Showing papers on "Coercivity published in 1970"
TL;DR: In this article, the magnetic structures of high-coercive-force Co-Cr composite films were analyzed using magnetostatically coupled domains and a saw-toothed structure was observed.
Abstract: Electron microscopy was used to analyze the crystallographic and magnetic structures of high-coercive-force Co-Cr composite films. The chromium sublayer appears to give high coercive forces by causing the growth of cobalt in the hexagonal phase with a relatively narrow distribution of grain sizes. Magnetization reversal was examined by Lorentz microscopy of films with coercive fields up to H_{c} = 900 Oe. It proceeds by nucleation and extension of magnetostatically coupled domains. The progressive limitation of these extensions as the coercive force increases illustrates the connection between the magnetostatic coupling, the coercive force, and the squareness of the hysteresis loop. Lorentz microscopy was also used to investigate a recorded transition between NRZ 1 and 0 states and showed a saw-toothed structure, characteristic of a magnetization in the plane of the film.
119 citations
TL;DR: In this paper, a relation between the reversible susceptibility χ of the minor loops and the coercivity Hc has been found, showing that the investigated material is determined by the pinning of domain walls, rather than nucleation.
Abstract: Measurements of minor loops of SmCo5 powders have revealed that wall motion is predominant in the magnetization process. A relation between the reversible susceptibility χ of the minor loops and the coercivity Hc has been found, showing that the coercivity of the investigated material is determined by the pinning of domain walls, rather than nucleation. The relation χHc2 = constant has been found in a wide range of coercivities obtained by aging of the material. The aging process is interpreted as a decrease of the density of pinning sites, each site retaining its pinning force. The influence of hydrogen on Hc, which is reported recently, is interpreted likewise. A hysteresis loop measured on a single particle of a few microns size confirms these interpretations and allows for a refined model of pinned‐wall coercivity of SmCo5 powders. A full account will be submitted as a regular article to this Journal.
68 citations
TL;DR: In this article, the authors have shown that the coercive force is very closely related to and can be profoundly influenced by the nature of the particle surface, and that the long-range prospects of these materials may well be related to the improvement of the properties of compounds other than SmCo5 by influencing the factors that control the magnetization reversal process.
Abstract: Since the discovery of the extremely high magnetocrystalline anisotropy of YCo5 in 1966 there has been rapidly increasing interest in the development of cobalt‐rare‐earth intermetallic compounds as permanent magnet materials. The observed coercive forces are still only a small fraction of the anisotropy fields, and for some reason the coercive forces attainable with SmCo5 are larger than in other isostructural compounds with comparable anisotropy fields. A number of experiments have shown that the coercive force is very closely related to and can be profoundly influenced by the nature of the particle surface. The processing of these materials into magnets can be approached in several different ways, with due regard to the problem of chemical stability. The long‐range prospects of these materials may well be related to the improvement of the properties of compounds other than SmCo5 by influencing the factors that control the magnetization reversal process.
68 citations
TL;DR: In this paper, the influence of certain heat treatments on the coercivity of SmCo 5 was investigated and a model, accounting for the high coercivity was proposed, which is based on pinning rather than on nucleation of domain walls.
67 citations
TL;DR: The magnetic properties of the hexagonal intermetallic compounds involving the rare-earth and 3D transition metals have been reported in the literature as mentioned in this paper, and the most important factors determining the coercive force appear to be the chemical composition, the cooling rate, the alignment of the SmCO 5 -rich phase, and the annealing treatment.
Abstract: 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 SmCo 5-x Cu x were 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 SmCO 5 -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 SmCo 5 and the other rich in SmCu 5 .
55 citations
TL;DR: In this paper, the process of magnetization reversal in ferromagnets with uniaxial crystal anisotropy is discussed and it is shown that the "critical-size concept" has no relevance to coercivity.
Abstract: 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.
