Increase In Coercive Force Research Articles

Effect of crystalline properties on coercive force in iron acicular fine particles

Crystallographic properties and their size dependence in acicular fine particles of iron prepared by reduction fromα-FeOOH were investigated by transmission electron microscopy and compared with magnetic properties. Although both larger particles with an average needle length of 0.5μm and smaller ones of 0.2μm length have single domain configuration, the former are crystal lographicaIly polycrystalline while the latter are single crystal with a [100] axial orientation, an easy magnetization direction of iron. The coercive force, principally yielded by external shape anisotropy, is higher in smaller particles in spite of their inferior axial ratio. The intrinsic magnetocrystalline anisotropy is inferred to be the most responsible to give rise to this further increase of coercive force. The experimentally obtained values of magnetic properties are also compared with the theoretical estimation, which results semi-quantitatively in good accordance.

Correlation between positron lifetime results and magnetic behaviour upon relaxation and crystallization of an iron-based amorphous alloy

Positron lifetime, magnetization work and coercive force have been measured in an as-quenched, relaxed and crystallized Fe 81.5B 14.5Si 4 alloys glass. The magnetic softening and the simultaneous decrease of the positron lifetime is discussed in terms of a relaxation of amorphous structure. The positron lifetime is found to increase slightly upon crystallization, supposedly due to trapping at defects at the boundary of small crystallites formed in the beginning of crystallization. The onset of crystallization is accompanied by a rapid increase of coercive force and a less drastic change in magnetization work. The dependence of the positron lifetime on measuring temperature is discussed in terms of the microstructure.

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. >

Magnetic properties of new manganese ferrites submicron particles

New manganese defect metastable ferrites with spinal structure were prepared by oxidation at a temperature lower than 500°C of submicron manganese substituted magnetites, Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-x</inf> MN <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0 \leq x &lt; 1</tex> ). X-ray diffraction measurements and thermal analysis studies have been carried out on these systems. Low-temperature magnetic measurements have also been carried out. With these studies, it has been possible to depict the cation distribution in substituted magnetites and oxidized compounds, and to understand the complex process of oxidation. In defect spinels, vacancies are formed not only from oxidation of Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions, but also of Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. Manganese-rich compound with x = 0.97 having high content of Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> and Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> ions show an important increase in coercive force, which exceeds 700 Oe at 4.2 K.

Magnetic properties and microstructures of Fe-Cr-Co-base cold-rolled magnets

Sheet magnets of Fe-Cr-Co-base alloys can be inexpensively produced through a process consisting of spinodal-decomposition aging, intermediate cold rolling, and final aging. In the present study magnetic properties have been greatly improved by adding Si, Ti, and Cu to the base alloys. The addition of Si raises the coercive force by increasing the amount of paramagnetic (or weak ferromagnetic) Cr-rich matrix phase. The addition of Ti increases remanence and maximum energy product by suppressing the precipitation of nonmagnetic σ phase during the final aging. The addition of Cu leads to a slight increase in coercive force. The best magnetic properties obtained in this study are iHc=790 Oe, Br=10.6 kG, and (BH)max=4.5 MGOe with a Fe-33.3 wt. % Cr-11.9 wt. % Co-1.05 wt. % Si-0.22 wt. % Ti-2.07 wt. % Cu alloy.

パーマロイ薄膜の磁気特性に及ぼす基板の材質と表面粗度の影響

Permalloy films of about 350A thickness evaporated on SiO2 and Ti films were annealed in a vacuum of 5 × 10-6 Torr at 250°C. The selective oxidation of Fe was confirmed by both IMA and EPMA measurements for the films prepared on the SiO2 film, but not on the Ti film. The oxidation causes the increase of coercive force. Further, Permalloy films were evaporated or sputtered on the Ti films which were prepared on glass substrates having a different surface roughness. The coercive force increased markedly with the increase of surface roughness for the evaporated films but not for the sputtered films.

