and Properties of Magnetic Nanoparticles

The uniform mesoporous SBA-15 consisting of SiO2 with long-range channels Offers an excellent host material to synthesize or assemble the magnetic nanocomposites, such as Fe, Ni. In this paper, highly dispersed and uniform iron nanoparticles were incorporated into the pore channels of SBA-15 through a newly developed strategy in which some kinds of coupling agents were used to entrap the nanoparticles into the silica framework. The X-ray diffraction （XRD）, fourier transmission infrared spectroscopy （FTIR）, high-resolution transmission electronic microscopy （HRTEM） and energy dispersive X-ray spectroscopy （EDX） were performed to further identify the successful incorporation and grafting of iron. Compared with other ordinary non-assembled magnetic nanoparticles, the assembled Fe nanoparticles with the diameter even in the size range of 5～6 nm still have better magnetic properties.     

Thermopower of Carbon Nanotubes in a Magnetic Field

Abstract

The thermopower of a quantum nanotube in magnetic field was investigated. We obtained the convenient analytic formula for the thermopower. The temperature dependence of the thermopower is studied and the influence of the magnetic field on the thermopower is examined. Oscillations in the thermopower were investigated.     

Phase Transformations of Cobalt Oxides in CoxOy–ZnO Multipod Nanostructures via Combustion from Thermopower Waves

The study of combustion at the interfaces of materials and chemical fuels has led to developments in diverse fields such as materials chemistry and energy conversion. Recently, it has been suggested that thermopower waves can utilize chemical‐thermal‐electrical‐energy conversion in hybrid structures comprising nanomaterials and combustible fuels to produce enhanced combustion waves with concomitant voltage generation. In this study, this is the first time that the direct phase transformation of Co‐doped ZnO via instant combustion waves and its applications to thermopower waves is presented. It is demonstrated that the chemical combustion waves at the surfaces of Co₃O₄–ZnO multipod nanostructures (deep brown in color) enable direct phase transformations to newly formed CoO–ZnO_1−x nanoparticles (olive green in color). The oxygen molecules are released from Co₃O₄–ZnO to CoO–ZnO_1−x under high‐temperature conditions in the reaction front regime in combustion, whereas the CoO–ZnO multipod nanoparticles do not undergo any transformations and thus do not experience any color change. This oxygen‐release mechanism is applicable to thermopower waves, enhances the self‐propagating combustion velocity, and forms lattice defects that interrupt the charge‐carrier movements inside the nanostructures. The chemical transformation and corresponding energy transport observed in this study can contribute to diverse potential applications, including direct‐combustion synthesis and energy conversion.     

Synthesis and Magnetic Properties of Ni-Zirconia Composites

A novel method has been developed for the fabrication of composite magnetic films on various conductive substrates. Cathodic electrolytic deposition was used as the technique to obtain thin films from solutions of nickel and zirconium salts. The hydroxide deposits were converted to Ni-ZrO₂composites after sintering in reducing conditions. Deposit yield was studied in the constant current deposition mode. Deposits were evaluated using X-ray analysis and magnetic measurements. Results of dc and ac measurements performed in different magnetic fields, temperatures, and frequencies demonstrated the magnetic properties of the composites.     

CeVO_4纳米棒的合成及其磁性能研究

以Na2EDTA为模板导向剂,利用水热法成功合成了单晶CeVO4纳米棒.使用X射线衍射仪(XRD)、透射电镜(TEM)、高分辨透射电镜(HRTEM)和超导量子磁强计(SQUID)等对产物的结构和磁学性能进行了表征.结果表明.产物为CeVO4纳米棒,其长度为600nm左右,直径为80nm左右.研究发现,模板剂Na2EDTA和生长溶液的pH值决定着CeVO4纳米晶体的形貌与生长机制.进一步对CeVO4纳米棒的磁性进行研究,表明在低温下,由于受到CeVO4纳米晶体的尺寸效应和Ce离子4f电子的影响,CeVO4纳米晶体表现出明显的超顺磁性,而强烈的一维各向异性和Eu3+掺杂则显著提高了CeVO4纳米棒的磁性能.     