47 citations
Patent•
IBM1
TL;DR: In this paper, high coercivity metallic magnetic material in finely divided particle form is milled with a lubricant to convert it to a leafing flake, which is then mixed with a suitable binder vehicle and solvent and coated on a non-magnetic substrate to form a leafed coating in which most of the magnetic flakes float to the surface of the vehicle.
Abstract: High coercivity metallic magnetic material in finely divided particle form is milled with a lubricant to convert it to a leafing flake. The flakes thus obtained are mixed with a suitable binder vehicle and solvent and coated on a non-magnetic substrate to form a leafed coating in which most of the magnetic flakes float to the surface of the vehicle to form a relatively continuous thin layer of high coercivity magnetic material. When the binder vehicle is dried or cured it firmly adheres the thin layer of magnetic material to the substrate and also provides adhesion between the flakes of magnetic material to thus provide a wear and corrosion resistant magnetic recording media capable of high resolution recording.
46 citations
TL;DR: In this article, a selfconsistent iterative approach was used to calculate the demagnetization in an isolated recorded transition between two areas of opposite magnetization, as a function of the coercivity, remanence, and thickness of the recording medium.
Abstract: Various theoretical approaches have been recently offered to describe the writing and demagnetization processes in magnetic recording. All invariably correlate their calculations with readback pulse measurements, thus clouding their results with the dominant readback losses. In this paper a self‐consistent iterative approach was used to calculate the demagnetization in an isolated recorded transition between two areas of opposite magnetization, as a function of the coercivity, remanence, and thickness of the recording medium. Lorentz transmission microscopy was used to verify the predictions of the theoretical calculations. For this purpose, a series of thin magnetic films of different magnetic properties and thicknesses were prepared and then recorded with an inductive‐type transducer. The magnetization transition regions were observed to resemble a sawtooth structure. The walls of the sawtooth were inclined towards the easy magnetization direction, and the magnetization on either side of these walls was...
44 citations
TL;DR: In this article, the magnetic, magneto-optic, and optical properties of thin films of MnBi prepared in the quenched high-temperature phase have been measured.
Abstract: Magnetic, magneto‐optic, and optical properties of thin films of MnBi prepared in the quenched high‐temperature phase have been measured. The saturation magnetization is reduced from normal phase by 23% and the coercive force is more than doubled at room temperature. In the visible spectrum region, there is no significant change in the optical absorption, but the strong wavelength dependence of the magneto‐optic Faraday rotation in the normal films is essentially eliminated. At the 6327‐A HeNe‐laser wavelength the room‐temperature Faraday rotation is reduced to one‐half of that of the normal films. These properties coupled with the low Curie temperature of 180°C make the quenched MnBi films well suited for optical memory applications. Experimental results of laser Curie‐point writing, erasing, and reading using the quenched films have been obtained. In comparing with the normal films, the laser writing power is reduced by a factor of four; unheated spots are not disturbed by the erasure field; and the margin between the writing temperature and the decomposition temperature is much increased. The measured activation energy and annealing time constant associated with the transformation of this high‐temperature phase to the normal phase indicates that the thermal stability of the quenched MnBi films is lacking for memory applications.
41 citations
TL;DR: In this article, the coercive force ratio of MnFe 2 O 4 and Co-Fe 2 o 4 is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K 1 of sintered ferrites.
Abstract: Investigations of the formation and magnetic properties of Mn δ Co 1-δ Fe 2 O 4 formed in alkaline aqueous solution by the coprecipitation method are covered. The lattice constant of these ferrites apparently reduced with decreasing average particle size below about 500 A. The coercive force ratio of MnFe 2 O 4 and Co-Fe 2 O 4 is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K 1 of sintered ferrites. As the average particle size became larger, the coercive force and the apparent remanence increased linearly, and superparamagnetic critical size was determined. The sizes range, for example, from 50 to 100 A for CoFe 2 O 4 and from 150 to 200 A. for MnFe 2 O 4 . From the correlation between the average particle size and their magnetization, the limit size of ferromagnetic critical particle was also determined. Results obtained in this experiment are approximately in accord with Neel's Version of the theory on thermal fluctuation aftereffect of magnetic fine particles.
