Reduction Of Coercive Force Research Articles

Composition of the Frenkel\u2013Kontorova and Ising models for investigation the magnetic properties of a ferromagnetic monolayer on a stretching substrate

In the article, computer simulation on the behavior of a ferromagnetic thin film on a non-magnetic substrate by computer simulation is performed. The substrate is described by the two-dimensional Frenkel–Kontorova potential. The Ising model is used to describe the magnetic properties of a two-dimensional ferromagnetic film. The Wolf cluster algorithm is used to model the magnetic behavior of the film. A square lattice is considered for an unperturbed ferromagnetic film. Computer simulations show that mismatch of film and substrate periods results in film splitting into regions with different atomic structures. Magnetic properties for the obtained structure have been investigated. The hysteresis loop is calculated using the Metropolis algorithm. Deformations of the substrate lead to a decrease in the phase transition temperature. The Curie temperature decreases both when the substrate is compressed and when stretched. The change in phase transition temperature depends on the decreasing rate of exchange interaction with distance and the amplitude of interaction with the substrate. When the substrate is compressed, an increase in the amplitude of the interaction between the film and the substrate results in an increase in the phase transition temperature. The opposite effect occurs when the substrate is stretched. The hysteresis loop changes its shape and parameters when the substrate is deformed. Compression and stretching of the substrate results in a decrease in coercive force. The reduction in coercive force when compressing the substrate is greater than when stretching. The magnetization of the film is reduced by deformations at a fixed temperature.

Magnetic behavior in commercial iron-silicon alloys controlled by the dislocation dynamics at temperatures below 420 K

A decrease of the temperature dependent coercive forces up to around 370 K is discovered in iron silicon alloys, both in quenched samples and in samples which were previously thermally treated to achieve the highest magnetic quality. Alloys of composition Fe-6 wt.% Si and Fe-3 wt.% Si are studied. This reduction in the coercive force is controlled by an increase in the mobility of the domain walls due to the increase in the dislocation’s mobility enhanced by the movement of vacancies. It is worthwhile to mention that this reduction in coercive force is only present at these slightly elevated temperatures which are markedly smaller than the usual annealing temperatures for heat treatment of iron silicon alloys while it disappears again at room temperature. Neutron thermodiffraction, magnetic hysteresis loops tracer and mechanical spectroscopy are used as experimental techniques.

Cu2+ and Al3+ co-substituted cobalt ferrite: structural analysis, morphology and magnetic properties

Cu–Al substituted Co ferrite nanopowders, Co1−x Cu x Fe2−x Al x O4 (0.0 ≤ x ≤ 0.8) were synthesized by the co-precipitation method. The effect of Cu–Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu–Al substitution and its impact on particle size, magnetic properties such as M s and H c . Cu–Al substitution occurs and produce a secondary phase, α-Fe 2 O 3. The crystallite size of the powder calcined at 800 ∘C was in the range of 19–26 nm. The lattice parameter decreases with increasing Cu–Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 (v 1) and 400 cm −1 (v 2). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu–Al contents. The saturation magnetization decreases with the increase in Cu–Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction.

Structural, electrical, magnetic and dielectric properties of rare-earth substituted cobalt ferrites nanoparticles synthesized by the co-precipitation method

Pure nanoparticles of the rare-earth substituted cobalt ferrites CoRExFe2−xO4 (where RE=Nd, Sm and Gd and x=0.1 and 0.2) were prepared by the chemical co-precipitation method. X-ray diffraction, Transmission electron microscopy (TEM), d.c. electrical conductivity, Magnetic hysteresis and Thermal analysis are utilized in order to study the effect of variation in the rare-earth substitution and its impact on particle size, magnetic properties like MS, HC and Curie temperature. The phase identification of the materials by X-ray diffraction reveals the single-phase nature of the materials. The lattice parameter increased with rare-earth content for x≤0.2. The Transmission electron micrographs of Nd-, Sm- and Gd-substituted CoFe2O4 exhibit the particle size 36.1 to 67.8nm ranges. The data of temperature variation of the direct current electrical conductivity showed definite breaks, which corresponds to ferrimagnetic to paramagnetic transitions. The thermoelectric power for all compound are positive over the whole range of temperature. The dielectric constant decreases with frequency and rare-earth content for the prepared samples. The magnetic properties of rare-earth substituted cobalt ferrites showed a definite hysteresis loop at room temperature. The reduction of coercive force, saturation magnetization, ratio MR/MS and magnetic moments may be due to dilution of the magnetic interaction.

