Papers by Keyword: Saturation Magnetization

Abstract: Crystal structure and magnetic properties of Heusler-alloy Co₂MnGa were examined systematically using non-stoichiometric compositions of Co and Mn element from the Czochralski as-grown single crystal samples. The crystalline structure of each sample was characterized by means of X-ray powder diffraction technique. Each sample was treated with and without heat treatment at 923 K for 10 hours. The effects of Co and Mn excess were observed in the lattice constants for both treatments. The L2₁-type crystal structure was observed only for the heat-treated samples. The changes in lattice constants are attributed to the substitution of atomic sites. The excess of Co tends to decrease the crystal volume, in opposite to the excess of Mn. In order to investigate the Slater-Pauling rule in the non-stoichiometric samples, the saturation magnetic moments were measured from the field-dependent magnetization measurement for the as-grown samples at 2 K. The deviation from the Slater-Pauling rule was found in the lower concentration of valence electron which associated to the lower total fraction of both Co and Mn. This indicates that the magnetic interactions of these materials cannot only be contributed to the number of valence electron.

Abstract: Superparamagnetic iron oxide nanoparticles (SPION) were synthesized by one pot coprecipitation method at room temperature in the presence of Polyvinylpyrrolidone (PVP). X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Vibrating Sample Magnetometer (VSM) were used to analysis the physicochemical properties of PVP-SPION. The XRD patterns confirmed that the structure of as-synthesized sample is magnetite with cubic structure system. In TEM results, the image of PVP-SPION displayed that the size of particles was 14.05 nm with narrower size distribution and also the PVP played important role to minimize the agglomeration of SPION. Finally, the high saturation magnetization value of PVP-SPION (53.0 emu/g) indicate the as-synthesized sample has a great potential as a contrast agent for MRI.

Abstract: This paper presents the results of magnetic and microstructural study of cobalt-substituted NiZn ferrite powders, Ni_0.5Zn_0.3Co_0.2Fe₂O₄, synthesized with the solid-state reaction method. The lattice parameter decreased with Co substitution, as the ionic radius of cobalt is less than that of zinc. Raman spectroscopy showed clear peaks of the A_1g, E_g, and F_2g modes, revealing cubic spinel structure and good crystallinity of the samples. The saturation magnetization reduced in the substituted sample to 50.28 emu/g at room temperature. In comparison to the bulk ferrite, the powder sample showed pronounced coercivity even at room temperature. The temperature dependence of the magnetization had superparamagnetic curvature, which yielded the effective anisotropy constant equal to 8.832 kJ/m³.

Abstract: We have applied mechanical alloying technique to produce magnetic nanocomposite material using a mixture of Fe₂O₃ and Ca powders at room temperature. An optimal ball milling and heat treatment conditions to obtain magnetic α-Fe/CaO composite with fine microstructure were investigated by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer measurements. We have revealed that the magnetic α-Fe /CaO nanocomposite powders can be produced by solid state reduction during ball milling. It is found that α-Fe/CaO nanocomposite powders in which CaO is dispersed in α-Fe matrix with a grain size of 45 nm are obtained by mechanical alloying of Fe₂O₃ with Ca for 5 hours. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 65 emu/g after 7 hours of MA. The average grain size of a-Fe in 5 hours MA powders estimated by diffraction line-width are gradually decreased with increasing milling time, and tend to reach at 45 nm. The magnetic hardening due to the reduction of the α-Fe grain size by MA is also observed.

Abstract: Iron-based amorphous alloys have attracted technological and scientific interests due to their excellent soft magnetic properties. In the present study, Ni_0.5Zn_0.5Fe₂O₄/Fe₇₆Si₉B₁₀P₅ soft magnetic composites cylinder of 15 mm diameter and 3 mm thickness was prepared by spark plasma sintering at the temperature of 780 K. The amorphous Fe-based soft magnetic composites Ni_0.5Zn_0.5Fe₂O₄/Fe₇₆Si₉B₁₀P₅ exhibited good magnetic properties after annealing treatment at temperature ranging from 643 K to 743 K. The beneficial effects of treatment under different temperatures were discussed in terms of the improved magnetic performance of Ni_0.5Zn_0.5Fe₂O₄/Fe₇₆Si₉B₁₀P₅ soft magnetic composites.

Abstract: In the present investigation, FeCo/Cu core shell nanoparticles were prepared by coating a Cu layer over FeCo alloy nanoparticles through displacement reaction. X-ray diffraction studies confirmed the presence of FeCo and Cu phases in the sample. The grain size and lattice strains of the core shell nanostructures were evaluated from the x-ray profiles by using single line profile analysis technique. The effect of annealing temperature on the magnetic properties of the core shell nanoparticles was studied by using a vibrating sample magnetometer. The results showed that the magnetic properties improve significantly after annealing the compacts of core shell nanoparticles under a magnetic field. Enhancement in magnetization was observed in the compacts with the increase in annealing temperature. Highest saturation magnetization value of 56 emu/g was recorded in the sample which was annealed at 600°C. It has been also found that the blocking temperature of the core shell nanoparticles increases with the increase in annealing temperature.

Abstract: In this paper the strategy of the extraction of an advanced simulation model of interior permanent magnet synchronous machine is suggested in order to be employed by Model Predictive Control schemes. The conventional dq-axis mathematical model is modified in order to include data derived from finite element analysis (FEA). Indirect interaction between FEA and circuit simulation enhances model fidelity embodying the influence of saturation and cross-coupling effects. The proposed method of developing a detailed simulation model opens new prospects on the control of electrical machines.

Abstract: Decrease of a switching field, H_sw, of the magnetic media with high magnetocrystalline anisotropy constant, K_u, can be handled by tilted-easy axis. Not only tilting easy direction of crystal but also optimum magnetic properties can improve writability. The effects of K_u and saturation magnetization, M_s, of L1₀-CoPt material of BPM with 45° tilted-easy axis are investigated in this article. The object oriented micromagnetic framework package based on Landau - Lifshitz - Gilbert equation has been used to analyze the magnetic properties of media in this paper. The results indicate that the H_sw decreases with decreasing K_u and increasing M_s. To achieve the H_sw lower than the maximum write head field, the K_u and M_s values should not be over 1.30 MJ/m³ and should exceed 0.30 MA/m, respectively.

Abstract: M-type barium ferrite (BaFe_l2O₁₉) receives much attention due to the remarkable properties of the bulk materials: large magnetic anisotropy, sufficient saturation magnetization, non-toxic, excellent chemical stability and good corrosion resistivity. Using stoichiometric amounts of iron nitrate, barium nitrate and sodium hydroxide as the starting materials, we have prepared BaFe_l2O₁₉ by hydrothermal synthesis method. The results show that when the n (Fe³⁺)/n (Ba²⁺) ratio of 6 and n (OH⁻)/n (NO₃⁻) ratio of 2, the morphology of BaFe₁₂O₁₉ is hexagonal platelets which approximately 800 nm in length and 50 nm in thickness. The coercivity of BaFe₁₂O₁₉ is 1286 Oe and the saturation magnetization is 23.7 emu/g. The BaFe₁₂O₁₉/phenolic resin composite has been prepared and the permeability of the BaFe_l2O₁₉/phenolic resin composite was measured.

Abstract: Hysteresis loops were plotted and dependence of coercive field, residual saturation magnetization and saturation magnetization on size of the Co-Au core-shell nanoparticles were calculated within the developed model. It was shown that decrease in the size of nanoparticles leads to decrease of the abovementioned characteristics. Calculated values of the hysteresis characteristics ​​are in good agreement with the experimental data.