41 citations
TL;DR: In this article, the yttrium iron garnet sintering and grain growth rates were determined as a function of the ytrium/iron ratio, which was interpreted as a result of the oxygen content variation through the garnet field.
Abstract: Sintering and grain-growth rates were determined for yttrium iron garnet as a function of the yttrium/iron ratio. Rates decreased with an increase in this ratio; this behavior is interpreted as a result of the oxygen content variation through the garnet field. For constant sintering time, density and grain size, as well as microstructure-dependent properties, varied through the garnet field. Remanent magnetization and coercive force in particular depended on composition and sintering temperature. The rf field for nonlinear spin-wave excitation, hcrit, measured for dense samples with grain sizes from ∼4 to 30 μm, varied by a factor of four.
TL;DR: In this paper, a simple method of determining intrinsic coercivity distributions in aligned assemblies of uniaxial particles is given, and the results show that reliable comparisons of the observed intrinsic coer-civities and the theoretical estimates must be made using the coercivity distribution obtained at the lowest possible temperatures.
Abstract: A simple method of determining intrinsic coercivity distributions in aligned assemblies of uniaxial particles is given. It is shown that the measured intrinsic coercivity, Hc, is not a suitable parameter for comparison with the theoretical estimates. The coercivity, H,., and the remanence coercivity, HR, of both the intermetallic compounds SmCo5, and LaCo5, show a strong linear temperature dependence. Both parameters increase as the tempera-ture is decreased. The results show that reliable comparisons of the observed intrinsic coer-civities and the theoretical estimates must be made using the coercivity distributions obtained at the lowest possible temperatures.
TL;DR: In this article, the magnetic deformation transforms the cobalt from fcc to hcp and the coercive force increases with increasing growth rate, reaching 330 Oe at 2.1×10−1 cm/sec.
Abstract: Directional solidification of Au–Co eutectic produces an aligned array of fcc cobalt rods in a gold matrix. The cobalt becomes finer, but more lamellar, as growth rate increases. Intrinsic coercive force increases with increasing growth rate, reaching 330 Oe at 2.1×10−1 cm/sec. Coercive forces up to 925 Oe are produced by subsequent wire drawing. Analysis of the magnetization curves indicates that deformation transforms the cobalt from fcc to hcp.
TL;DR: In this article, Barium ferrite (Ba.0.6Fe 2 O 3 ) platelets were extracted from the crystailized glass by leaching the matrix in acetic acid.
Abstract: Barium ferrite (Ba.0.6Fe 2 O 3 ) platelets of approximately \frac{1}{2}\mu m diameter and with intrinsic coercive force of about 5000 Oe were crystallized from a glass phase. To study the nature of the defects and their influence on the magnetic properties, the crystailized glass was plastically deformed by applying a pressure of 30 kbar in an opposed anvil press. Barium ferrite platelets were extracted from the crystailized glass by leaching the matrix in acetic acid. Magnetic measurements indicated 1 to 2 percent increase in saturation magnetization and about 40 percent decrease in coercive force in the deformed platelets compared to the properties in the undeformed platelets. Transmission electron microscopy revealed deformation twins, nonbasal slip, and stacking faults in the deformed platelets. In another experiment, the platelets after leaching the matrix were deformed at 30-kbar pressure. Saturation magnetization decreased by 9 percent and coercive force by 55 percent. The results are discussed by comparing with the changes in properties obtained in ball milled powders. Annealing the deformed powders resulted in partial recovery of saturation magnetization and coercive force to the original undeformed state.
