The magnetic properties of Fe(OH)2

Ferrous hydroxide free from oxidation was prepared by precipitation from an aqueous solution in an inert gas atmosphere and measured for magnetic susceptibility and magnetization. The antiferromagnetic transition was observed at 34 K, where the susceptibility showed a sharp maximum. The magnetization at 4.2 K increased as the external field increased, and reached 3.6 $\text{μ}{}_{\mathrm{B}}$ per ion at 75 KOe, which is about 90 % of the saturation magnetization of Fe⁺⁺ ion. By analyzing the magnetization curve and the Mössbauer effect, the magnetic structure in an ordered state was deduced as follows: the moments within the layer are arrayed parallel, while those between the adjacent layers antiparallel. The spin easy axis lies in the c-plane. The quadrupole splitting was 3.00 mm/sec at 90 K and showed little temperature dependence between 4.2 K and room temperature. The energy state of Fe⁺⁺ ion in Fe(OH)₂ was specified by the orbital singlet 5A_1g derived from the sign and the magnitude of $\text{1}\text{2}\text{e}{}^2\text{qQ}$. The difference in the magnetic property between Fe(OH)₂ and FeCl₂ was discussed from the energy state of Fe⁺⁺ ion.     

Effect of silica-coating on crystal structure and magnetic properties of metallic nickel particles

The development of a simple method that perfectly controls the oxidation and aggregation of metallic particles has been performed. In the present work, metallic nickel (Ni) particles were used as a control, and silica-coating of them was performed to control oxidation and aggregation of them. Metallic Ni particles with a particle size of 924.1 ± 315.7 nm were synthesized in water and exposed to air. Nickel(II) acetate tetrahydrate, hydrazine, and poly(sodium 4-styrenesulfonate) were used as the Ni source, reducing reagent, and stabilizer, respectively. Silica-coating of the metallic Ni particles was performed by adding tetraethylorthosilicate/(3-aminopropyl)triethoxysilane/ethanol solution to the metallic Ni particle colloid solution (Ni/SiO₂). The uncoated metallic Ni particles and metallic Ni in the Ni/SiO₂ particles began to be oxidized while annealing in air to form NiO at 400 and 500 °C, respectively; the oxidation of metallic Ni particles was controlled by the silica coating. The Ni/SiO₂ particles prepared and annealed at 100–300 °C showed soft magnetic behavior, and the saturation magnetization of g-Ni was almost comparable to that of bulk metallic Ni. In addition, the Ni/SiO₂ particles annealed even at 500 °C still had soft magnetic behavior, which also supported that the oxidation of metallic Ni particles was successfully controlled by the silica coating.     

Surface characterizations of ultrafine Ni particles

Ultrafine Ni particles have been obtained by evaporating pure Ni in methane gas atmosphere of 100 Torr, and in a mixture of H₂ and Ar of 760 Torr, respectively. The distinct characterization of the layers on two kinds of Ni particle surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and oxygen determination. The morphology and mean particle size were determined by transmission electron spectroscopy (TEM) and subsequent image analysis. The structure of ultrafine Ni particles were identified by X-ray diffraction (XRD). The effect of oxide and carbon layers on magnetization of the particles were studied by vibrating sample magnetometer (VSM). It was observed that a carbon-rich and an oxide of Ni₂O₃ layers were formed on the surface of Ni particles obtained in methane gas, and in a mixture of H₂ and A_r gas atmosphere, respectively. It was shown that the methane gas makes resistance to oxidization during evaporating Ni in this gas atmosphere and no nickel carbides or Ni-C solid solutionformed.     

Combustion synthesis of ferromagnetic Al2O3-based cermets in thermal explosion mode

The ferromagnetic Al₂O₃-based cermets with different ratios of Co and Co–50Ni alloys were successfully prepared by combustion synthesis in thermal explosion (TE) mode. The reaction process, microstructure, and magnetic property of cermets were investigated. The relative density of cermets can be over 95% via uniaxial loading at the time of ignition when the cermets are hot and ductile. In Al₂O₃–Co cermets, β-Co and α-Co co-exist at room temperature with average size of less than 10 μm and disperse homogeneously in the matrix, while in Al₂O₃–(Co–50Ni) cermets, the network-like Co–50Ni alloy can infiltrate into the boundary gaps of Al₂O₃ particles. The ferromagnetic Co and Co–50Ni alloys are responsible of the magnetic properties of Al₂O₃-based cermets. The saturation magnetization strongly depends on the magnetic characteristics and ratios of ferromagnetic phases. Al₂O₃–(Co–50Ni) cermets have soft magnetic properties with high magnetic susceptibility and low coercive force.     

