Showing papers on "Magnetic domain published in 1989"

Three-dimensional micromagnetic modelling of ferromagnetic domain structure

Abstract: The fidelity of magnetic recording materials (whether they be synthetic crystals on a recording tape, or natural crystals in rocks recording changes in the Earth's magnetic field) depends on the uniformity of their magnetic structure. Such structure is determined by minimizing the energies arising from atomic magnetic dipole interactions. Previous micromagnetic models of coupled spin structures have contained well defined constraints to make the calculations tractable. By using a supercomputer, we have been able to perform unconstrained calculations of minimum energy structures for cubic assemblies of up to 22×22×22 exchange-coupled spins. The critical size for transformation from a uniform single-domain structure to a non-uniform three-dimensional structure is about 0.1 µm for magnetite, as found previously from one-dimensional modelling. However, a variety of different non-uniform structures are possible, with energies and magnetic moments much less than those of conventional lamellar domains. The predicted moments of unweighted combinations of these states agree well with experimental measurements on magnetite in the size range 0.08-0.5 μm. Surface spin structures are such as to minimize flux leakage out of the particle and might be misleadingly imaged by the Bitter colloid technique as indicating a single-domain state.

Magnetic force microscopy of thin Permalloy films

Abstract: We have imaged naturally occurring domains in soft magnetic films using the force microscope. Classic closure structures were seen in both sputtered and plated Permalloy films. These structures were compared to optical Kerr micrographs of the same films, with generally good correspondence. The force microscope had sufficient sensitivity and resolution to observe magnetic details such as ripple structure and a Bloch line. Clear evidence of tip‐induced wall motion was seen when the tip‐to‐sample separation was less than about 100 nm.

Influence of the surface on magnetic domain-wall microstructure.

Abstract: The magnetization orientations in domain walls at the surfaces of an Fe crystal, a ferromagnetic glass, and a Permalloy film, measured by scanning electron microscopy with polarization analysis, exhibit asymmetric surface N\'eel wall profiles which (1) are at least twice as wide as interior Bloch walls in bulk and (2) are described quantitatively by our micromagnetic calculations without assuming any special surface parameters. Misinterpretation of domain-wall widths, Bitter patterns, and magnetic-force-microscopy images can result from overlooking the extreme effect of the surface on magnetic microstructure.

Consequences of Time Reversal Symmetry Violation in Models of High $T(c$) Superconductors

Abstract: We consider some observable consequences of the possible breaking of the discrete space-time symmetries $P$ and $T$ in high-${T}_{c}$ superconducting materials, as occurs in anyon models. It is argued, within these models, that at least two species of anyons are expected to occur, as a result of a quasimagnetic modification of the algebra of translations. We find that there is an intrinsic orbital magnetic moment perpendicular to each anyon layer, whose sign depends on the sign of the broken symmetry in the layer. If the coupling between layers is ferromagnetic, there should be a number of observable bulk effects, including optical rotation and anomalous transport properties analogous to a Hall conductance, which would occur even in the absence of an external magnetic field. Depending on the sample geometry, there may be a magnetic domain structure and/or fringing magnetic fields, and there may be a difference in the value of ${H}_{\mathrm{c}1}$ for positive and negative magnetic fields. If the coupling between planes is antiferromagnetic, so that the sign of the broken $P$ and $T$ symmetry alternates between planes, the bulk effects are absent, but the broken symmetry may be detected in principle by surface-sensitive probes or by weak effects in neutron scattering. Measurements of muon spin relaxation provide a local probe that should be a sensitive detector of broken $P$ and $T$ symmetry in either the ferromagnetic or antiferromagnetic case. For the model of dilute, weakly interacting anyons, we show that the magnitude of the intrinsic orbital magnetic moment can be obtained exactly by a direct physical argument. Our analysis determines all of the coefficients in the effective London Lagrangian, including the Chern-Simons-type terms, if the value of the compressibility is known.

Low-field magnetic response of complex superconductors.

Abstract: Solutions of the Ginzburg-Landau equations for a complex superconducting phase are presented for regions close to a domain wall and to the surface. The finite local magnetization found at these inhomogeneities yields a small magnetic response via a movement of domain walls in an external magnetic field. We examine line defects in the walls which are vortices enclosing a fraction of the universal flux quantum.