TL;DR: In this paper, two sets of dense kiln-fired lithium ferrite ceramic bodies with 4πMs around 3600 and around 2600 G, respectively, have been prepared with low microwave dielectric losses (tan δ < 0.0005) and high remanence ratios (Br/4πMs = 0.7).
Abstract: Two sets of dense kiln‐fired lithium ferrite ceramic bodies with 4πMs around 3600 and around 2600 G, respectively, have been prepared with low microwave dielectric losses (tan δ < 0.0005) and high remanence ratios (Br/4πMs = 0.7). These low dielectric losses were obtained by addition of MnO2. For samples which were thicker than 0.25 cm, an anneal in an oxygen atmosphere was required. The lower 4πMs compositions were obtained by substituting titania for part of the iron oxide in the basic lithium ferrite formulation. A number of physical properties were evaluated and the results are presented. These include density 4πMs and Curie temperature. In addition, properties useful for microwave latching applications such as complex dielectric constant and hysteresis characteristics, i.e., ramanent magnetization and coercive force are presented. The temperature variation of the hysteresis properties for selected compositions is also shown.
TL;DR: In this article, the mean coercivities of subbasalt from the Mid-Atlantic Ridge were investigated and the authors showed that the coercivity of sub-basalt samples from the Median Valley of the Ridge is stable.
Abstract: The mean coercivities of natural (n.r.m.), anhysteretic (a.r.m.), and isothermal (i.r.m.) remanent magnetization in 34 samples of submarine basalt from the Mid-Atlantic Ridge are 270, 250, and 370 oersteds respectively, showing their magnetization to be stable. The spectra of coercive force of n.r.m. and a.r.m. of these basalts are similar, although, because of small secondary components, there are small differences in the low coercive force range (0 to 100 Oe). The magnitude and sign of these differences are used to derive an empirical relationship between coercivity and the magnitude of secondary components, and to infer the polarity of primary components. The inferred polarities of samples from within the Median Valley of the Ridge are all normal, whereas both normal and reversed polarities are found from the adjacent mountains and plateaus. Experiments show that warming specimens from the Median Valley to 100 °C for 90 h causes the production of a new component with a lower intensity, and higher block...
TL;DR: In this article, the authors describe some of the structure-property relations for Co and CoNi films containing Group VIB additions, i.e., chromium, molybdenum, and tungsten and Group VA additions, such as phosphorus, arsenic, antimony, and bismuth.
Abstract: This paper describes some of the structure-property relations for Co and CoNi films containing Group VIB additions, i.e., chromium, molybdenum, and tungsten and Group VA additions, i.e., phosphorus, arsenic, antimony, and bismuth. All films were prepared by electrodeposition. The magnetic properties and metallurgical structure of the films with tungsten cover the same range of parameters as produced with the phosphorus films. The quantity of the elements required to achieve the maximum in coercive force increases substantially in the sequence P, As, Sb, and Bi; and in the sequence W, Mo, and Cr. The saturation moment and coercive force both decrease with increase of the concentration of added element required to attain the maximum coercive force. The quantity of the elements required is believed to be related to the ability of the electrolyte to produce a refinement of the grain size of the deposit, and the ability of the element added to segregate to the grain boundaries. The saturation moments of Co with W and P agree with the results expected for solid solutions except at high concentrations. The structure sensitive magnetic properties obtained with CoNiW films are qualitatively interpreted in the same way as for the CoNiP films, i.e., on the basis of a strongly interacting array of fine particles. The alloys containing Cr, Mo, or W possess improved resistance to aging at elevated temperatures and in corrosive environments.
Patent•
18 Nov 1970TL;DR: Magnetic latches and switches based on the flux cancellation or flux diversion principle use the high coercive force of cobaltrare earth permanent magnets such as cobalt-samarium as discussed by the authors.
Abstract: Magnetic latches and switches based on the flux cancellation or flux diversion principle use the high coercive force of cobaltrare earth permanent magnets such as cobalt-samarium. These permanent magnets are not demagnetized by a flux cancellation coil and can be made thin in the field direction. Devices with thin magnetic circuits and low volume armature achieve high unlatching speeds.