High Field Metamagnetism of PrRh2Si2 Single Crystal Compound Having Anomalously High Nèel Temperature

High field magnetization up to 18 T and magnetic susceptibility measurements have been carried out on a PrRh₂Si₂ single crystal. The anomalously high Nèel temperature of 70 K is confirmed. A strong uniaxial magnetic anisotropy with the easy c-axis is evidenced. A sharp metamagnetic transition appears at 16 T in the easy c-axis magnetization process while magnetization in the basal plane is very small and the curve is linear. The saturation moment obtained is 3.1μ _B . Crystalline electric field (CEF) effects have been analyzed to discuss the magnetic behaviors.     

基于组分磁性差异制备ZrO2/Ni功能梯度材料研究

根据不同组分的磁性差异，提出一种在梯度磁场中，采用粉浆浇注法制备铁磁性／非磁性功能梯度材料的方法，并用此方法制备出成分连续变化的ZrO2／Ni功能梯度材料．采用能谱分析仪、光学显微镜和X射线衍射仪对ZrO2／Ni功能梯度材料的成分分布、微观结构和相组成进行了研究．结果表明，在0．5T／m的磁场梯度作用下，浆料中Ni和ZrO2颗粒由于所受磁场作用不同而发生重新排列，形成沿样品厚度方向成分的梯度分布．此外，建立了功能梯度材料成分与颗粒粒度、饱和磁化强度以及磁场梯度之间的定量关系．     

Magnetic-field-induced non-linear effects of Josephson coupled superconductor Bi2Sr2CaCu2O8+δ

The dc current-voltage (I-V) relation along the c-axis of single crystalline Bi₂Sr₂CaCu₂O_8+δ has been measured in magnetic fields parallel and perpendicular to the c-axis. In zero field a clear and sharp jump with large hysteresis in theI-V curve was observed, indicative of the dc-Josephson effect. In magnetic field below a characteristic fieldB ^*≈0.4 T (at T=0 K) parallel to the c-axis the magnetic field suppresses the hysteresis and reduces the critical currentI _c drastically, whereas aboveB ^* theI-V curve becomes broad and featureless behavior. The characteristic field scaleB ^* can be interpreted as an energy scale of the Josephson coupling between superconducting layers in Bi₂Sr₂CaCu₂O_8+δ and is argued with emphasis on the correlation length of pancake vortices in this system.     

合金元素对块体纳米晶Fe3Al材料磁学性能的影响

为了研究合金元素对块体纳米晶Fe3Al材料磁学性能的影响,通过铝热反应熔化法制备了纳米晶Fe3Al以及分别含Ni质量分数10%、Cr质量分数10%、Mn质量分数10%和含Ni质量分数10%-Cu质量分数2%的块体纳米晶Fe3Al.在振动样品磁强计(VSM)上测得合金的磁滞回线,分析其磁性能,采用X射线衍射仪进行结构分析和平均晶粒尺寸计算.结果表明:各样品的磁滞回线呈倾斜状且狭长,磁滞损耗很小;含Ni质量分数10%的样品饱和磁化强度Ms较大,剩余磁化强度Mr和矫顽力Hc较其他样品最小,具有较好的软磁性能;添加合金元素后几种材料的晶粒尺寸变小,磁性能有较大变化,合金元素对纳米晶Fe3Al块体材料的磁性能影响明显.     

Magnetic properties of magnesium-cobalt ferrites synthesized by co-precipitation method

The alternating current (a.c.) low field susceptibility vs temperature, magnetization and⁵⁷Fe Mössbauer effect measurements are reported for the spinel solid solution series Mg _x Co_1?x Fe₂O₄ synthesized by a wet-chemical method before and after high temperature annealing. The observed features for the wet samples, such as the coexistence of paramagnetic doublet and magnetic sextets in Mössbauer spectra and lower saturation magnetization values confirm small particle ferrite behaviour. Especially, Mössbauer spectra of wet samples reveal the presence of superparamagnetic particles which exist simultaneously with ferrimagnetic regions in the materials well supported by a.c. susceptibility data. The high temperature annealing changes the wet-prepared ferrites into the ordered magnetic structure of ceramic ferrites.     