砝码磁性测量过程中几何形状修正因子的计算与影响

通过一系列实验和数据,讨论用磁化率计法测量砝码磁性时各测量分量对砝码磁化率测量结果的影响,并着重分析了砝码几何形状修正因子的测量与确定,比较不同测量方式的特点,以求减少砝码磁性测量时的误差。     

Fe3O4十八面体和十二面体的合成及磁性能

在水热合成α-Fe2O3十八面体和十二面体的基础上,以5%H2+95%N2为还原介质,通过控制还原条件制备出纯相Fe3O4十八面体和十二面体颗粒.用X射线衍射、扫描电镜、X射线光电子能谱、透射电镜和振动样品磁强计等手段对样品进行了表征.结果表明,颗粒表面氟离子吸附层的存在是其形貌保持较好的重要原因.与其它形貌的Fe3O...     

Synthesis,Structural, and Magnetic Properties of Nanocrystalline Ti 0.95Co0.05O2-Diluted Magnetic Semiconductors

With a view to investigate the influence of nanometric size on the structural, surface, and magnetic properties of nanocrystalline Ti_0.95Co_0.05O₂-diluted magnetic semiconductors, prepared by a novel simple controllable peroxide-assisted reflux chemical route followed by annealing at different temperatures, a systematic investigation has been undertaken. Structural characterizations such as X-ray diffraction followed by Rietveld refinement, electron diffraction pattern, Fourier transform infrared, Raman scattering, and X-ray photoelectron spectroscopy (XPS) measurements have shown anatase phase formation in nanocrystalline Ti_0.95Co_0.05O₂ without any additional impurity phases. The modified reflux chemical route was effective in obtaining pure phase Ti_0.95Co_0.05O₂ nanoparticles. Surface morphological investigations by using transmission electron microscopy and atomic force microscopy measurements showed the predominant effect of random distribution of nanoparticles on the aggregation behavior and local microstructural changes. The deconvoluted XPS core level Co 2p spectral study manifested the oxidation state of Co as + 2 and is found to be stable with varying particle size and annealing temperature. The ferromagnetic behavior was investigated by vibrating sample magnetometer, magnetic force microscopy, and electron spin resonance measurements. These magnetization studies showed all the samples are ferromagnetic at room temperature without any magnetic clusters. The correlation between structure, surface condition of the nanoparticles and local electronic interactions, and magnetization of the samples was analyzed and explored the origin of ferromagnetism.     

High Pressure Synthesis and Properties of HgBa2Ca4Cu5O y (Hg-1245) Superconductor

We have synthesized an almost single phase sample of HgBa₂Ca₄Cu₅O _y with T _c of 108K using a high pressure and high temperature technique. The carreier concentration, N _H, was deduced from the Hall coefficient R _H using a simple relation (N _H=1/(eR _H)) at 300 K and the Hall number per CuO₂ plane was estimated to be 0.12 for this sample. We also observed a T ² dependence of the Hall angle (cot _H). The critical current density (J _c) and irreversible field (Birr) have been estimated from measurements of magnetic hysteresis loops assuming Bean's critical state model. The Birr for this sample as a function of temperature was lower than HgBa₂Ca₂Cu₃O _y (Hg-1223). This result suggests that the anisotropy in Hg-1245 is seem to be larger than that in Hg-1223 and inter-layer coupling among five CuO₂ planes in Hg-1245 becomes weaker than that in Hg-1223 by adding two CuO₂ planes.     

Giant Peak Voltage of Thermopower Waves Driven by the Chemical Potential Gradient of Single‐Crystalline Bi2Te3

The self‐propagating exothermic chemical reaction with transient thermovoltage, known as the thermopower wave, has received considerable attention recently. A greater peak voltage and specific power are still demanded, and materials with greater Seebeck coefficients have been previously investigated. However, this study employs an alternative mechanism of transient chemical potential gradient providing an unprecedentedly high peak voltage (maximum: 8 V; average: 2.3 V) and volume‐specific power (maximum: 0.11 W mm^?3; average: 0.04 W mm^?3) using n‐type single‐crystalline Bi₂Te₃ substrates. A mixture of nitrocellulose and sodium azide is used as a fuel, and ultraviolet photoelectron spectroscopy reveals a significant downshift in Fermi energy (≈5.09 eV) of the substrate by p‐doping of the fuel. The induced electrical potential by thermopower waves has two distinct sources: the Seebeck effect and the transient chemical potential gradient. Surprisingly, the Seebeck effect contribution is less than 2.5% (≈201 mV) of the maximum peak voltage. The right combination of substrate, fuel doping, and anisotropic substrate geometry results in an order of magnitude greater transient chemical potential gradient (≈5.09 eV) upon rapid removal of fuel by exothermic chemical reaction propagation. The role of fuel doping and chemical potential gradient can be viewed as a key mechanism for enhanced heat to electric conversion performance.