Influence of laser processing and magnetically active inorganic coatings on the dynamic magnetic properties of soft-magnetic materials

We have studied the influence of magnetically active inorganic coatings and local laser processing on grain-oriented steels (Fe-3% Si) and amorphous alloys (Fe78Ni1Si9B12 (2NSR), Fe81Si7B12, and Fe81Si4B13C2). The potentialities of different types of laser processing have been assessed. Local laser processing and coating parameters have been shown to have a significant effect on the domain structure and electromagnetic properties of the materials. A reduction in coercive force and magnetic loss by 20–28% has been demonstrated.

Photo-carrier-induced magnetism in (In,Mn)As/GaSb magnetic alloy semiconductor heterostructures

We present wavelength dependence of photo-carrier-induced magnetization for (In,Mn)As/GaSb heterostructures, and discuss the problem involved in hole transfer from GaSb to (In,Mn)As across the (In,Mn)As/GaSb heterointerface. The reduction in coercive force by the light illumination has also been shown as a new effect associated with carrier-induced magnetism.

926 ハードフェライト粉の圧縮成形過程における保磁力の低下に及ぼす圧力の作用状態の影響

926 ハードフェライト粉の圧縮成形過程における保磁力の低下に及ぼす圧力の作用状態の影響

Magnetic properties of FeCoV film sandwiched by thin soft-magnetic films

Soft magnetization of FeCoV thin films has been examined experimentally. The coercive force of FeCoV films decreases by more than 90% with little reduction in saturation magnetization or changes in magnetization behavior when films are sandwiched between two thin FeNiMo soft-magnetic layers making up about 2% of the total volume. It can be assumed that a magnetic wall, parallel to the film surface and formed at the interface between the soft-magnetic layer and the FeCoV layer, will readily propagate into the FeCoV layer. The thickness of the soft-magnetic layer necessary for the magnetic wall formation is thought to be about 50/spl sim/100 /spl Aring/. The reduction in coercive force seems to be related to the anisotropy of the magnetic properties of the thin soft-magnetic layer. In the case of Fe films, however, a reduction in coercive force due to the thin soft-magnetic layer never occurs. Whether the thin soft-magnetic layer has effects on the crystal structure of FeCoV or Fe layers, will be examined experimentally in the future.

Effect of light illumination on the process of magnetization reversal in carrier-induced ferromagnetic semiconductors

We have found the reduction in coercive force by the light illumination for carrier-induced ferromagnetic semiconductor heterostructure p-(In,Mn)As/GaSb grown by molecular beam epitaxy. This effect disappears when the photogenerated holes recombine with trapped electrons. This strongly suggests that the observed phenomenon is attributed to the carrier-induced magnetism.

Control of magnetization reversal process by light illumination in ferromagnetic semiconductor heterostructure p-(In, Mn)As/GaSb

The reduction in coercive force by light illumination has been found in ferromagnetic semiconductor heterostructure p-(In, Mn)As/GaSb prepared by molecular-beam epitaxy. Enhanced ferromagnetic coupling between Mn ions, arising from excess photogenerated holes, reduces the domain wall energy and changes the magnetization hysteresis characteristics. The value of coercive force returns to the original value when excess holes recombine with trapped electrons.

The effect of sputter-deposition conditions on the coercive force in amorphous rare-earth-transition-metal thin films

The origins of the coercive force in amorphous rare-earth-transition metal films have been investigated. The results are discussed in terms of how the growth conditions of the sputter-deposited films determine the pinning features that cause the coercive force. A model has been developed for the variation of coercive force with film thickness that enables a local pinning force per unit area to be deduced. This suggests that it should be possible to increase the coercive force by breaking up the microstructure with a multilayered structure. An increase in coercive force obtained by making such structures with tungsten is described. A reduction in coercive force obtained when the films are deposited in the presence of a perpendicular magnetic field is also reported and interpreted in terms of a growth annealing model. >

Effects of nitrogen, oxygen and air on the magnetic properties of sputtered CoCrTa thin film recording discs

The effects of partial pressures of oxygen, nitrogen and air on sputtered CoCrTa ternary alloys have been studied relative to their microstructure and magnetic properties. The results show that oxygen affects the crystallinity and orientation of Co ternary alloys more severely than nitrogen or air. The effect of air was intermediate between that of O/sub 2/ and N/sub 2/. Introduction of oxygen results in a very large reduction in coercive force of the films. The coercivity reduction due to nitrogen is moderate, and the effect of air is intermediate between the effects of O/sub 2/ and N/sub 2/. However, no significant change in saturation magnetization values are observed due to the introduction of impurity gases. >

