Permanent Magnet Properties Research Articles

Phase stability of Co<inf>5</inf>Sm

Diffusion couples formed between cobalt and samarium provide useful structures for studying the Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> Sm eutectoid decomposition. The diffusion zones consist of Co, Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</inf> Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> Sm, Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</inf> Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sm, and Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Sm when formed in the 820° to 1130°C range. The absence of the Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> Sm phase in the 775° couple provides supporting evidence for the eutectoid transformation and locates the eutectoid temperature at about 800°C. Couples formed above 820°C and then heat-treated below 800°C provided information on the eutectoid transformation which does not follow the classic Fe-C pearlite reaction. The possible effects of the decomposition on properties of permanent magnets are discussed.

Influence of the Stability of RCo,-Phases on their Permanent Magnetic Properties

Influence of the Stability of RCo,-Phases on their Permanent Magnetic Properties

Permanent-magnet properties of Sm-Ce-Co-Fe-Cu alloys with compositions between 1-5 and 2-17

This paper describes magnetic and metallographic properties of rare-earth-cobalt alloys of (Sm, Ce) (Co, Fe, Cu) z ( 5 \lsim z \lsim 8.5 ). Some alloy compositions exhibit anomalously large coercive forces and have excellent potential for permanent-magnet application. The composition Sm 0.75 Ce 0.25 (Co 0.81 Fe 0.04 Cu 0.15 ) 7.2 shows a maximum energy product of 20.2 MG Oe, which is the highest among the compositions studied. Most alloys exist in the CaCu 5 -type crystal structure although some show a few of very weak superlattice lines characteristic of hexagonal Th 2 Ni 17 . When aged at about 960°C, the alloys show another phase in addition to the aforementioned structures.

Effects of technological factors upon the properties of permanent magnets made from very fine iron powder

1. By producing permanent magnets from a very fine iron powder, it is possible to dispense with the use of expensive and scarce metals such as cobalt, nickel, and copper. 2. Experiments have shown that a powder dried, with continual mixing, in thin layers exposed to a current of air ensures improved magnetic properties. 3. The addition of binder to a wet, washed powder results in a more uniform binder distribution. The presence of a protective binder film on the surfaces of particles reduces the oxidation of the powder and improves the properties of permanent magnet specimens produced from it. 4. Magnets of improved magnetic properties — higher induction, coercive force, and (BH)max value — can be produced from a powder subjected to hydrogen reduction. 5. It is shown that pressing in a magnetic field perpendicular to the direction of the pressing force has the most marked beneficial effect upon the properties of the resultant permanent magnets. The presence of such a field evidently enables the required texture to be preserved during the pressing operation.

Influence of cerium content on the structure and magnetic behavior of Co-Fe-Cu-Ce permanent magnets

As part of a continuing program to understand and optimize the magnetic behavior of Co-Fe-Cu-Ce permanent magnet alloys, we have made studies on the alloy system Co <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.5</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf> CuCe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> with x in the range 0.8 to 1.2. An alloy of x = 1 had previously been studied in detail and found to have good permanent magnet properties. In the present work, it was found that when x > 1, the coercive force was increased while both the Curie temperature and saturation magnetization were decreased. However when x < 1, the coercive force tends to decrease while the Curie temperature and saturation magnetization increase. The increase in coercive force with increase in cerium content can be accounted for largely by the decrease in saturation magnetization. These results are in accord with a domain wall pinning mechanism. Scanning electron microscopy studies have shown that a major second phase in the low cerium alloys is low in copper as compared with the matrix. On the contrary, the copper content of the second phase in the high cerium alloys is larger than that in the matrix.

Magnetic Properties of RCo5 Permanent Magnets Prepared by Liquid Phase Sintering

Results of the experiments on the effects of liquid phase sintering for YCo5, LaCo5, SmCo5, PrCo5 and Sm-Pr-Co series are reported. It is observed that the crystals of an optimum sintering change into a single phase of CaCu5 type. The lattice parameters of RCo5 magnets prepared by the liquid phase sintering process give different unit cell volumes from the base materials. The optimum amount of Co in the sintered Sm-Co alloys was found to be 64.3 wt%. We obtained the best magnetic properties in Sm-Pr-Co series when Sm0.3Pr0.7Co5 was used as a base material.

チルキャストされたCeMM-Cu-Co3元系合金の磁石特性とミクロ組織に及ぼす熱処理の影響について

Sevral works on the cast R-Cu-Co series permanent magnets have already been reported. In this investigation, from the practical standpoint, experiments were carried out for R-Cu-Co ternary alloys which had been oriented by the chilling process. The specimens were heated between 300 and 1200°C for 1 hr in Ar flow, and the variations in magnetic properties, micro-structures, etc, of the specimens furnace cooled or air quenched were investigated. The results are summarized as follows:(1) In the cast state, specimens of the ternary composition (Ce-MM)CuCo4 exhibited the most remarkable chill effect, that is, 4πIr⁄4πI10K=0.96 and (BH)max=5.5 MG·Oe.(2) When compared the furnace cooled specimens with the air quenched specimens for the annealed state, the specimens air-quenched from 500°C showed the most excellent permanent magnet properties, that is, 4πI10K=5450 G, 4πIr=5200 G, IHC=5600 Oe, BHC=3700 Oe, (BH)max=6.0 MG·Oe.(3) The specimens annealed at temperatures above 800°C showed snaky-type hysteresis curves. In the specimens water-quenched from these temperatures, the Ce2Co17 phase as well as the CeCo5 phase was newly detected by X-ray diffraction. This is considered as a cause for these hysteresis curves to precipitate the Ce2Co17 phase.

Sintering of PrCo5magnets with Pr-Co alloy addition

A systematic study of the sintering conditions for PrCo 5 was carried out, using as the liquid-phase sintering aid an alloy that contained 69 weight percent (wt. %) Pr and 29 wt. % Co. The dependence of the permanent-magnet properties on the grinding time of PrCo 5 was evaluated. Different weight ratios of PrCo 5 and the Pr-Co additive were tried and various sintering temperatures and times were studied. It was found that milling time and weight ratio are factors of prime importance for successful sintering. Short milling time and relatively coarse particle size appear to be essential. Magnets sintered under optimum conditions have energy products of nearly 17 MG-Oe, remanence values up to 8500 G, and intrinsic coercive forces up to 9470 Oe. Details of the process and the results are reported.

Variation of the degree of preferential crystallographic orientation and magnetic properties of texturized barium ferrite permanent magnets during sintering

1. A study was made of the effect of sintering temperature on the magnetic properties and demagnetization curves of anisotropic barium ferrite magnets along their texture axis and at right angles to it. 2. It is shown that, during the sintering of texturized barium ferrite, its grains grow in a direction at right angles to the preferential direction of hexagonal axes and that its texture is appreciably improved as a result of grain growth at sintering temperatures above 1220°C. A quantitative evaluation is given of the changes in the degree of texture of such magnets induced by the sintering process. 3. It is demonstrated that the increase in the remanent induction of texturized barium ferrite during sinteringis brought about mainly by an increase in its density at sintering temperatures of up to 1220°C and by an improvement in its texture at temperatures ranging from 1220 to 1300°C. 4. On the basis of an experimentally established relation between the relative coercive force and its absolute magnitude, the hypothesis is put forward that magnetic polarity reversal has a predominantly single-domain character for barium ferrite withIHC > 2900 Oe and a predominantly multidomain character atIHC ≤ 2000 Oe.

