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Magnetics, IEEE Transactions on

Issue 2 • Date June 1970

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Displaying Results 1 - 25 of 97
  • [Front cover and table of contents]

    Publication Year: 1970 , Page(s): 0
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  • Introduction to the second European conference on hard magnetic materials

    Publication Year: 1970 , Page(s): 152
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  • Magnetism of rare earth alloys

    Publication Year: 1970 , Page(s): 153 - 157
    Cited by:  Papers (3)
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    The main properties of the rare earth elements are discussed, emphasizing their magnetic properties. However, it is difficult to use these elements in practice, because their Curie points are located below room temperature. In order to take advantage of the properties of these substances, they can be alloyed with iron, cobalt, or nickel. The properties of the rare earth-cobalt alloys are discussed, the phase diagram and the crystal structures are described, and the ferrimagnetic behavior is explained. Alloys of interest for magnet applications are selected. View full abstract»

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  • Sublattice magnetization and cation distribution in BaMg2Fe16O27(Mg2W) ferrite

    Publication Year: 1970 , Page(s): 158 - 161
    Cited by:  Papers (4)
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    Mössbauer measurements were carried out in compound BaMg2Fe16O27(Mg2W) by utilizing both polycrystalline and single-crystal samples. The resonant γ-absorption spectra have been measured with the absorbers at temperatures of 85 to 800°K and in some cases in the presence of a 15-kOe external magnetic field. The values of the hyperfine magnetic fields Hhfat the Fe57nuclei in the different sublattices as functions of temperature have been measured. By fitting the curve of the saturation magnetization σ versus temperature, the cation distribution over the available lattice sites has been deduced. From the value of σ extrapolated at 0°K, it turns out that the number of Bohr magnetons (n_{B})W per elementary cell is higher than the value obtained by adding the corresponding values for the S and M structures. The Curie temperature of the compounds has also been measured and is equal to (440 ± 5)°C. View full abstract»

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  • On the state and distribution of iron in the alnico 8 alloy

    Publication Year: 1970 , Page(s): 161 - 163
    Cited by:  Papers (1)
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    Mössbauer measurements have been carried out on Alnico 8 alloy after various heat treatments. The spectrum measured at room temperature (RT) of the sample heat treated for optimum permanent-magnet characteristics shows the presence of Fe in paramagnetic environment, with an average quadrupolar splitting Δ = 0.16 mm/s probably due to tetragonal distortion of the matrix. For the sample quenched and aged for 111 hours at 650°C the spectra measured at temperatures close to RT clearly show that the Curie point of the matrix is very near to RT. The obtained results allow us to interpret the behavior of saturation magnetization σ of the alloy as a function of the aging temperature. From Mössbauer measurements carried out on overaged samples the homogeneity characteristics of the phases are inferred. View full abstract»

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  • Alternating and rotational hysteresis losses of γ-Fe2O3powders in a nonmagnetic matrix

    Publication Year: 1970 , Page(s): 164 - 166
    Cited by:  Papers (6)
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    Some aspects of the alternating and rotational hysteresis losses of very diluted samples of γ-Fe2O3particles are examined. The packing fraction p of the particles ranges from 0.001 to 0.120. The coercive force is found to be independent of p . The alternating and rotational hysteresis losses appear dependent upon p for p < 0.04 ; the rotational losses increase considerably as p approaches zero. The values of the rotational hysteresis integral are close to the theoretical ones corresponding to the model of magnetization reversal of chain of spheres with fanning, but they increase slightly with decreasing p for p < 0.04 . Generally, the ratio of rotational to alternating losses is about twice that for bulk materials. All these effects are ascribed to a weakening of the magnetic interactions among particles. View full abstract»

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  • On the origin of oblique-incidence anisotropy in evaporated cobalt films

    Publication Year: 1970 , Page(s): 167 - 169
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    The main results obtained when studying a temperature dependence of the uniaxial anisotropy of oblique-incidence magnetic films of cobalt are given. It has been stated that when depositing the films onto a substratum heated to 350°C, the easy magnetization axis (EA) is perpendicular to the incidence plane of a molecular beam (a positive anisotropy). EA is in the incidence plane (a negative anisotropy) when the temperature of a substratum is 60 to 80°C. At intermediate temperatures of a substratum a positive anisotropy arises at small angles of deposition and a negative one is at great angles of deposition. Temperature dependences of the constant of the uniaxial anisotropy for samples with a positive or negative anisotropy distinguish between each other. In samples with a positive anisotropy this constant changes with the temperature as a square of magnetization; in samples with a negative anisotropy at less than room temperatures, this constant is approximately proportional to the anisotropy constant of a massive-cobalt single crystal. The obtained results have been considered from the theoretical point of view, and it has been concluded that a negative anisotropy in oblique-incidence films arises as a result of formation of very small grains stretching in the direction of the incidence plane and having a significant anisotropy of the magnetic energy in layers adjoining the boundaries (the Néel anisotropy). Observation of the typical temperature dependence of the anisotropy constant of these samples is a very convincing proof of existence of the Néel anisotropy. View full abstract»