結晶化Ｎｄ‐Ｆｅ‐Ｂ薄帯の磁気特性に及ぼす結晶化条件の影響

Effects of crystallization conditions on magnetic properties have been investigated in amorphous Nd-Fe-B ribbons. Amorphous Nd15Fe75B10 ribbons were obtained by the single roller quenching technique. These ribbons, which have improved ductility and tensile strength, are soft magnetically in the as-prepared state and can be hardened by crystallization. It is found that short time annealing at high temperature is desirable for crystallization to obtain good hard magnetic properties. X-ray diffraction analyses and SEM observations have revealed that flash crystallization results in precipitation of sub-micron Nd2Fe14B micro-crystals whose sizes are nearly that of a single domain particle, and in extremely high coercive force. Excessive annealing at high temperature causes growth of crystallites and reduction of coercive force. The ribbons crystallized in the best condition are magnetically isotropic and have Br of 7kG and (BH)max of 10.2 MGOe when magnetized by a pulse field of about 30 kOe.

Effect of ion bombardment during deposition on magnetic film properties

This paper reports on the effect of ion bombardment on the magnetic properties of sputtered cobalt/nickel films. Zero biased films exhibit coercivities in the range of 300 to 1400 oersted (Oe), and hysteresis squareness Mr/Ms values of 0.63 to 0.83, depending on thickness. Similar bias sputtered or ion bombarded films exhibit lower coercive force values. However, films sputtered at a negative 100 V bias contain less oxygen and exhibit a Hcp crystal orientation of (101̄1) as compared to zero bias films which exhibit a (101̄0) orientation. This may account for the reduction in coercive force.

Microstructure and Magnetic Properties of Lead Ferrite

Unoriented lead ferrite specimens were prepared by calcining and sintering techniques. Specimens having an initial composition of Pb0.5Fe2O3 had the best permanent magnet properties (for nondoped material). The effects of small amounts of added oxides on the microstructure and magnetic properties were also determined. Silica and boria were most effective in raising the (BaHa)max to over 1.4 × 106 G.Oe as compared to 0.9 to 1.1 × 105 G.Oe for commercial un oriented barium ferrite magnets. Optical and electron microscopy revealed that silica and boria form low melting phases as the specimens are sintered, which, acting as fluxes (probably by a solution‐precipitation mechanism), enhance the densification of the magnets, thereby raising the Br, and (BaHa)max, values. On cooling, these nonmagnetic low‐melting phases are retained at the ferrite grain boundaries where they inhibit domain wall motion which would otherwise lead to a reduction in coercive force. Although these magnets are termed “un oriented” to distinguish them from “oriented” ferrites which are purposely aligned before sintering, a slight orientation is imparted to the polycrystalline compact during the pressing operation before sintering. The silica and boria additions increase the degree of orientation by accelerating the rate of densification. The increase in orientation accounts for part of the increase in Br, and (Ba, Ha)max.

Theoretical Coercive Field for an Interacting Anisotropic Dipole Pair of Arbitrary Bond Angle

The coercive force for a pair of identical interacting uniaxially anisotropic dipoles of arbitrary bond angle is calculated for the case of the applied field coincident with the common anisotropy axis. The technique used is to examine the shape of the total energy surface about the equilibrium state as the applied field is lowered from an arbitrarily large initial value and subsequently reversed. At the nucleating field, the energy surface curvature disappears in some eigendirection which can be related to the initial mode of switching. An examination of the stability of available states to which the system may switch shows that for this simple model the nucleating field is identical to the coercive field. The results, which coincide with a planar solution, are expressed as coercive field versus pair bond angle for various pair separations. They differ significantly from the usual ``local field'' approach in which the magnetization is presumed to remain parallel to the applied field until nucleation. This exact collective treatment leads to a nonlinear reduction of coercive force with packing fraction for an ensemble of independent randomly oriented pairs, whereas the ``local field'' approach yields a coercivity independent of packing.

Reduction in Coercive Force Caused by a Certain Type of Imperfection

As a first approach to the study of the dependence of the coercive force on imperfections in materials which have high magnetocrystalline anisotropy, the following one-dimensional model is treated. A material which is infinite in all directions has an infinite slab of finite width in which the anisotropy is 0. The coercive force is calculated as a function of the slab width. It is found that for relatively small widths there is a considerable reduction in the coercive force with respect to perfect material, but reduction saturates rapidly so that it is never by more than a factor of 4.