Preparation and electrochemical performance of nano-scale nickel hydroxide with different shapes

Platelet-like, flake-like, and needle-like nano-scale β-Ni(OH)₂ particles were prepared by coordination homogeneous precipitation method in this paper. X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared absorption spectra (IR) were used to characterize the microstructure and morphology of the products. The nano-scale Ni(OH)₂ composite electrodes were prepared by mixing 10 wt.% samples with spherical Ni(OH)₂ to carry out charge-discharge test. The results show that the nano-scale Ni(OH)₂ composite electrodes have higher discharge specific capacity, and the nickel hydroxide nanoneedles show a better adulteration performance than the others.     

Steady-shear magnetorheological response of fluids containing solution-combustion-synthesized Ni-Zn ferrite powder

Magnetically soft nickel-zinc ferrite (Ni_0.5Zn_0.5Fe₂O₄) powder with high saturation magnetization was synthesized by solution combustion route using metal nitrates as precursors and glycine as fuel. The particles were found to have irregular morphology. Three different concentrations of magnetorheological fluids (MRFs) were prepared by dispersing 10, 20 and 40?wt% of these particles in thin silicone oil. The behaviours of the MRFs were studied under steady shear conditions at different applied magnetic field strengths (B). The yield strength (τ_Y) and viscosity (η) of all the MRFs were found to increase with B and particle fill fraction ?, while the response of the MRFs was strongly influenced by the morphology, microstructure and saturation magnetization of the particles. Owing to the low density of the particles, the observed off-state viscosity is high. However, the excellent thermo-oxidative and chemical stabilities of these magnetic oxide particles than metallic magnetic particles make these MRFs dependable for applications in harsh working environments. In addition, the low cost and feasibility of large scale preparation of these magnetic oxides make these MRFs further attractive for industrial applications.     

Microstructure and properties of BN/Ni-Cu composites fabricated by powder technology

Microsize Powders of Ni and Cu were prepared by water atomization technique to fabricate metal matrix composites containing various percentages of nanosized boron nitride particles (1, 2, 3, 4, 5 wt. % of BN in a matrix containing (20 wt. %Ni and 80 wt. %Cu). The prepared mixtures were cold compacted under 400 MPa, and sintered for 2 h at 1000 °C in a controlled atmosphere of 3:2 N₂/H₂ gas mixtures. The microstructure and the chemical composition of the prepared powders as well as the consolidated composites were investigated by X-ray diffraction as well as field emission scanning electron microscope (FESEM) equipped with an energy dispersive spectrometer (EDS). The produced Cu and Ni powders have spheroid shape of size less than 100 microns, but the investigated BN has an equiaxed particle shape and particle size of ～ 500 nm. It has been also observed that BN and Ni particles were homogeneously distributed in the Cu matrix of the present BN/Ni-Cu composites. The density, electrical resistivity, saturation magnetization and hardness of the composites were measured. It was observed that, by increasing BN content, the relative density was decreased, while the saturation magnetization, electrical resistivity and hardness were increased.     

Bulk magnetic properties of Co-Zn ferrites prepared by the co-precipitation method

The alternating current (a.c.) susceptibility versus temperature and magnetization measurements are reported for the disordered spinel ferrite system Zn _x Co_1-x Fe₂ O₄ prepared by a wet chemical method before and after high temperature annealing. The low field a.c. susceptibility measurements indicate that the low temperature synthesis of wet prepared Co-Zn ferrites aids the formation of spin-clusters and thereby increases the magnetic inhomogeneity. The X-ray analysis shows that the samples are single phase spinels and the variation of lattice constant with zinc concentration deviates from Vegard's law [1]. The high temperature annealing changes the wet prepared ferrites into the ordered magnetic structure of the ceramic ferrites.     

Magnetization Process of the Spin-1/2 Two-Leg Ladder Compound (C5H12N)2 CuBr4: The Jordan-Wigner Approach

We have studied the magnetization process in the spin S = 1/2 antiferromagnetic two-leg ladder compound (C₅H₁₂N)₂ CuBr₄ by using the analytical fermionization technique. The magnetization and the susceptibility are calculated as functions of the temperature and the external magnetic field. The magnetization of the system shows various behaviors in different regions of the magnetic field. The field-dependence of the susceptibility is almost symmetric about the average of quantum critical fields in the low-temperature region leading to a complete agreement with the experimental results.     

