Showing papers in "IEEE Transactions on Magnetics in 1984"

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

Abstract: Structural and metallographic studies were carried out on the Nd-Fe-B alloy system as well as the Nd-Fe-B tetragonal compound on which record high energy magnets have been developed using a powder metallurgical technique. The study on the new magnet has also been extended to other R-Fe-B componds containing various rare earths (R) and to R-Fe-Co-B alloys. The results are as follows; (1) The sintered Nd-Fe-B magnet is composed of mainly three phases, the Nd 2 Fe 14 B matrix phase plus Nd-rich phase and B-rich phase ∼ Nd 2 Fe 7 B 6 ) as minor phases. (2) Nd 2 Fe 14 B has the space group of P4 2 /mnm. The crystal structure of this phase can be described as a layer structure with alternate stacking sequence of a Nd-rich layer and a sheet formed only by Fe atoms. The sheet of Fe atoms has a structure similar to the σ-phase found in Fe-Cr and Fe-Mo systems. (3) The Nd-rich phase containing more than 95 at.% Nd, 3∼5 at.% Fe and a trace of B has fcc structure with a=0.52 nm. This phase is formed around grain boundaries of the matrix phase. Nd 2 Fe 7 B 6 phase has an one-dimentional incommensurate structure with a=a o and c\simeq8 C o , based on a tetragonal structure with a o =0.716 nm and c o =0.391 nm. (4) In the as sintered Nd 15 Fe 77 B 8 alloy periodic strain contrasts are observed along grain boundaries, which disappear after annealing at 870K. This may be related to the enhancement of the intrinsic coercivity of the sintered magnet by post sintering heat treatment. (5) Stable R 2 Fe 14 B phases are formed by various rare earths except La. Of all the R 2 Fe 14 B compounds, Nd 2 Fe 14 B has the maximum saturation magnetization as high as 1.57 T. Dy and Tb form R 2 Fe 14 B phases with the highest anisotropies. Small additions of these elements greatly enhance the coercive force of the Nd 2 Fe 14 B base magnet. (6) Partial replacement of Fe by Co raises the Curie temperature of the Nd 2 Fe 14 B compound, which improves the temperature coefficient of the remanence of the magnet. But the intrinsic coercive force is decreased by the Co addition.

3D analytical calculation of the forces exerted between two cuboidal magnets

Abstract: The interaction forces exerted between permanent magnets are used in many magneto-mechanical devices (magnetic bearings, couplings, etc...). By analytical calculation, 2D problems can be solved easily, when simple shaped magnets are used. Usually, the 3D problems are numerically computed, by using a finite element method for example. This paper presents the 3D calculation of the interaction forces exerted between two cuboidal magnets, by analytical means only. The obtained expressions are rather complicated, but a pocket programmable calculator is sufficient to the force calculation. By derivation, the analytical expressions of the stiffnesses can be easily obtained. In addition, the 3D analytical calculation allows a simple optimization of the magnet dimensions.

Finite element implementation of virtual work principle for magnetic or electric force and torque computation

Abstract: In a recent paper [1], we described a methodology for the numerical evaluation of global magnetic or electric force and torque acting on a movable part of an electromagnetic device. The method is based on application of virtual work principle. Force and torque are obtained as the derivatives of the energy versus the displacement of the moving part. The paper [1] was essentially theoritical. In the present paper, we give more practical informations about the implementation of the method in a finite element context and illustrate it by a 3D application.

Perpendicular magnetic recording -- Evolution and future

Abstract: This paper reviews research results for the head, medium and recording properties of a perpendicular recording system. Superior bit density characteristics obtained so far indicate that perpendicular recording is basically free from demagnetization in the high density region and that it will establish a new field of recording technology in the future. The prediction is explained in the context of complementary profiles of longitudinal and perpendicular recording. At the very beginning of magnetic recording, a perpendicular-type head was considered but abandoned because a suitable medium did not exist. Progress in material science has enabled us to develop a perpendicular recording medium which is very well suited for ultra high density recording. As so often happens, history has repeated itself through another study of perpendicular recording.

Review on recent advances in the field of amorphous-metal sensors and transducers

Abstract: Recent researches and developments of applications of amorphous ribbons and wires to sensors and transducers are reviewed. Various sensitive and quick response magnetic sensors with very small amorphous cores have been developed corresponding to strong demands in the fields of information devices, automobiles, power motor drives, industrial robots, and industrial measurement instruments. Relationship between amorphous material properties and the suitable applications to sensors and transducers, the basic principle of amorphous sensor constitutions, and the advantageous points of amorphous sensors are represented.

