Papers by Keyword: Saturation Magnetisation

Abstract: The preference site and magnetic property of doped Cr atom in L1₀ FePt alloy are investigated by the first-principles calculations. Due to the energy of Cr located in Fe and Pt sublattice are -0.15 and 0.48 eV, respectively, the Cr atom occupying Fe site is more energetic favorable than in Pt site in L1₀ FePt alloy. The calculated saturation magnetizations for Cr additive replacing Fe or Pt atom in L1₀ FePt are 959 or 989 emu/cm³, respectively. The results are lower than that of L1₀ FePt (1085emu/cm³). The additive of Cr in L1₀ FePt will reduce the saturation magnetization.

Abstract: Co²⁺-doped Fe₃O₄ magnetic nanoparticles were synthesized via the solvothermal method with reaction system of H₂O and glycol in a high pressure autoclave. The products are of the inverse spinel structure confirmed by X-ray Diffraction. Fourier Transform Infrared Spectroscopy, Transmission Electron Microscope, Particles Size Analyzer and AC Gradient Magnetometer are also used to characterize the particles. The obtained Co²⁺-doped Fe₃O₄ magnetic nanoparticles display well crystalline state. Those particles are globular of which the diameter is above 15 nm with homogeneous size distribution, smaller than 20 nm of the non-doped products. Co²⁺-doped Fe₃O₄ magnetic nanoparticles show superparamagnetic behavior, and the saturation magnetization is 76.84 emu/g, which is higher compared with 54.42 emu/g of the non-doped. In the crystals structure of Fe₃O₄ magnetic nanoparticles, ferric ions occupy the tetrahedral sites and one-half of octahedral sites, and the ferrous ions occupy the remaining half of the octahedral sites. The magnetic moments of cations on tetrahedral and octahedral sites are anti-parallel. Therefore, the net moment is provided by the divalent ions. In the preparation process, bivalent cobalt ions replace the partial sites of the ferrous ions and the ferric ions, and enhance the net magnetic moment. Above all, the doping of Co²⁺ could improve properties of the Fe₃O₄ magnetic nanoparticles, i.e., enhancing the saturation intensity, decreasing the particle size and making the size distribution homogeneous.

Abstract: A nanocrystalline surface layer is produced in Co plate by surface mechanical attrition treatment (SMAT). The characterization of microstructure and composition indicates that elements of Fe, Cr diffuse from hardened steel balls into the surface layer during SMAT. The diffusion phenomenon results in the composition deviation in the surface layer, leading to higher value of saturation magnetization (M_s) for nanocrystalline Co surface layer in comparison with its coarse-grained counterpart.

Abstract: Nanocrystalline nickel ferrite has been successfully synthesized through carbon-adsorb auto combustion method from Ni and Fe nitrate salts. The powders were characterized by X-raydiffraction(XRD) techniques,scanning electron microscopy(SEM),transmission electron microscopy(TEM) and vibrating sample magnetometry(VSM). XRD indicated that the products were spinel NiFe₂O₄. SEM and TEM indicated that the particles were spherical with particle size in the range 10-80nm. VSM showed that the sample exhibited typical ferromagnetic behavior at room temperature,while the coercivity of the sample was 150.45Oe and the residual magnetization of the sample was 5.1emu/g.The saturation magnetization of the sample(25.3emu/g)was lower than that for the reported bulk particles(55emu/g), and it has the ultrafine nature.

Abstract: SUS316L austenitic stainless steel was subjected to severe plastic deformation (SPD) by the method of high pressure torsion (HPT). From a fully austenitic matrix (γ), HPT resulted in phase transformation from g®a¢. The largest volume fraction of 70% a¢ was obtained at 0.2 revolutions per minute (rpm) while was limited to 3% at 5rpm. Pre-straining of g by HPT at 5rpm decreases the volume fraction of a¢ obtained by HPT at 0.2rpm. By HPT at 5rpm, a¢®g reverse transformation was observed for a¢ produced by HPT at 0.2rpm.

Abstract: Magnetic properties of iron-containing coatings obtained on aluminum by plasma electrolytic oxidation were analyzed in this paper. Theoretical curves of demagnetization of these objects are obtained. It is shown that the magnetic states of the analyzed samples can be caused by the presence of several phases with very different magnetic properties.

Abstract: SUS 304 austenitic stainless steel (ASS) was deformed by high pressure torsion (HPT) to obtain 100% volume fraction of martensite (α') from a fully austenitic (γ) matrix. Deformation caused an increase in hardness (Hv) from 1.6 GPa in the as annealed state to 6.4 GPa　after HPT. Deformed samples were then annealed in the range 200 – 600oC and peak hardness of 7.8 GPa was observed after annealing at 400oC for 1 hour. Differential scanning calorimetry (DSC) and electrical resistivity tests showed that the deformed alloy undergoes a two stage phase transformation on heating from room temperature up to 700oC. The first stage of transformation was associated with hardening behavior while the second one which is reverse α' → γ transformation resulted in a reduction in hardness. Annealing at 400oC after deformation was found to increase the magnetization saturation (Msat) values.

Abstract: This paper presents measured magnetic and shape memory properties of Fe-Mn-Cr-Si-Sm-B ferromagnetic shape memory ribbons depending on tensile stress and temperature. The samples were produced with the melt spinning method in air and the magnetic properties were measured with an open solenoid type measurement system under controlling their temperature and tensile load. The alloys are multi-functional materials, which have both the ferromagnetic property and shape memory property. The measured results show applicability of the produced ribbon in applications for magnetic sensors and actuators.

Abstract: 1J79 alloy was prepared by vacuum electric arc smelting．The crystal growth and the content of impurity was observed by electron probe microanalyzer，and magnetic properties were measured by vibrating sample magnetometer(VSM)．Experimental results show that inclusions in the alloy are fewer and fewer, composition becomes more uniform with the increases of the Mo content, and grain size also becomes larger and larger with the increases of Mo content, to reduce coercivity. The small amount of Mo addition is useful to improve the saturation magnetization and reduce coercivity．

Abstract: Adopting chemical coprecipitation and mechanical dispersion to prepare oil based magnetic fluid is a good way to increase the stability of magnetic fluid. This paper uses orthogonal design to analyze the influences from different factors, and The size of nano-particles and saturation magnetization were characterized by TEM and WSM vibration magnetometer. The results show that the NaOH solution adding speed of 0.4 ml/s and reaction temperature of 50 ~55 , sodium oleate solution adding speed of 0.3ml/s and heating temperature of 65 , heat-maintaining time of 20min are proper reaction conditions.