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  • Rotational hysteresis in ticonal alloy

    Publication Year: 1970 , Page(s): 169 - 172
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    Anisotropy constants and rotational hysteresis have been investigated at different stages of optimal heat treatment on 8-mm-diameter spherical samples. The changes in the uniaxial anisotropy constant obtained upon tempering are in good agreement with the respective changes in coercive force. Rotational hysteresis has been measured in the range from 400 to 28 800 Oe. Two maxima have been obtained on the curves of the rotational hysteresis versus field after all heat treatments. The first maximum is interpreted in terms of reversal magnetization of single-domain precipitates in a low magnetic matrix. The nature of the second maximum is not clear. View full abstract»

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  • Magnetization and remagnetization of anisotrophic magnetically hard ferrites

    Publication Year: 1970 , Page(s): 172 - 177
    Cited by:  Papers (5)
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    Magnetization curves and hysteresis loops of anisotropic hard ferrites were analyzed after the specimens had been demagnetized either thermally or by an ac field parallel or perpendicular to the preferred axis (PA) between -196°C and Curie temperature, or by a dc field. Each demagnetization yields a specific magnetization curve; below saturation fields, asymmetrically positioned and noncentrosymmetrical loops develop, except after ac demagnetization at 20°C (=measuring temperature) parallel to PA. This is due to domain configurations differently arranged and of different stability. The asymmetry is caused by "frozen" unstable configurations, which undergo an irreversible change due to the action of the field. Therefore, with reversed field not all of the previous possibilities for remagnetization are still available. View full abstract»

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  • The influence of magnetic reversal on the magnetic stiffness of polycrystalline barium ferrite

    Publication Year: 1970 , Page(s): 177 - 179
    Cited by:  Papers (1)
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    The magnetic stiffness of polycrystalline isotropic barium ferrite has been measured in the region of negative field strength. It is found that the Stoner-Wohlfarth model describes magnetic reversal only for small field strength. Irreversible magnetization processes known from magnetization measurements have strong influence on the field dependence of the magnetic stiffness. The domain splitting of "90° crystallites" which was found in previous investigations proves to be essentially independent of the magnetic history of the sample. View full abstract»

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  • Coercivity and wall motion

    Publication Year: 1970 , Page(s): 179 - 181
    Cited by:  Papers (2)
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    The process of magnetization reversal in ferromagnets with uniaxial crystal anisotropy is discussed. It is shown that the "critical-size concept" has no relevance to coercivity. Critical fields are distinguished as nucleation fields and propagation, or pinning, fields. The pinning of walls is discussed and illustrated by experiments on various substances. Intrinsic pinning in highly anisotropic materials is predicted. View full abstract»

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  • The recent development of permanent magnet materials containing rare earth metals

    Publication Year: 1970 , Page(s): 182 - 190
    Cited by:  Papers (10)
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    The prospect that permanent magnets with previously unattainable coercivities and energy products might be made from cobalt-rare earth alloys has caused intense research efforts in the last three years. Alternative ways of preparing magnets from powders and by casting were demonstrated in several laboratories. (BH)_{\max } \approx 20 MG.Oe andM H_{c} > 25 000 Oe have been achieved with SmCo5, and the development of manufacturing processes for magnets made from this alloy has begun. This paper reviews the basic concepts, properties of the alloys of interest, and the physical factors influencing the coercive force. Approaches to alloy, powder, and magnet fabrication are discussed, with their merits and drawbacks; also problems incurred in the materials development and their possible solutions. Application areas are reviewed and some economic factors considered. It is concluded that the R Co5magnets are indeed beginning to live up to their promise, but that more materials research, process development, and circuit redesign are needed if their potential is to be fully utilized. View full abstract»

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  • The structure of Ni-Co-Al-Ti-Cu-Fe permanent magnets