Recent developments of non-oriented electrical steel sheets

Abstract: The iron loss improvement which produces the highest grade of non-oriented Si steel is described on the basis of studies which clarify the effects of Si content, grain diameter, impurities and crystalline texture on the iron loss. Impurities were found to increase iron loss directly through magnetic domains and indirectly through grain diameter and crystalline texture. The progress of clean steel producing technology resulted in extreme reduction of core loss.

Planar inductor

Abstract: As the first step for developing magnetic I.C, planar inductors have been investigated. Planar inductor, which does not require conventional winding, consists of planar coil and two magnetic films which sandwich the coil. Design parameters have been obtained for four types of planar inductors, hoop type, spiral type, meander type and closed type. We fabricated a hoop type and a meander type planar inductor. The inductance of the hoop type was about 40 nH at 1 MHz, and showed flatness up to 10 MHz. In the meander type, the inductance was about 100 nH at 1 MHz, and showed a flat response till 40 MHz.

Synthesis of iron-nitride films by means of ion beam deposition

Abstract: Thin films of various iron nitride compounds have been deposited by using the ion beam deposition system with a new sputtering type of ion source and the dependence of their crystal structure and magnetic properties on preparation conditions has been investigated. Crystal structure and magnetic properties of the films depend significantly not only on substrate temperature Ts and nitrogen partial pressure P N2 but also on the arrival energy of the depositing ions. The films of multi phase, of α-Fe, γ'-Fe 4 N and a unknown phase, with large saturation magnetization 4πMs about 24 kG are obtained by adjusting Ts, P N2 and the ion accelerating voltage Vp at 200\sim250\deg C, 1.5\sim2.0\times10^{-5} Torr and 20 V, respectively. Coercive force Hc of the films with large 4πMs decreases against an increase of 4πMs and is rather low about 1 Oe. These results indicate that the iron nitride films with large saturation magnetization and low coercive force deposited by the ion beam deposition system could be used in a thin film type of magnetic head for high density recording.

Basic principles of coaxial launch technology

Abstract: Coaxial launchers have received very much less attention than railguns because of their greater complexity, but they offer several significant advantages. They require no physical contact with the projectile, scale readily to very large diameter, can distribute thrust over the length of the projectile, have more adaptable energy supply and impedance requirements (being a multi-turn device), offer higher efficiency, positive control over the launch cycle, and permit component redundancy to achieve any desired degree of reliability. Thrust for a given current can be a hundred times higher than in a railgun, but the current must be synchronized with projectile motion. The voltage required to do so increases with velocity, and high voltage commutation capability represents the technological limit to launch velocity. Present research activity is concerned with commutation in the low and high velocity domains, position sensing techniques, dynamic stress containment in drive coils, and design of the first practical EM launcher: a Nimitz class aircraft catapult.

Erasable magneto-optical recording media

Abstract: Magneto-optical storage techniques in amorphous metal films have the advantages of high bit density and contactless write, read and erasure operations. Digital information is stored as a sequence of small magnetic domains; writing and erasure is performed by local temperature rise (AlGaAs laser heating) in combination with a low external magnetic field. In principle, the number of switching cycles is unlimited. Non destructive readout is achieved via magneto-optical effects. Material and system aspects for erasable compact-disk audio application will be reviewed. Disks are vapour-deposited on pregrooved substrates. Binary and ternary alloys of Gd, Tb combined wlth Fe,Co are highly suitable, storage media. For practical use bi- and multilayer structures were used in order to improve the read-out efficiency and lifetime of the disk. Aging effects were studied by measurements of magneto-optical and magnetic properties and SIMS analysis during the lifetime of the disk. Current results of about 45 dB CNR (30 kHz bandwidth) and a lifetime for the disk of more than 5 years opens the discussion of applications in low- and high-density storage in professional and consumer fields.

Magnetocrystalline anisotropy and phase transformation in Co-Pt alloy

Abstract: A magnetic characterization of the CO 1-x Pt x system with 0\leqx\leq0.8 has been made. The anisotropy field (H A ) of both the hard magnetic phases, i.e. hexagonal at low Pt content and tetragonal around the equiatomic composition, has been measured by the singular point detection technique (SPD). The dependence of H A on composition and temperature is given. The solid state transformation diagram at low Pt content has been completed by using the thermomagnetic analysis (TMA).