TL;DR: In this article, the magnetization of the platelets is described by three parameters, i.e., the ratio of diameter to thickness with the easy axis perpendicular to the surface.
Abstract: The coercive force of fine‐particle magnets consisting of hard ferrite particles in a nonmagnetic matrix is always considerably less than 2K/IS. A coherent rotation model is not adequate to describe this behavior. It is suggested that reversed domains come into existence at places where strong stray fields are present. Plate‐shaped particles are considered with a large ratio of diameter to thickness with the easy axis perpendicular to the surface. At the edge the magnetization is forced to incline due to the large horizontal component of the stray field. The magnetization of the platelets is described by three parameters. Numerical minimization of the total energy, which is carried out for BaFe12O19 and SmCo5, shows that at a certain field, Hn, an antiparallel oriented domain comes into existence. Hn is positive (parallel to the initial magnetization direction) for particle thicknesses d>1.5 μ for BaFe12O19 and for d>1.8 μ for SmCo5. For d<345 A (BaFe12O19) coherent rotation becomes energetically more fav...
TL;DR: The magnetic properties of CrTe films relevant to magneto-optic memory applications were studied in this article, where the polar remanence ratio was 0.2 and the coercive field decreased with the magnetization and vanished at the Curie temperature.
Abstract: A study was made of the magnetic properties of CrTe films relevant to magneto‐optic memory applications. Polar‐Faraday rotation measurements in the visible and near infrared were taken on CrTe films prepared by sequential deposition of layers of Cr–Te–Cr on cleaved mica substrates. The Faraday rotation and absorption decreased respectively from 0.5×105°/cm at 0.55 μm to 0.4×105°/cm at 1 μm and 2×105 cm−1 at 0.5 μm to 0.6×105 cm−1 at 2.5 μm. The rotation and coercive field decreased with the magnetization and vanished at the Curie temperature (∼70°C). The polar remanence ratio was 0.2. An in‐plane magnetization curve had a remanence ratio of 0.8, a saturation induction (4πMs) of 1015 G and a coercive field of 117 Oe. The measurements indicate significant advantages for CrTe films in memory applications if the epitaxial growth can be improved resulting in higher polar remanence.
TL;DR: In this paper, the authors measured the coercivity of isolated defects in nearly perfect crystals and developed models of spin configurations near twin and grain boundaries in the presence and absence of magnetic domain walls to explain the observed coercivities.
Abstract: Twin and grain boundaries impede the motion of magnetic domain walls in the orthoferrites. Bubbles distort and collapse before it is possible to propagate them through twin boundaries and all but very low angle grain boundaries. A new experimental technique has been used to measure the coercivity of isolated defects in nearly perfect crystals. The coercivity measured is the minimum applied field required to force a planar domain wall past a defect. Models of the spin configurations near twin and grain boundaries in the presence and absence of magnetic domain walls have been developed to explain the observed coercivities.
TL;DR: In this paper, the authors show that the magnetization process within the basal plane of natural crystals of hematite is more complex, and that the susceptibility anisotropy is related primarily to the low coercivity fraction of the remanent moment.
Abstract: Measurements of room temperature susceptibility in the basal plane of natural single crystals of α‐Fe2O3 in which a high field isothermal remanence has been induced reveal a substantial anisotropy whose minimum is coincident with the direction of remanence. The susceptibility anisotropy appears to be related primarily to the low coercivity fraction of the remanent moment. Sizeable discontinuous changes in the susceptibility are sometimes present as the specimen is rotated. Recent domain wall studies have disclosed the presence in synthetic crystals of 180° walls exclusively. The present work suggests that the magnetization process within the basal plane of natural crystals of hematite is more complex.
TL;DR: In this article, high temperature annealing of thin polished plates of rare-earth orthoferrites has been found to be highly effective in reducing the coercivity resulting from mechanical processing.