    Publication Year: 1970 , Page(s): 191 - 194
    Cited by:  Papers (2)
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    A technique has been developed for extracting one of the phases present in Ni-Co-Al-Ti-Cu-Fe permanent magnet alloys heat-treated to give optimum magnetic properties. Examination of such extracts by electron microscopy and electron-probe microanalysis has confirmed previously held theories that the precipitate is strongly magnetic (50 percent Fe and 50 percent Co) in a virtually nonmagnetic matrix. The results show that for permanent magnets containing 5-percent Ti the matrix has the same structure ( L2_{1} ) as a range of materials known as Heusler alloys. View full abstract»

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  • Magnetic properties of alnico 5 and alnico 8 phases at the sequential stages of heat treatment in a field

    Publication Year: 1970 , Page(s): 194 - 198
    Cited by:  Papers (2)
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    The results of an investigation of the magnetic properties of the α' and α phases in Alnico 8 and Alnico 5 alloys are presented. The influence on the alloy magnetic characteristics of changing these properties during the process of heat treatment is discussed. View full abstract»

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  • Experiments on RCO5and related compounds with permanent magnet properties

    Publication Year: 1970 , Page(s): 198 - 201
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    This paper investigates the possibility of replacing the expensive rare-earth metals by the relatively inexpensive cerium mischmetal in rare-earth-cobalt permanent magnets. Using mischmetal, it is possible to obtain powders with coercivities as high as when pure cerium or lanthanum are used, although it is not possible to equal the values obtained with samarium. A compact with a density of 5.3 g.cm-3gives a (BH)_{\max } of 3.1 MG.Oe, and if the special methods for obtaining high densities used by Buschow et al. or by Das were applied there seems no reason why values exceeding 10 MG-Oe should not be obtained. There are, however, some rather peculiar changes which occur in the compacts, especially when they are heated to about 150°C. It is not possible simply to replace cerium by mischmetal in the solid alloys of cobalt-cerium-copper described by Nesbitt as the response to heat treatment is quite different. View full abstract»

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  • The effect of cobalt, sulfur, and tellurium on the liquidus-solidus gaps of Fe-Ni-Al-Co-Ti alloys

    Publication Year: 1970 , Page(s): 201 - 204
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    The values of liquidus and solidus temperatures were measured for various permanent magnet alloys including Alcomax III and Hycomax II, III, and IV. The effect of sulfur on these temperatures was studied for each of the alloys, and the effect of tellurium on the temperatures for Hycomax IV was also studied. The effect of liquidus-solidus gaps on columnar crystal formation is discussed. An attempt is made to relate the values found to those obtained from equilibrium diagrams. View full abstract»

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  • On some peculiarities of the curves sigma versus temperature on alni and alnico alloys

    Publication Year: 1970 , Page(s): 205 - 207
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    The curves σ = f(T) are taken at a very high heating rate (1000°C/min) on samples of Alni, Alnico 5, and Alnico 8 alloys, heat treated so that their equilibrium state should correspond to a temperature of about 600°C and the α' phase particles should be much bigger than after a usual heat treatment. The Curie point occurs respectively at 760, 905, and 920°C. As we think we have avoided the diffusion process between α' and α phases, the Curie points should be those of the α' phase in almost optimal permanent magnet conditions. From that it is possible to argue that in the Alni alloy the α' phase is not pure Fe, but also includes Al and Ni; in Alnico 5 and Alnico 8 alloys, on the other hand, the ferromagnetic phase is not only Fe-Co, but also includes Al or Ni or both. In other curves taken at lower rates (300°C/min) on samples with normal morphology we observed a hysteresis of about 20-30°C between the Curie points during heating and cooling, which may be eventually ascribed to the gap between the solution and spinodal decomposition temperatures. View full abstract»

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  • The temperature dependence of the domain structure of uniaxial single crystals with high-anisotropy field

    Publication Year: 1970 , Page(s): 207 - 210
    Cited by:  Papers (2)
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    The temperature dependence of the domain structure of single crystals of uniaxial ferrimagnetic oxides with high-anisotropy field in the SrO( 6 - x )Fe2O3 x Al2O3compositional series, with x = 1.8 and 2.4, was investigated. The domain configurations of thermally and/or ac field demagnetized states and the changes in dc and ac fields were observed by means of the colloid technique using a suspension in paraffine oil. The temperature dependence of the wall energy density between room temperature and the Curie point (270°C) of the compound with x = 1.8 was computed using the temperature dependence of the saturation magnetization and the domain width for the Kittel-like domain structure. It has been found that the room temperature domain structure of the compound with x = 2.4 depends upon the mode of demagnetization, i.e., thermally or in the ac field. The ac demagnetized states are more stable than the thermally demagnetized ones. The samples exhibit a room temperature memory of the previous magnetization, which decreases with rising temperature. This memory is completely lost after heating at 400°C. The peculiarities of the temperature dependence of the domain structure and magnetic behavior on thermal cycling are explained by considering the existence of magnetic inhomogeneities within the crystal. View full abstract»