Electromagnetic wave absorber using ferrite absorbing material dispersed with short metal fibers

Abstract: A broad band electromagnetic wave absorber in GHz frequency range was newly developed by two-layer construction. Each layer operates as a low-impedance resonator and an impedance transformer. For the low-impedance resonator design, a ferrite/resin mixture incorporated with short metal fibers is used. The electromagnetic wave absorber presented in this paper has a broader operation bandwidth, nearly 50 % in relative bandwidth (bandwidth more than 20 dB absorption/center frequency), than the operation bandwidth for a conventional ferrite absorber. Broadband characteristics are achieved in oblique incidence, up to nearly 45 degrees of incident angle.

Organic resin method for highly reactive and homogeneous hexaferrite powders

Abstract: Hexagonal ferrites with M, Y and W structures were prepared from powders obtained by the decomposition of organometallic salt (citrate) solidified solutions, Due to the improved reactivity of these powders with respect to the classical ceramic ones, a number of advantages were obtained: pure hexaferrites were produced at lower temperature; they exhibited improved magnetization and coercitivity; a finer and more homogeneous granulometry was achieved in the final products. X-Ray diffractometry, magnetic analysis and SEM microscope observations were used for characterizing the obtained materials.

The electromagnetic levitation and guidance technology of the 'transrapid' test facility Emsland

Abstract: A large scale test facility for the high speed ground transportation system TRANSRAPID has been built in Emsland. In the near future this test facility will show the economic feasibility of such a system. An essential component of this system is the magnetic levitation and guidance system of the vehicle. The requirements on this suspension system are: good ride comfort, high reliability and low operating costs. The elements of the suspension system are controlled cross field electromagnets with massive iron cores and rails for guidance and controlled longitudinal field magnets with a laminated iron core and rail for levitation. The reason for lamination is the combination of three operating tasks in the levitation magnets. These are: levitation, propulsion, and inductive power transfer to the vehicle. These magnets generate the exciting field of the synchronous linear motor. Due to these tasks the theoretical model for a levitation magnet has to be expanded in order to be able to describe these effects in dynamic simulations. The mechanical and the electrical structure of the suspension system must have several redundancies in order to get a high overall safety.

Improved method for the investigation of the rotational magnetization process in electrical steel sheets

Abstract: The magnetization processes in electrical steel sheets in rotating and alternating magnetic fields up to 1.8 T can be investigated with an instrument which is described in this paper. The components of the vectors of the magnetic induction \vec{B} and the magnetic field strength \vec{H} are measured wlth four sensors during one period and processed by a transient recorder and a computer. Some results for rotating fields are presented for a sample of non-oriented silicon steel.

Co-Cr perpendicular magnetic recording tape by vacuum deposition

Abstract: The relation between the incident angle and the crystallographic orientation of a vacuum deposited Co-Cr film is discussed. Also presented are the magnetic properties and the orientation of both a Ni-Fe underlayer and the Co-Cr film for the double layer medium, and the experimental results about the composition distribution in the co-cr film. The films were deposited on a transporting polymer substrate by continuous vacuum deposition. It is found that the orientation of the Co-Cr film is determined only by the incident angle at the initial point of the film formation, and that deposition efficiency more than 50% can be achieved easily. A double layer medium with Ti film under the Ni-Fe film (Co-Cr/Ni-Fe/Ti medium), which is suitable for perpendicular magnetic recording, is produced by vacuum deposition. Auger depth profile in radial direction of the column of the Co-Cr film shows directly that there is Cr segregation near the columnar grain boundaries.

Effect of stress on the magnetostriction and magnetization of single crystal Tb .27 Dy .73 Fe 2

Abstract: The magnetostrictive properties of single crystal Tb .27 Dy .73 Fe 2 was examined under compressive loads up to 48 MP a. Magnetostrictions > 1.8 × 10-3were observed for stresses greater than 20 MPa. Magnetization and magnetostriction were calculated for the magnetization rotation model, which was extended to include cubic anisotropy and compressive loading along the [111] axis. The effect of a distribution of magnetic moment directions is discussed.

Columnar structure and some properties of metal-evaporated tape

Abstract: Metal Evaporated Video Tape (ME Tape) has been developed for highly competitive and innovative mass-produced VTRs. A magnetic recording layer of Co-Ni film of 0.15 μm was prepared by vacuum roll coating technology in an oxygen atmosphere using polyester substrate. The shape of the columnar grains forming the film is influenced by this deposition system which has a continuously varied incidence and deposition rate. The anisotropic columnar structures and properties of the ME Tape were investigated. The magnetic properties of a series of films made by varying the minimum incident angle were investigated and the results of the magnetic anisotropies and different recording characteristics of different tape transport directions are presented here. On the other hand, the still-frame life and the frictional behavior of ME Tape has shown no anisotropies for tape transport.