Abstract: High temperature annealing of thin polished plates of rare-earth orthoferrites has been found highly effective in reducing the coercivity resulting from mechanical processing. The annealing atmosphere must be oxygen or an oxygen-inert gas mixture free of reactive contaminants such as water vapor, carbon dioxide, and platinum oxide. Chemical reactions through contact of orthoferrite with other materials must be avoided. Annealing below 1000°C relieves elastic and plastic surface strains and is characterized by an activation energy of 5.8 × 103cal/mole or 0.25 eV/molecule. Temperatures near 1500°C are required to remove brittle fracture damage. High temperature annealing may also be effective in reducing the coercivity caused by some bulk defects. The annealing process is capable of producing high quality orthoferrite plates suitable for domain propagation devices.
TL;DR: In this article, the design and construction of an apparatus for domain observation and for the measurement of magneto-optic rotation and coercivity of thin magnetic films, by means of the Faraday effect, are described.
Abstract: The design and construction of an apparatus for domain observation and for the measurement of magneto‐optic rotation and coercivity of thin magnetic films, by means of the Faraday effect, are described. A spatial resolution of 5 μ is achieved, allowing scanning of magneto‐optic properties across the film. Gas flow cooling and heating of the samples result in a temperature range of −120 to +200°C. A special sampling detector allows continuous recording of magneto‐optic rotation and coercivity as a function of temperature and wavelength.
TL;DR: In this article, the authors used ion milling to remove abrasive and polishing induced defects and at the same time produce flat surfaces of much less than 1 mil in thickness, which is useful for memory and logic circuits.
Abstract: Magnetic oxide platelets, useful for memory and logic circuits, are presently prepared by diamond abrasive polishing techniques. Processed platelets, however, usually contain thin damage layers and microscopic scratches resulting in increased domain wall coercivity. Platelets less than 1 mil in thickness and of desirable flatness are difficult to prepare using these techniques. Ion milling has been successfully used to rapidly remove abrasive and polishing induced defects and at the same time produce flat surfaces of much less than 1 mil in thickness. The measured removal rate was 0.5 μ/h/side; however 500‐μ/h/side rates are attainable. Final platelets are scratch free, flat, and highly reflecting, having lower domain wall coercivity than diamond polished plates. No change in mobility was observed following ion milling. The process is adaptable to large areas and a wide variety of related applications.
TL;DR: In this article, an 85 Co-12Fe-3Nb wire, 0.5 mm in diam., subjected to a sequence of a 1100°C intermediate anneal, 90% cold reduction and 750°C aging is deemed best for reed switch applications.
Abstract: Ductile alloys of the Co–Fe–Nb system in the vicinity of 90% Co were studied for reed switch applications. Wires have been investigated which have high values of coercive force, squareness ratio and remanence as well as high stability of these magnetic properties against heating. As a result of this research, an 85 Co–12Fe–3Nb wire, 0.5 mm in diam., subjected to a sequence of a 1100°C intermediate anneal, 90% cold reduction and 750°C aging is deemed best for this application. This wire shows a coercive force of 20 Oe, a squareness ratio of 0.95 and a remanence of 15 000 G. Intermetallic Co–Nb compounds precipitate during aging treatment. This phenomenon causes the coercive force to increase. The cold drawing facilitates the precipitation. The intermediate anneal temperature should be sufficiently high to realize a complete solid solution in the wire. The drawn wire has 〈111〉 fiber texture. Since 〈111〉 is an easy magnetization direction, the wire shows a good rectangular hysteresis loop along the axis. Thi...
Patent•
28 Dec 1970
TL;DR: In this article, the authors used a MAGNETICULAR IRON OXIDE PARTICLES MODIFIED with SMALL AMOUNTS of COBALT oxide to achieve higher coerciveness.