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  • Structural changes in alnico alloys

    Publication Year: 1970 , Page(s): 211 - 214
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    The solid solution decomposition of Alnico 5 and Alnico 8 is studied by means of electron microscopy and X-rays. The following sequence of the decomposition process is found: Alnico 5: spherical zones-periodic modulated structure-rod-shaped particles of metastable tetragonal phases-final cubic phases; Alnico 8: the same sequence, but due to great importance of elastic energy at the decomposition, the three-dimensional modulated structure forms even during sharp quenching. The kinetics of modulated structure formation is studied. It is shown that the modulation wavelength increases according to a (time)nlaw. The activation energies of the decomposition process are determined. The spinodal mechanism of decomposition of the alloys in question is discussed. View full abstract»

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  • X-ray and Mössbauer study of alnico 8

    Publication Year: 1970 , Page(s): 215 - 217
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    Mössbauer spectroscopy and X-ray studies have been used to investigate two Alnico 8 alloys in different stages of a thermomagnetic treatment cycle. It is revealed that the first low-temperature aging subsequent to magnetic field hardening results in redistribution of components among the alloy phases, while the second low-temperature aging causes the variation in the degree of weak magnetic phase order. The temperature range of developing effective magnetic fields on iron nuclei in the α phase is shown to lower with an increase in the degree of Fe3Al-type order. View full abstract»

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  • Some relationships between crystal textures and magnetic properties of alnico 8

    Publication Year: 1970 , Page(s): 218 - 220
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    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. View full abstract»

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  • Physical metallurgy and magnetic measurements of SmCo5-SmCu5alloys

    Publication Year: 1970 , Page(s): 221 - 224
    Cited by:  Papers (6)
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    The magnetic properties of the hexagonal intermetallic compounds involving the rare-earth and 3d transition metals have been reported in the literature. These alloys look promising as fine-particle permanent magnets. A large number of samples in the system SmCo5-xCuxwere prepared by induction melting under a protective atmosphere, and annealed at various temperatures. An outstanding feature of these alloys is their high intrinsic coercive force. After annealing at low temperatures, they show coercive forces above 20 kOe and an energy product of about 8 × 106G.Oe. The most important factors determining the coercive force appear to be the chemical composition, the cooling rate, the alignment of the SmCO5-rich phase, and the annealing treatment. Examination by electron microscopy and electron probe techniques suggests a spinodal decomposition of a supersaturated solid solution into two phases, one rich in SmCo5and the other rich in SmCu5. View full abstract»

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  • Investigations of high-coercivity alnico alloys

    Publication Year: 1970 , Page(s): 225 - 230
    Cited by:  Papers (2)
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    For Alnico alloys containing 32-42 percent Co, 0-9 percent Ti, 6-8 percent Al, 14 percent Ni, 3 percent Cu, 0-0.5 percent S, 0-2 percent Nb, remainder Fe, the liquidus and solidus temperatures and the upper limit of the (α + γ) phase field were determined. The greatest influence is exerted by titanium in that all temperatures decrease as the Ti content increases. The influence of cobalt on temperature is considerably smaller, while sulfur has no influence at all. The addition of 2 percent Nb resulted only in the upper limit of the (α + γ) phase field being shifted to temperatures 20 to 30°C lower. Alnico alloys containing about 39 percent Co and 7-8 percent Ti were brought to columnar crystallization by controlled cooling, using a seed crystal. The seed contained 6 percent Ti and the lowering speed was between 0.50 and 3.75 cm/h. At a lowering speed of 0.50 cm/h and a temperature gradient of 5 to 10°C/mm, it was possible to obtain columnar crystallization without using a seed. The following magnetic values were obtained: (BH)_{\max } = 11.0-11.7 MG.Oe,B H_{c} = 1780-2100 Oe, B_{r} = 8920-10 050 gauss. View full abstract»

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  • Relations between structure and properties in magnetically hard Fe-Co-V alloys: Deficiencies of equilibrium diagrams

    Publication Year: 1970 , Page(s): 230 - 232
    Cited by:  Papers (2)
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    First Page of the Article
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  • On a new mechanism of periodical distribution of the inclusions in the high-coercivity alloys

    Publication Year: 1970 , Page(s): 233 - 236
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    A theoretical analysis of elastic and surface energy of a cubic solid solution which disintegrates into two isomorphic cubic phases has been carried out. It is shown that in such a solution the formation of periodically distributed thin plate inclusions is energetically advantageous. View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology