Effect of aggregates on the magnetization property of ferrofluids: A model of gaslike compression

The effect of field-induced aggregation of particles on the magnetization property of ferrofluids is investigated. From the viewpoint of energy, magnetizability of ferrofluids is more complicated than predicted by Langevin theory because the aggregation, i.e., the transition of ferrofluid microstructure, would consume the energy of the applied magnetic field. For calculating the effect of aggregates on the magnetization of ferrofluids, a model of gaslike compression (MGC) is proposed to simulate the evolution of the aggregate structure. In this model, the field-induced colloidal particles aggregating in ferrofluids is equivalent to the “gas of the particles” being compressed by the applied magnetic field. The entropy change of the ferrofluid microstructure is proportional to the particle volume fraction in field-induced aggregates ø_H. On the basis of the known behavior of ferrofluid magnetization and the aggregate structure determined from the present experiments, ø_H is obtained and found to depend on the aggregating characteristic parameter of ferrofluid particles γ in addition to the particle volume fraction in ferrofluids ø and the strength of applied magnetic field H. The effect of the nonmagnetic surface layer of ferrofluid particles is also studied. The theory of MGC conforms to our experimental results better than Langevin theory.     

水垢的预测与磁化处理技术

本文分析了我国北方水系水垢的形成原因和水垢的常规防治及清除方法存在的局限性，研究了磁化除垢的机理，介绍了磁化除垢设备的结构和应用。     

Characterization and Magnetic Properties of Cobalt Nano-Particles Prepared by Metal Vapor Synthesis Technique

The metal vapor synthesis technique was employed to prepare Co nanoparticles. The characteristics and properties of the particles were studied by transmission electron microscopy, X-ray diffraction, temperature-programmed desorption,chemisorption and magnetic measurements. The experimental results showed that the particle size of Co powders depended on the initial Co concentration in the toluene matrix, reaching average crystallite diameter of 1.5 nm for the highest concentration (6.4 at. pct) investigated. The particles with size of 10 nm exist, due to the agglomerates of microcrystallites. The Co particles were surrounded by a thin carbonaceous layer formed due to toluene decomposition on cocondate melt-down and subsequent warming to room temperature. The carbonaceous layer was composed primarily of C1 fragments. The Co powders demonstrated ferromagnetic behavior.     

Tunable multiferroic properties of Mn substituted BiFeO3 thin films

The current study explored the influence of Mn substitution on the electrical and magnetic properties of BiFeO₃ (BFO) thin films synthesized using low cost chemical solution deposition technique. X-ray diffraction analysis revealed that pure rhombohedral phase of BiFeO₃ was transformed to the tetragonal structure with P4mm symmetry on Mn substitution. A leakage current density of 5.7×10⁻⁴ A/cm² which is about two orders of magnitude lower than pure BFO was observed in 3% Mn doped BFO thin film at an external electric field >400 kV/cm. A well saturated (p-E) loops with saturation polarization (P_sat) and remanent polarization (2P_r) as high as 60.34 µC/cm² and 25.06 µC/cm² were observed in 10% Mn substituted BFO thin films. An escalation in dielectric tunability (n_r), figure of merit (K) and quality factor (Q) were observed in suitable Mn doped BFO thin films. The magnetic measurement revealed that Mn substituted BFO thin films showed a large saturation magnetization compared to pure BFO thin film. The highest saturation ~31 emu/cc was observed for 3% Mn substituted BFO thin films.     

水玻璃磁化改性的工艺参数研究

系统地研究了水玻璃模数、流速和磁场强度等诸因素对水玻璃砂粘结强度的影响，通过优化设计，确定了水玻璃磁化改性的最佳工艺参数。研究表明，磁化处理可提高水玻璃的粘结强度３０％～４０％，从而可相应减少型砂中水玻璃的加入量，改善水玻璃砂的溃散性。磁化处理可以在输送水玻璃的管道中进行。     

Magnetic properties of Al–Gd–Ni orthorhombic compounds

The magnetic properties of the Al₄GdNi, Al₂GdNi and AlGd₂Ni₂ compounds have been investigated using magnetic measurements in the temperature range 4–800 K and magnetic fields up to 9 T and X-ray photoelectron spectroscopy at room temperature. The compounds Al₄GdNi and AlGd₂Ni₂ order antiferromagnetically at T_N = 20 and 25 K, respectively, and Al₂GdNi orders ferromagnetically at T_C = 39 K. The results are discussed in terms of the Ruderman–Kittel–Kasuya–Yosida theory, the polarization of 5d electrons by the local exchange interaction 4f–5d and the spin fluctuations on Ni sites.     

Magnetic and transport properties of YbRhIn and YbPdIn

Electrical resistivity, magnetization and specific heat have been measured on a single crystal of YbRhIn and polycrystals of LuRhIn and YbPdIn. It is confirmed that YbPdIn is a metal with a divalent Yb ion. For YbRhIn, the electrical resistivity increases with logarithmic temperature dependence with decreasing temperature and saturates at a constant value below 20 K, while that of the nonmagnetic reference LuRhIn shows typical metallic behavior. The magnetic susceptibility of YbRhIn indicates that the Yb ion is in the trivalent state. The irreversibility of the magnetization curves which is observed in the high pulsed magnetic field below 1.5 K suggests an increase of relaxation time in the magnetic system. The specific heat increases rapidly below 4 K with decreasing temperature down to 0.9 K and moves toward higher temperatures on application of a magnetic field. These facts suggest that some magnetic transition to either ferromagnetic or spin-glass state occurs at low temperature.     

Theoretical consideration of nondestructive testing by use of vertical magnetization and magneto-optical sensor

This paper describes a new magnetization method for non-destructive testing with magneto-optical sensor (denoted as MO sensor) which have the following characteristic; high observation sensitivity, independence of the crack orientation, and precise imaging of a complex crack geometry such as multiple cracks. When a magnetic field is applied normally to the surface of a specimen which is significantly larger than its defects, approximately the same magnetic charge per unit area occurs on the surface of the specimen. If there is a crack in the specimen, magnetic charge per unit area has the same value at the bottom of the crack. The distribution of the vertical component of the magnetic flux density, B_z, is almost uniform over the no-crack area (denoted as B_{Z, BASE}), while the magnetic flux density is smaller in the surroundings of the crack (denoted as B_{Z, CRACK}) : If B_{Z, BASE} is a bit larger than the saturated magnetic flux density of the MO sensor (B_S), then small magnetic domains occur over the crack area and a large domain over the non-crack area because B_{Z, CRACK} is smaller than B_s.     

Enhanced magnetic and dielectric properties of Y doped bismuth ferrite nanofiber

Yttrium doped Bismuth ferrite (BFO) nanofiber was fabricated via a sol-gel-based electrospinning process with the fiber diameter in the range of 60–220 nm. The crystal structure, magnetic and dielectric properties were investigated at room temperature. The Rietveld refinement results indicate the phase transition from space group R3c to Pbnm by the Y doping. Dramatic increase of magnetization has been achieved in Y doped BFO nanofiber. Compared with BFO nanoparticle, the Bi_0.95Y_0.05FeO₃ nanofiber exhibits nearly eighteen-fold improved magnetization, which is the strongest in the reported Y doped BFO at the same doping level. The largely improved magnetization mainly originates from the serious suppression of spiral spin structure by the small crystal size of nanofiber structure. Moreover, the Bi_0.95Y_0.05FeO₃ nanofiber holds the lower dielectric loss and obvious dependence of the capacitance on bias voltage, indicating the improved ferroelectricity due to the decreased leakage current. The simultaneous enhancement of ferroelectricity and magnetization in Y doped BFO nanofiber suggests that nanofiber structure plays an important role in improving multiferroic performance.     

Magnetic and Magnetotransport Properties of Diluted Magnetic Semiconductor (Ga,Mn)Sb Crystals

We report the magnetic and magnetotransport properties of Ga_1−x Mn _x Sb crystals grown with different Mn doping concentrations (x=0.01, 0.02, 0.03 and 0.04) by the horizontal Bridgman technique. A systematic reduction in lattice parameter with increase in Mn concentration is observed through X-ray diffraction studies. The crystals show negative magnetoresistance and anomalous Hall effect below 10 K. Anomalous Hall coefficient is negative and decreases with increasing Mn concentration. Temperature dependence on magnetization measurement shows a magnetic ordering below 10 K which could arise from GaMnSb alloy formation. Also, ferromagnetism is observed till room temperature due to the presence of MnSb clusters. Existence of MnSb clusters is verified through scanning electron microscopy. The carrier concentration increases with Mn doping and this results in decrease of resistivity. The observed magnetic and transport properties indicate the presence of ferromagnetic phase below 10 K in the studied system.