Cast Permanent Magnets of the Co5RE Type with Mixtures of Cerium and Samarium

Previous studies of the effect of composition on the magnetic properties of arc-cast alloys in the vicinity of Co3.5CuFe0.5Ce yielded maximum energy products from 4 to 10×106 G Oe, residual inductions from 4000 to 6400 G, and intrinsic coercive forces from 5000 to 12 000 Oe. The partial substitution of samarium for cerium in alloys in this vicinity results in an improvement in permanent magnet properties, with maximum energy products from 4.6 to 12.3×106 G Oe, residual inductions 4300 to 7150 G, and intrinsic coercive forces from 4000 to 13 400 Oe. Freezing points of these alloys were determined using differential thermal analysis. The dependence of magnetic saturation on temperature was determined for several of these alloys from room temperature to 1.5°K. The saturation increases gradually with decreasing temperature without anomaly. The temperature coefficient of saturation magnetization between 25° and −100°C was found to be 0.1%/°C for the alloy Co3.5CuFe0.5Ce, 0.06%/°C for the alloy Co3.5Cu1.35Fe0.4Sm. Intermediate values were obtained for mixtures of Ce and Sm. The temperature coefficient of saturation magnetization was reduced to practically zero by the partial substitution of Gd for Ce.

COBALT-SAMARIUM PERMANENT MAGNETS PREPARED BY LIQUID PHASE SINTERING

The preparation and measurement of magnetic properties of cobalt-samarium permanent magnets prepared by liquid-phase sintering are discussed. Energy products in excess of 15×106 G Oe were observed. Long time exposure to air at 150°C did not degrade the samples.

Tempering of high-coercivity Alnico alloys

1. The standard and multistage tempering of Alnico alloys (Magnico and Ticonal) ordinarily used is not the optimal treatment for obtaining the highest magnetic properties of permanent magnets. The magnetic properties (coercive force and maximum magnetic energy) are inversely proportional to the temperature of stepped tempering with optimal holding times (particularly at elevated tempering temperatures). 2. From the time of attaining the maximum coercive force at different tempering temperatures it is possible to plot a temperature—time diagram that gives the tempering conditions to ensure the highest magnetic properties for any Alnico alloy.

Some relationships between crystal textures and magnetic properties of alnico 8

Some relationships between crystal textures and their permanent magnet properties are reviewed on the basis of a homogeneous uniaxial anisotropic ferromagnet and a mosaic grain agglomerate in the commercial size of an Alnico 8 alloy. From the results obtained, it has been concluded that the highest energy might be obtained by control of the following two factors (besides the ordinary ones of composition, casting, and heat treatment): 1) the mean deviation angle of crystal axis should be within 18° of the magnetization direction; 2) the crystal grain should be below 3 pcs/10 mm along the magnet length.

Influence of elastic stress on precipitation and magnetic properties of Fe-Ni-Al alloys

External elastic stress applied during the precipitation process of Fe-Ni-Al alloys influences the orientation of elongated precipitates. Compression of the crystal along the \langle 100 \rangle axis makes the orientation of elongated precipitates to this direction unfavorable. When compressive stress is applied along the \langle 110 \rangle axis, the rod-like precipitates are oriented mostly to \langle 100 \rangle axis which is perpendicular to the direction of compression. Uniaxial magnetic anisotropy induced during the thermomechanical treatment (cooling under stress) causes a considerable increase of permanent magnetic properties in comparison with those obtained without stress. The energy product BH_{\max} = 2.1 \times 10^{6} G.Oe is obtained on a single crystal of alloy free from cobalt.

Effect of Processing on Permanent Magnet Materials Containing Rare-Earth Metals

It is established that the new rare-earth permanent magnet alloys containing copper show precipitation effects during heat treatment. Alloys drastically quenched from a high temperature had a comparatively low value of coercive force which increased substantially upon aging at a lower temperature. Also, upon aging, it was observed optically that a precipitate formed. These effects permit considerable latitude in the heat treatment of the alloys. Experiments on coarse powders showed that useful permanent magnet properties can be obtained with alloys in this form. Oriented coarse powder compacts which are stable in air having intrinsic coercive forces at 17 000 Oe have been made.

Preparation of SmCo5 Permanent Magnets

The technology of making SmCo5 magnets with energy products of 20 × 106 GOe is described. This technology consists of the preparation of a powder by grinding, aligning the powder particles in a magnetic field, and cold pressing by applying a uniaxial deformation at 20 kbar. The permanent magnetic properties of the SmCo5 powders are shown to vary appreciably with various applied chemical treatments and with the composition of the alloy. The intrinsic coercive force appears to decrease with time but remains so large that the demagnetization of the induction is hardly affected. Some properties of the magnets are discussed.