Magnetic Properties of Insoluble Binary System Thin Film

Annealing insoluble binary system thin films containing Fe in a magnetic field at temperatures of 200°C or more, causes a sharp increase in coercive force and saturation magnetization. X-ray diffraction of the annealed samples revealed large peaks, which grew larger at increased temperatures, but no such peaks were observed in the control group indicating the rapid formation of Fe clusters. The absence of in-plane anisotropy was verified using X-ray diffraction patterns.

A Study of Amorphous Alloy Cutting Core

The large magnetostriction of iron-base amorphous alloys causes deterioration in magnetic properties during annealing, cutting, and other high-stress processing. The authors formed elliptical wound iron cores using Fe 79 B 16 Si 5 film, annealed them in N 2 gas at 450°C, and impregnated them in epoxy and silicon resins before hardening under various conditions. Measurements of the high-frequency iron loss and AC B-H characteristics indicated an increase in coercive force after impregnation, and a doubling of the iron loss between impregnation and cutting. The original iron loss could be restored by polishing.

Influence of titanium on the mechanical properties of cast specimens of Fe?Cr?Co alloys

1. Alloying with titanium (up to 4%) leads to a significant reduction in plasticity and an increase in hardness and coercive force of Fe−Cr−Co alloys. 2. Fe-26% Cr-12% Co alloy not containing titanium has high plasticity both in the ascast and in the hardened conditions, which makes it possible to cold plastically deform it with a high degree of reduction and preservation of the high magnetic properties.

Surface and near-surface chemical analysis of cobalt-treated iron oxide

A method has been developed for determining the depth profile of Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> and Co in cobalt-treated iron oxides non-destructively using X-ray Photoelectron Spectroscopy (XPS). Cobalt-treated oxides for magnetic recording were prepared from iron oxides containing various levels of Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> . The surface and near-surface layers of these oxides were analyzed by XPS. The Fe and Co 2p and 3s XPS spectra were resolved into multiplet splitting and shake-up components consistent with theoretical calculations and spectra for standard materials. The atomic ratios Co/Fe and Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> /Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+3</sup> were then calculated for the surface and near-surface layers, and compared with those for the bulk sample in order to determine the Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> and Co depth profile. It was found that high Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+2</sup> contents in the near-surface layers and cores of the particles increase diffusion of Co from the surface toward the core. This deeper penetration of cobalt is accompanied by increases in coercive force, magnetic moment, and tape conductivity, but also by higher magnetostriction, poorer print-through, and a broader distribution of particle Hc.

Magnetic ageing characteristics of low silicon electrical steels

Increase is core-loss during the service life of soft magnetic materials is known as ‘magnetic ageing’. This is essentially due to the enhancement of coercive force owing to interaction of domain walls with precipitated carbide particles. Although the effect of silicon at 3 wt% is known, magnetic ageing studies in low-silicon electrical steels are few. This investigation studies through coercive force changes during isothermal ageing the magnetic ageing behaviour of three grades of steel with 0.3, 1.1 and 1.5 wt% silicon, respectively. For steels with 1.1 and 1.5 wt% silicon coercive force increase was slight even after prolonged ageing at low temperatures and initially at higher temperatures. Appreciable magnetic ageing was detected in these two grades at higher temperatures and in the steel with 0.3% silicon at all ageing temperatures. In all three steels the peak increase was larger at lower temperatures and the time required for the peak was longer. While the 0.3% Si-steel indicated sharp coercive force peaks at all ageing temperatures, the behaviour was considerably different for the other two grades. The observations are rationalized on the basis of the type, density and growth rate of precipitated carbides.