Jitter-less pulse generator elements using amorphous bistable wires

Abstract: New jitter-less pulse generator elements are presented using amorphous magnetostrictive wires. These elements induce sharp voltage pulses with ∼ 6V/cm2.Oe.turn due to the large Barkhausen jumps and with ∼ 6V/cm3.Oe due to the Matteucci effect using external ac fields of more than 0.1 Oe at frequencies between 0.01 Hz - 10 k Hz. Jitter of the pulse inducing phase is less than 1/10 and the pulse height is about twice that of Wiegand wires, respectively. The critical field of the large Barkhausen jump is controlled by heat treatment, etching, or twisting the wires. These wires are expected to be useful for high-performance pulse generator elements for high resolution rotary encorders by combining them with magnet ring, torque sensors, proximity sensors and magnetometers.

Recent advances of bismuth garnet materials research for bubble and magneto-optical applications

Abstract: Epitaxially grown bismuth-substituted iron garnet films of composition R 3-x Bi x Fe 5-y M y O 12 with x \leq 2.5 (R=Y,Gd,Lu,Yb and M = Al,Ga,Si) are considered with respect to the temperature and concentration dependence of their magnetic and magneto-optical properties. In particular, the magnetization, Curie temperature, uniaxial anisotropy, optical absorption and Faraday rotation reveal pronounced changes with increasing bismuth content. Special attention is paid to the control of the uniaxial growth-induced anisotropy caused by the ordering of the bismuth ions via the site preference mechanism. This ordering process is characterized by a strong dependence on the growth conditions such as the melt composition and the supercooling allowing the variation of K\min{u}\max{g} in the range O Jm-3. The magneto-optical properties exhibit a linear increase with increasing bismuth content.

Torque transducers with stress-sensitive amorphous ribbons of chevron-pattern

Abstract: In this paper, a simplified assembling method is presented by which a reliable and compact torque transducer exhibiting wide dynamic range and good linearity is obtained. The only modification applied to the shaft to obtain the torque transducer is to glue several pairs of stress-sensitive amorphous ribbons of rectangular form or of parallelogram form to the shaft in a chevron-pattern. Experiments are carried out on torque transducers with the nonmagnetic torsion bar to comfirm the theoretical prediction and with the magnetic steel torsion bar to examine the output characteristics and the dynamic response.

Electrical and thermal modeling of railguns

Abstract: Electrical and thermal modeling of railguns at Los Alamos has been done for two purposes: (1) to obtain detailed information about the behavior of specific railgun components such as the rails, and (2) to predict overall performance of railgun tests. Detailed electrical and thermal modeling has concentrated on calculations of the inductance and surface current distribution of long parallel conductors in the high-frequency limit and on calculations of current and thermal diffusion in rails. Inductance calculations for various rail cross sections and for magnetic flux compression generators (MFCG) have been done. Inductance and current distribution results were compared with experimental measurements. Two-dimensional calculations of current and thermal diffusion in rail cross sections have been done; predictions of rail heating and melting as a function of rail size and total current have been made. An overall performance model of a railgun and power supply has been developed and used to design tests at Los Alamos. The lumped-parameter circuit model uses results from the detailed inductance and current diffusion calculations along with other circuit component models to predict rail current and projectile acceleration, velocity, and position as a function of time.

Particle-size effects on the switching behavior of uniaxial and multiaxial magnetic recording materials

Abstract: The coercivity of a magnetic material is a well-defined parameter only if the time-scale of interest is specified. A measurement that produces rapid changes of magnetization will yield a higher value of the coercivity than one that operates on a longer time-scale. The difference is due to the thermally-assisted nature of the magnetic switching process. Thus, for a magnetic recording material, the coercivity relevant to high-frequency writing will be greater than that relevant to demagnetization processes (such as transition broadening) during long-term storage. The discrepancy between the two values will become more pronounced as the volume of the magnetic switching unit becomes smaller; this effect is relevant to the question of the ultimate information densities achievable by magnetic media. The "writing coercivity" and the "storage coercivity" can be estimated from typical magnetic measurements and simple kinetic theory, for both uniaxial and multiaxial ("isotropic") recording materials.

The micromagnetics of thin-film disk recording tracks

Abstract: This paper, for the first time, illustrates the details of the recorded tracks of thin film disks written with film heads flying 1600-2600 A above the disk surfaces. The magnetic medium was a thin film of Fe-Co-Cr alloy with a Mrt of 2.8-2.9×10-3emu/cm2and a coercivity of 450-490 Oe. Readback signals were carefully taken from the tracks. They were then studied micromagnetically using ferrofluid decoration and Lorentz electron microscopy techniques. The bit pattern was essentially a series of isolated single domains with alternate magnetization along the circumferential direction of the disk. The transition zone consisted of sawtooth shaped, head-on domain walls. Bit shift, readback signal asymmetry, and the amplitude modulation due to overwrite were directly observed on the tracks microscopically. It was concluded that these phenomena could be related to the writability of the head with respect to the media.