Study of Co-Fe-V Permanent Magnet alloys (vicalloys)

The historical development of Co-Fe-V permanent magnet alloys (vicalloys), their technological importance and scientific study, are reviewed. The basic, as yet unsolved, problem of the origin of their magnetic hardness is examined. Results of recent work employing Mossbauer spectroscopy and magnetic measurements at different temperatures, as well as some X-ray and electron-optical analysis, are presented and discussed. Mossbauer spectroscopy established the fact that vicalloy in the permanent magnet state is composed of two phases: ordered ferromagnetic α′ (bcc, ferrite) and paramagnetic γ (fcc, austenite). Samples quenched from the high temperature γ field consist almost entirely of retained austenite. However, on cooling to cryogenic temperatures (liquid and solid nitrogen, 60 to 80 ° K), or by cold work, some of it is transformed irreversibly into disordered ferromagnetic α. This is confirmed by magnetic measurements in the cryogenic range; the results were inconsistent with a previously postulated model based on a reversible paramagnetic γ to ferromagnetic γ transition or on some superparamagnetic process. The measurements, when correlated with Mossbauer data, confirm that the phase transition is not accompanied by any change in iron content of the phases. An interesting change in magnetic anisotropy of flat, thin samples following cold-work and heat-treatment for optimum permanent magnet properties was confirmed by Mossbauer spectroscopy. X-ray diffraction confirmed the above findings on the phase structure of vicalloy and no direct evidence was found for a third metastable phase, intermediate between α and γ, which was proposed by Henkel to account for the magnetic hardness of vicalloy. However, one unidentified diffraction line in the X-ray pattern of optimum heat-treated vicalloy calls for more attention to this postulate. Electron microscopic results did not remove the existing ambiguity as to the role of shape anisotropy in promoting magnetic hardness of vicalloy. On the other hand, a possible contribution by crystalline anisotropy is suggested by some electron diffraction patterns.

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.

Forming structure and magnetic properties of Alnico VS55 alloys

Some results of explorations on crystallographic structure perfection of Alnico VS55 single crystals are presented. Segregation and block disorientation in crystals are shown to have some influence on the process of spinodal decomposition in a magnetic field, and on permanent magnet properties.

New Permanent Magnet Materials Containing Rare-Earth Metals

Previously, most basic magnetic properties of the hexagonal intermetallic compounds involving the rare-earth (RE) and 3-d transition elements were reported in the literature. In addition, some of these compounds were investigated by various workers for permanent magnet properties by grinding ingots of the compounds into very fine powder. Recently, we discovered new permanent magnet materials which were based mostly on the hexagonal intermetallic compounds Co5RE. Replacement of cobalt with copper in some of these rare-earth compounds resulted in solid materials having substantial permanent magnet properties. An outstanding feature of these alloys is their high value of intrinsic coercive force. High-energy product alloys were found in the Co5−xCuxSm and Co5−xCoxCe systems with iron additions. Small pieces of Co3.5Fe0.4Cu1.35Sm exhibited BR=6450 G, BHC=4000 Oe, and (BH)m=9×105 G Oe. Also, small pieces of Co3.5Fe0.5CuCe exhibited BR=5100 G, BHC=3500 Oe, and (BH)m=5.2×106 G Oe. In general, these alloys are prepared by inert-electrode arc melting, resulting in a relatively rapid freezing from the molten state. The samples are then given a low-temperature anneal. Cross sections of the specimens show microstructural directionality which is a result of freezing in a direction normal to the cold surface of the hearth. These directional effects appear to be associated with the directional magnetic properties that are important because of the high crystal anisotropy of the alloys. When a specimen of the composition Co3.45Fe0.25Cu1.35Sm was annealed at 1100°C and examined by optical-microscope and electron-probe techniques, particles rich in Co5Sm were observed to be embedded in a Cu5Sm-rich matrix. The iron appeared largely in the cobalt-rich phase. The cobalt-rich particles were approximately 2.5×10 μ. Further work is in progress to improve directional properties and thus further improve the magnetic properties.