Papers by Keyword: Coercivity

Abstract: Electroless plating was used to coat Fe layers on the hard magnetic Nd-Fe-B powders to fabricate Nd-Fe-B/α-Fe heterostructured magnetic powders. The heat treatment was performed to study the property evolution of the heterostructured magnetic powders. The results show that Fe coating was oxidized to Fe₂O₃ while drying; through the hydrogen reduction annealing, Fe₂O₃ was reduced to α-Fe. The coercivity of the heterostructured magnetic powders increased from 111.3 kA/m (1.4 kOe) to 524.7 kA/m (6.6 kOe) after annealing at 650°C. However, the demagnetization curve of powders presents a kink due to un-ideal coupling between hard and soft magnetic phases because of the aggregation of α-Fe. The magnetization processes of the heterostructured powders transferred from the dominant nucleation mechanism to domain wall pinning mechanism after the heat treatment.

Abstract: Monodispersed magnetic SmCo nanoparticles have been prepared by polyol synthesis using non-toxic inorganic precursors (nitrates). The effect of the additives of NaOH, HNO₃, CH₃COOH and poly vinyl pyrrolidone (PVP) on the formation of SmCo nanoparticles is studied in this paper. The results indicate that base solution can boost the reduction of Co while acid solution is helpful for the formation of SmCo due to decreasing the reduction velocity of Co. CH₃COOH is appropriate additive for the synthesis of SmCo nanoparticles, but more addition of CH₃COOH will result in the emergence of CoC₂ phase and decrease the coercivity of the resultants. The additive of PVP not only is a dispersing agent, but can prevent them from oxidating during preparation process. The SmCo nanoparticles with a size of 5-8 nm have the ferromagnetic properties of high coercivity (>1000 Oe).

Abstract: Sm₂Co₁₇:Cu,Cr films growing on Cr buffer layer and Cu seed layer were prepared by pulsed laser deposition(PLD) method based on Si(100) substrate. The results showed that Cu and Cr co-doped in SmCo films made the refinement of crystal grain and the increase of coercivity of SmCo. Beside, the experiments found that the incorporation of Cu and Cr in SmCo films resulted in a positive effect of the exchange bias for SmCo-CuCr system. We suggested that the mechanism of the exchange bias origins from the interaction of ferromagnetic-antiferromagnetic state (FM-AFM, SmCo-CuCr). Meanwhile, the magnetic measurment of added magnetic field and zero-field-cooled (FC-ZFC) at temperature range of 10K~300K has further confirmed the critical value of FM-AFM tansform is about 80K, which is suggested that it was attributed to the coupling competition of FM phase and AFM phase.

Abstract: Nanoparticles of MgFe₂O₄ with average crystallite size of ~ 8 nm have been synthesized employing non-aqueous combustion method. Structural properties of the nanoparticles are analyzed with the help of X-Ray Diffractometry (XRD), Scanning Electron Microscopy (SEM), Energy dispersive X-Ray analysis (EDX), Fourier Transform Infra-Red spectroscopy (FT-IR). X-Ray Diffraction pattern and FT-IR spectra reveal the formation of spinel structure of MgFe₂O₄ nanoparticles. The SEM micrographs of the sample show the formation of clusters of spherical particles with pores revealing the history of synthesis as combustion process. The constituent elements and chemical composition are analyzed using EDX spectrum. Magnetic study done using Vibrating Sample Magnetometer (VSM) reveals that the prepared nanoparticles remain unsaturated within the field of 15 kOe and have a very low coercivity of 20 Oe.

Abstract: LaFeO₃/Fe₂O₃ and Mn₂O₃/Fe₂O₃ magnetic nanocomposites have been prepared by a modified polyacrylamide gel route. The XRD result indicates the formation of LaFeO₃/Fe₂O₃ and Mn₂O₃/Fe₂O₃ nanocomposites. Scanning electron microscope (SEM) observation shows that the LaFeO₃/Fe₂O₃ particles appear to be regularly spherical in shape and highly uniform in size with a diameter of ~ 80 nm, while the Mn₂O₃/Fe₂O₃ sample exhibits a relatively broad particle size distribution with an average particle size centered around 20-60 nm. Result of vibrating sample magnetometer (VSM) of LaFeO₃/Fe₂O₃ magnetic nanocomposites revealed that coercivity values decreased with the increase sintering temperature. However, the coercivity values of Mn₂O₃/Fe₂O₃ magnetic nanocomposites appear to an anomaly phenomenon.

Abstract: We report on experimental results of the temperature dependence of inductive (total) magnetic moment and remanent magnetic moment at saturation field for electrodeposited nanocrystalline Ni films with thicknesses ranging from 350 nm to 20 μm. We have found that the amplitude of roughness and crystallite size significantly affected the remanent saturation magnetic moment and coercivity.

Abstract: The magnetic and electrical properties of Co/Ge bilayer films are experimentally studied. It is established that at the Co/Ge interface an intermediate magnetic layer forms. This layer affects the magnetic behavior and magnetoresistive effect in the investigated structures.

Abstract: The dependence of free layer coercivity on the angle between easy axis and applied magnetic field was studied on [Ta, (Ni₈₀Fe₂₀)₆₀Cr₄₀]/ Ni₈₀Fe₂₀/Co₉₀Fe₁₀/Cu/Co₉₀Fe₁₀/Mn₇₅Ir₂₅/Ta spin valves with various interlayer coupling. Sharp decrease on the angle was observed for ferromagnetically coupled spin valves. The coercivity was reduced down to tenth of Oersted without any decrease of GMR-effect by forming nearly parallel anisotropy configuration. The angles at which the transition from hysteretic to anhysteretic magnetic reversal takes place are detected by analyses of the angle dependence of coercivity. Interpretation of experimental data is based on Stoner-Wohlfarth coherent rotation approach.

Abstract: The present work investigates texture evolution stages in vacuum-degassed non-oriented electrical steels. The main idea behind the improvement of soft magnetic properties relies on deformation induced grain growth phenomena and heat transport phenomena promoting the preferable formation of columnar grains with so called cube crystallographic orientation {100}<0vw>. In order to achieve the desired orientation with appropriate microstructure state from magnetic properties point of view, we have used an adjusted temper rolling process at elevated temperature and subsequent dynamical annealing in laboratory conditions.

Abstract: Fe/SiO₂/shellac composites based on iron powder consisting of irregularly and/or spherical shaped particles coated with SiO₂ layer or with admixed SiO₂ powder were prepared either by mixing the Fe-SiO₂ powder with shellac or by vacuum/pressure impregnation (VPI) of sintered Fe-SiO₂ compacts with shellac dissolved in ethanol. The effect of iron particle shape, density of compacts and method of shellac application on electrical resistivity and magnetic coercivity was evaluated and correlated with microstructure and features of insulating layer. For VPI composites based on spherical particles a uniformly thick insulating layer was created. This resulted in the electrical resistivity and coercivity of 780-1120 μΩ.m and 177-290 A/m. For composites based on irregularly shaped particles the shellac admixing is more preferable.