明胶-铁氧化物纳米复合微粒的制备和性能

用微乳液法制备了明胶包裹的复合氧化铁纳米量级超细微粒。XRD,TEM,SEM和IR测试表明:微粒为明胶包裹球形超细微粒。微球的粒径为1.5 μm~3 μm,而微粒的粒径为20 nm。每个复合微球中约有35个~90个氧化铁粒子。该复合微粒的比饱和磁化强度σ_s=62Am2/kg,矫顽力Hc=187 Oe,剩磁r=10.18Am2/kg,具有硬磁体的性质。将其用于制备磁流变液,在低的磁场强度下有较大的MR效应,沉降稳定性优于用羰基铁粉制成的磁流变液。     

Synthesis and electrophoretic deposition of magnetic nickel ferrite nanoparticles

Powders with particle size ∼5–15 nm of nickel ferrite have been synthesized chemically from aqueous precursor solutions. From the structural and magnetic properties, it is determined that the synthetic material possesses high NiFe₂O₄ phase purity and controllable particle size. The optimum calcination temperature is found to be ∼500 °C, at which the NiFe₂O₄ particles exhibit a saturation magnetization of 2800 G, and a particle size of about 10 nm. The particles are then deposited onto silicon substrates by electrophoretic deposition (EPD) process. The Ni ferrite particles are suspended in a medium of isopropyl alcohol with magnesium nitrate and lanthanum nitrate salts as charging agents. The transportation of particles to the substrate surface is assisted by applied electric field and particles adhere to the substrate surface by a glycerol based surfactant. The magnetic response of the EPD film has been investigated by vibrating sample magnetometer (VSM) measurements.     

Magnetic properties of Ni0.5Ag0.5 thin films

Ni_0.5Ag_0.5 thin films were prepared by R.F. sputtering. The magnetic properties (saturation magnetization and susceptibility) was measured by means of a Faraday balance in the temperature range 170–715K. The films are made up of fine particles of pure nickel scattered in an amorphous matrix. Below 400K the films are paramagnetic and above they have a superparamagnetic behaviour. We have also shown that the large particle size distribution leads to exchange integral fluctuations.     

Monte Carlo Study of Magnetic Properties in Semiconducting MnTe

The magnetic properties of antiferromagnetic MnTe alloys have been studied by Monte Carlo simulations within Ising model framework. The considered Hamiltonian includes nearest-neighbor interactions, external magnetic field, and crystal field. Magnetizations and magnetic susceptibility versus temperature are computed for a fixed size. The blocking temperature is established, and the magnetic hysteresis cycle is deduced for different values of temperature. The remanent magnetization and the coercive field are obtained. In addition, the magnetization versus the first exchange interaction (J ₁) with a fixed value of the second exchange interaction (J ₂) and the third second interaction (J ₃) is estimated. The magnetization versus the crystal field is deduced.     

Magnetic interactions in ball-milled spinel ferrites

Spinel Fe₃O₄ nanoparticles have been produced through ball milling in methyl-alcohol (CH₃OH) with the aim of producing samples with similar average particle sizes (d) and different interparticle interactions. Three samples with the Fe₃O₄ to CH₃(OH) mass ratios R of 3, 10 and 50 wt% were milled for several hours until particle size reached a steady value (d) ～6-10 nm). A detailed study of static and dynamic magnetic properties has been undertaken by measuring magnetization, ac susceptibility and Mössbauer data. As expected for small particles, the Verwey transition was not observed, but instead superparamagnetic (SPM) behavior was found with transition to a blocked state at T _B ～10-20 K. For samples having 3 wt% of magnetic particles, dynamic ac susceptibility measurements show a thermally activated Arrhenius dependence of the blocking temperature with applied frequency. This behavior is found to change as interparticle interactions begin to rule the dynamics of the system, yielding a spin-glass-like state at low temperatures for R = 50 wt% sample.     

Susceptibility and magnetization studies of Gd3+ substituted Mg-Cd ferrites

Studies on lattice parameters, magnetization and ac susceptibility measurements for the ferrite system Cd _x Mg_1−x Gd _y Fe_2−y O₄ (withx = 0·2, 0·3, 0·4 andy = 0·1, 0·2, 0·3, 0·4) are presented. The ac susceptibility was measured from room temperature to 800K at a constant magnetic field of 7 oersted.X _ac vsT variations show that all the samples contain predominantly multidomain (MD) particles. Magnetization measurements of the system indicate that as the Cd²⁺ content increases magnetization increases while the addition of Gd³⁺ reduces the magnetization. The observations further indicate the existence of Y-K type of magnetic ordering in the system.