Crystallographic and magnetic investigation on W-type-hexaferrite single crystals in the solid solution series SrZn 2-x Co x Fe 16 O 27

Abstract: The saturation magnetization and the magnetocrystalline anisotropy were measured on single crystals in the solid solution series SrZn 2-x Co x Fe 16 O 27 (SrZn 2-x Co x -W) at 298 K and 6 K Lattice constants and Curie-temperatures are also given as a function of the composition The magnetocrystalline anisotropy changes from uniaxial to planar dependent on temperature and cobalt substitution at x \approx 05 for 6 K and x \approx 085 for 298 K The six-fold anisotropy in the basal plane of the planar W-hexaferrites increases strongly with increasing cobalt content Crystals with a low Co substitution (x = 033 and 067) have an anomalous discontinuity in their hard direction magnetization curves; indicating a first-order magnetization process

Nonlinear complex finite elements analysis of electromagnetic field in steady-state AC devices

Abstract: A nonlinear analysis of electromagnetic devices supplied by a sinusoidal alternating current or voltage source is presented. In numerous apparatus like motors, generators, traveling field induction furnaces, etc., the saturation effect must be taken into account for the design but does not affect widely the waveform of the current which may be assumed sinusoidal. We shall present here a complex analysis based on the assumption of sinusoidal fields on two-dimensional geometries in Cartesian or axisymmetric coordinates.

Ampere tension in electric conductors

Abstract: It is shown that the application of the Ampere and Lorentz force laws to a closed current in a metallic circuit results in two different mechanical force distributions around the circuit. In addition to the transverse forces, which both laws predict, the Ampere electrodynamics requires a set of longitudinal forces that subject the conductor to tension. These longitudinal forces explain electromagnetic jet propulsion and the recoil mechanism in a railgun. Pulse current experiments are described in which Ampere tension shattered solid aluminum wires. Electrons moving through the metal lattice are the basic current-elements of the Lorentz force theory. But Ampere assumed his current-elements to be infinitely divisible. With the help of computer-aided analysis and experiment, it is demonstrated that the amperian current-element must also be of finite size and involve at least one lattice ion in addition to the conduction electron. Calculations with Ampere's formula have been found to give reasonable results when the atom, or unit atomic cell, is taken to be the smallest possible current-element. Some technological consequences of Ampere tension are discussed briefly with regard to pulse currents in normal conductors and steady currents in superconductors. The use of large macroscopic current-elements of unit length-to-width ratio gives rough approximations to the Ampere tension. The accuracy of the calculations can be improved by resolving the conductor into a number of parallel filaments, each filament being subdivided into cubic current-elements.

Magnetic filtration of ultra-fine particles

Abstract: The status of the generalised HGMS theory, which describes the capture of ultra-fine particles, is reviewed and new results concerning the effect of hydrodynamic interactions between the particles are presented. Recent experiments leading to the development of a new class of separating devices are also reviewed.

Multiple stage pulsed induction acceleration

Abstract: Pulsed induction is an acceleration mechanism based on the repulsive force exerted on a conductor magnetically coupled with a pulse coil. Because this process is inductive no direct mechanical or electrical connection with the projectile is required. It has resulted in the highest acceleration ever achieved: 2 gram ring to 5 km/s in 1 cm length by Bondaletov, USSR. In principle this process can be extended by multi-staging to produce even higher velocities at increased efficiencies. We have modelled this process and demonstrated experimentally the feasibility of synchronizing a multiple stage pulsed induction accelerator.

Micromagnetic analysis of magnetic after-effects in amorphous alloys by two-level systems

Abstract: In amorphous ferromagnetic alloys relaxation effects influence all properties of the hysteresis loop. We have investigated with an AC technique (field amplitude \mu_{o}\hat{H} \leq 0.25 \mu T) the magnetic after-effect (MAE) of a nearly non magnetostrictive Co-alloy as well as of magnetostrictive Fe-alloys. On the assumption of thermally activated processes with Arrhenius equations \tau = \tau_{o}.\exp[Q/kT] , for the relaxation times τ, the time and temperature dependence of the MAE can be described by a spectrum of relaxation times. By means of a computer analysis the distribution functions, P(Q), of the activation energies were determined.