省Ｃｏ型・焼結アルニコ磁石合金の研究

An investigation was made of cobalt-saving sintered Alnico magnets by using water-atomized Fe-Ni and Fe-Ni-Cu alloy powders instead of carbonyl Ni powder which was necessary to diffuse in iron powders with Fe-Al alloy powders.(1) Water-atomized Fe-47 Ni powder contained about 0.1% oxygen which was comparatively low. Magnetic properties, by using this alloy powder, became better in shorter sintering time compared with the carbonyl Ni powder.(2) Co addition to this sintered magnet made coercive force (Hc) increase and keep remanence (Br) and sintering density constant. As a result of 6% Co addition, maximum energy product [(BH)max.] was also improved about 20%.(3) An optimum chemical composition of sintered magnet was found to be 27Ni-12Al-4Cu-(3Co)-Fe, when water-atomized Fe-47Ni powder was used. The use of water-atomized Fe-36Ni-5Cu powder instead of it produced in the magnetic properties a little improvement.(4) An optimum sintering temperature and time were 1300°C and more than 3hr respectively in the use of Fe-Ni-(Cu) powder, where higher densification was due to the effect of liquid phase sintering by Fe-50Al (m.p. 1180°C). By applying these sintering conditions, standard magnetic properties were obtained as follows:27Ni-12Al-4Cu-FeBr: 5200G, Hc: 520Oe, (BH)max.: 1.05MGOe27Ni-12Al-4Cu-3Co-FeBr: 5300G, Hc: 600Oe, (BH)max.: 1.20MGOe

Magnetic Properties of Iron and Low Carbon Steel for Soft Magnet Applications

Abstract An investigation was conducted to assess the relative merits of five soft magnet materials proposed as alternatives to ARMCO Electromagnet Iron (EMI), which is no longer available. Four irons and an SAE J403 (1005) (Unified Numbering System [UNS] G10050) steel were considered. When annealed in 94% nitrogen-6% hydrogen at 843°C (1550°F) for 4 h and aged at 100°C (212°F) for 400 h, two of the irons were found to be equivalent to EMI with regard to both coercive force and magnetic stability. A third iron exhibited similar magnetic properties after annealing but required a higher annealing temperature to reduce the coercive force to an acceptable value. The fourth iron and the 1005 steel met the coercive force requirement after annealing at 843°C (1550°F) in 94% nitrogen-6% hydrogen, but suffered significant increases in coercive force during aging at 100°C (212°F).

Magnetic aging characteristics of a phosphorous-bearing low carbon steel

Magnetic aging of steels is essentially the result of an increase in coercive force, inhibition of ferrite domain wall movement by precipitated carbide particles being the main cause of this increase. In the present work, the nature of the carbides precipitating in four grades of electrical steels has been looked into. Existing postulations have been invoked to predict the extent of coercive force enhancement due to metastable (ϵ) and stable (cementite) carbides which have been observed to precipitate in these steels. The model of Drabecki and Wyslocki when applied to the case of metastable carbide predicts its contribution to the coercive force fairly accurately. None of the existing models, however, succeeds in suggesting the extent of the increases accruing from the presence of the stable carbide (cementite) particles. Each of the models takes into account only one or two of the isolated aspects of magnetic interaction between matrix and precipitate. It appears that for cementite, whose several magnetic characteristics are quite different from those of the ferrite matrix, all possible interaction parameters have to be taken into account to determine the actual mechanism.

Displaced hysteresis loop of Cu-Mn-Al alloy

The 44.7Cu-20.6Mn-34.7Al (at. %) alloy, which exhibits a very high coercive force after aging at 300 °C, has been found to show a displaced hysteresis loop when it is cooled to 77 K in a magnetic field. The hysteresis loop of the sample which aged for more than 60 min at 300 °C is shifted along the magnetization axis instead of along the field axis. The magnetization measured at 300 K for a maximum applied field of 15 kOe becomes larger than that at 77 K after aging for 45 min at 300 °C. In the magnetization versus temperature curves of the sample aged for more than 45 min at 300 °C, the magnetization decreases monotonically with decreasing temperature. The increase of coercive force, which is obtained in the sample aged for more than 45 min at 300 °C, corresponds to the increase of the displacement of the hysteresis loop. These magnetic behaviors are considered to be caused by the exchange anisotropy interaction between the regions of ferromagnetic Heusler or Mn-poor phase and ferrimagnetic or antiferromagnetic Mn-rich phase.