Abstract: MAGNETIC RECORDING TAPE HAVING A COATING OF ORIENTED MAGNETIZABLE PARTICLES IN A BINDER AFFORDING SUPERIOR ABILITY TO STORE HIGH FREQUENCY INFORMATION BY VIRTUE OF ORIENTED MAGNETIZABLE ACICULAR IRON OXIDE PARTICLES MODIFIED WITH SMALL AMOUNTS OF COBALT OXIDE, WHICH IRON OXIDE PARTICLES COMPRISE GAMMA-FE2O3. AT APPROXIMATELY TWO PARTS BY WEIGHT PER ONE PART OF BINDER AND PHYSICALLY ALIGNED, THE NOVEL PARTICLES PROVIDE IN THE ALIGNED DIRECTION A COERCIVITY HC EXCEEDING 350 OERSTEDS AND A BR EXCEEDING 800 GAUSS. HIGHER COERCIVITY MAY BE ATTAINED BY CONTROLLING THE HEATING STEPS IN MAKING THE NOVEL PARTICLES TO PROVIDE UP TO ABOUT 25% FEO BY WEIGHT OF THE TOTAL IRON OXIDE.
IBM1
TL;DR: In this article, the coherent rotation model of magnetization reversal is applied to crystallographically cubic films of gadolinium iron garnet chemically deposited on yttrium aluminum garnet (YAG) substrates.
Abstract: The coherent rotation model of magnetization reversal is applied to crystallographically cubic films magetized perpendicularly to the film plane. The model is used to predict the hysteretic properties of single crystal films of gadolinium iron garnet chemically deposited on yttrium aluminum garnet (YAG) substrates. Included in the analysis is the magnetoelastic coupling resulting from the induced in-plane strain in the film. By substituting Tb for Gd ions in the iron garnet, the magnetoelastic coupling can be used to control the coercive field for the [111]-oriented films and the remanence ratio for [100]-oriented films. The application of these films to magnetothermal recording using a polar Faraday effect for readout is discussed.
Patent•
26 Aug 1970
TL;DR: In this article, a magnetic material having particle cores of arbitrary configuration, the surface of which is coated with a layer of a ferromagnetic metal or alloy such as of Co or Ni or the like, having high coercive force and high magnetic flux density.
Abstract: This invention relates to a magnetic material having particle cores of arbitrary configuration, the surface of which is coated with a layer of a ferromagnetic metal or alloy such as of Co or Ni or the like, having high coercive force and high magnetic flux density. When the particle cores are spicular, the spicular shape is maintained after the deposition of the ferromagnetic metals. The properties of the ferromagnetic material thus obtained are improved by heat treatment and are excellently usable as a magnetic recording medium and permanent magnets. The method of preparing the material comprises dispersing the particles in a solution containing metallic ions, heating the solution in a H2 atmosphere at high pressures and heat-treating the resultant precipitate.
TL;DR: In this article, the dependence of coercivity, squareness, and uniaxial anisotropy of thin metallic films on thickness was studied, with the angle of incidence of the vapor flux as a parameter.
Abstract: Magnetic hardness in thin metallic films has been sought and achieved by a number of different techniques, including oblique incidence evaporation in a vacuum. Previous studies of oblique incidence evaporation of Permalloy and iron have shown that the easy axis rotates from a direction transverse to the plane of incidence to a direction parallel to the plane of incidence, at an angle of deposition θ=65° with respect to the substrate normal. In this paper we studied the dependence of coercivity, squareness, and uniaxial anisotropy of iron films on thickness (100–1500 A), with the angle of incidence of the vapor flux as a parameter (θ=40°–85°). We found that at all angles of incidence studied, the coercivity increases with increasing thickness, reaching a peak at about 400 A, and decreasing monotonically for larger thickness. The uniaxial anisotropy in the transverse direction reaches a peak for θ=55°, while for θ>65° the uniaxial anisotropy in the parallel direction predominates, and increases rapidly with...