Growth-induced anisotropy arising from ordering of transition metal ions in garnets (invited)

The earlier study of the growth-induced anistropy (Ku) in epitaxial YIG produced by the preferential occupation of Ir4+ on octahedral sites has been extended to include most of the transition elements that have degenerate ground states and that can be incorporated in the garnet lattice with the appropriate valence states. Among the 3d elements only Co2+ meets these requirements. For Co2+ charge compensated by Zr4+, Ku increases linearly with the Co/Fe ratio in the melt, reaching 2×105 ergs/cm3 in (111) films for a Co/Fe atomic ratio of 0.17. Among the possible 4d and 5d ions only Ru, Mo, and W are expected to be stable in the desired valence state. Ruthenium yields a large in-plane growth-induced anisotropy (Ku = −1.2×105). Lattice constant, SEM and optical studies indicate that Mo and W have negligible solubility in YIG. For as-grown bubble samples the coercive force (Hc) increase linearly with Ir content, as does Ku. For Ku = 2.3×105, Hc = 70 Oe. The increase of Hc with Ru concentration is substantially smaller. For Ku = −1.2×105, Hc = 2.5 Oe. For YIG (Ir, Ca) samples annealed to reduce Ku (initially 3.5×105) to zero, Hc is 3 Oe, indicating that Ir content alone does not cause the large coercive force. However to data we have not been able to produce an Ir containing material with an easy axis normal and a low value of Hc.

Magnetic properties of Fe-Ni alloys after deformation and annealing

1. With increasing plastic deformation of alloys 36N and 50N, the coercive force and hardness increase, while the saturation induction decreases. Thermal expansion of alloy 36N decreases, while that of alloy 50N remains unchanged. 2. After annealing of deformed alloys 36N and 50N at 200–700°, with furnace cooling, the coercive force and hardness decrease and the saturation induction increases. The thermal expansion coefficient reaches a low point at 300° for alloy 36N but remains unchanged for alloy 50N.

Compatibility of dc and ac magnetic properties of amorphous magnetic materials

This paper reports dc and ac magnetic properties of amorphous Fe40Ni38-Mo4B18 (METGLAS : 2826MB) annealed at various temperatures. DC coercive force showed minimum and squareness ratio reached almost unity annealed at about 350 °C, however, ac permeability turned out extremely low. High permeability has been obtained by annealing above 400 °C at the cost of increase of dc coercive force and decrease of squareness ratio. Nonlinear and hysteretic changes of permeability against ac magnetic field have been observed in materials annealed below 380 °C and as-quenched materials. These defects have been overcome by annealing above 400 °C. Disaccommodations, which are very large in materials annealed below 380 °C, have disappeared also when annealed above 400 °C.

A study of anhysteretic remanent magnetization with the variation of A. C. and D. C. fields on Rajmahal basalts

Anhysteretic Remanent Magnetization is produced in a rock specimen when an alternating field, sufficient to cause saturation. is applied and reduced to zero in the presence of a constant direct field. The ARM produced increase with the increase of A. C. field range when the D. C. field is kept constant and reaches a saturation value. The saturation value is different for different specimens and increases as the coercive force increases. The ARM developed in various specimens with the variation of D. C. field, when the maximum alternating field intensity is constant, is a linear function of a small D.C. field.

Cold-rolling and annealing of amorphous ribbons

Cold-rolling of Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</inf> Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</inf> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> amorphous alloy ribbon results in a large increase in coercive force and a large decrease in magnetization in low fields. It is suggested that these changes are the result of both the sliplike structures developed by the rolling and the strain-magnetostriction induced anisotropy. On annealing the rolled ribbon to temperatures below the crystallization temperature, the magnetic properties recover to the values obtained on annealing as-cast ribbon, but higher temperatures are required. The rolled ribbon showed no evidence for structural changes in high resolution electron micrographs; x-ray and electron diffraction patterns showed no change in the width or position of the diffuse rings; and the glass and crystallization temperatures remained unchanged. However, small angle x-ray scattering showed a decrease in intensity at small angles, and stress relief measurements showed a small increase in the stress-relief rate. Both as-cast and rolled ribbons when annealed even to within a few degrees of the start of crystallization showed no change in the width or position of the diffraction peaks, and no change in the heat of crystallization, glass transition, or crystallization temperature. However, on annealing, the small angle x-ray scattering increased, and stress-relief rate decreased. The change in small angle scattering is qualitatively interpreted as being due to the removal of scattering nuclei on rolling and their development during annealing. The stress relief results are discussed in terms of changes in short-range atomic order.