Media for erasable magnetooptic recording

Abstract: Amorphous rare-earth-transition-metal alloys are considered as materials for magnetooptic information storage. They can be prepared by evaporation or sputtering on glass or polymer substrates. The alloys are ferrimagnets and exhibit a uniaxial magnetic anisotropy. The magnetic and magnetooptic properties can be well tailored by the composition as well as the deposition conditions. The information is stored by memory magnetic domains which can be written by a thermomagnetic switching process. The reading process utilizes the magnetooptic Kerr effect. In both cases the temperature profile of the saturation magnetization, the uniaxial anisotropy, and in particular the coercivity are of primary importance. At present, the most prominent candidates for device applications are GdTb-FeCo and Tb-FeCo alloys. Carrier-to-noise values up to 61 dB (30 kHz) have been achieved using magnetooptic disks. >

An analysis of perpendicular magnetic recording using a newly developed 2D-FEM combined with a medium magnetization model

Abstract: In order to analyze perpendicular magnetic recording mechanisms, the authors have developed a 2-D FEM (finite-element method) simulation program in which a vectorial magnetization of magnetic particles is introduced into the calculation of magnetization distributions in a recording media. This program makes a physically accurate simulation of magnetic recording and reproducing processes because not only the magnetic nonlinearity of head and medium but also the head-to-medium magnetic interaction are taken into account. It is confirmed quantitatively by the program that stronger head-to-medium magnetic interaction produces a sharper magnetization transition and a higher reproduced voltage at higher recording densities. >

Thin film magnetic head

Abstract: PURPOSE:To prevent the movement of magnetic domain walls and to obtain a thin film magnetic head, which has a stable output, by obtaining >=one non-magnetic part in an island shape in the middle of a magnetic thin film pattern to constitute a magnetic circuit. CONSTITUTION:A magnetic core 1 is composed of the upper and lower layers of the magnetic thin film patterns to be interposed between a coil 2 and these patterns are connected by a back gap part 3 and further exposed to an external part in a slider floating surface 4. In a gap part 5, the patterns are faced each other with a non- magnetic film to be formed by the alumina film, etc., whose thickness is 0.1-1.0mum around, between. For the magnetic core 1, in order to prevent the lowering of magnetic efficiency in the middle of a way from the gap part 5 toward the back gap part 3, patterning is executed so that the width of the magnetic core can be wide from a place to be separated from the gap part 5 by 10-20mum. Further, in the place where the magnetic core 1 is extended, an island-shaped part 6 of non-magnetism, whose length and width are 2-6mum around, is formed and this island-shaped part 6 is formed simultaneously with the patterning of the magnetic core 1. This non-magnetic island- shaped part 6 prevents the large movement of the magnetic domain walls at the time of head operation and presents the thin film magnetic head to have the stable output.

Magnetic microstructure of the (0001) surface of hcp cobalt

Abstract: The magnetic domain structure of the (0001) surface of a hcp cobalt crystal was investigated using scanning electron microscopy with polarization analysis (SEMPA). This is the first observation by SEMPA of both out‐of‐plane and in‐plane magnetization components. The perpendicular magnetization imaged with SEMPA showed a branched structure very similar to that previously observed by magneto‐optic Kerr microscopy. In addition, a previously unobserved in‐plane magnetic substructure was measured. The in‐plane magnetization is divided into well‐defined submicron domains that appear to reflect the sixfold symmetry of the crystal surface.

Magneto-strictive torque sensor

Abstract: A magneto-strictive torque sensor for electrically contactlessly detecting a torque applied to a rotary shaft on the basis of a resulting change in the magnetic permeability of the surface of the shaft. Fine dents and retainer areas for retaining residual compressive stress due to the fine dents are formed on the surface of the rotary shaft. According to this arrangement, the process of magnetization resulting from the application of an exciting magnetic field and of the torque to the rotary shaft involves less magnetization due to magnetic domain wall displacement and consists principally of reversible magnetic rotation, with the result of reduced hysteresis in the magnetization process. The reduced hysteresis causes less hysteresis involved in torque detection and higher detection sensitivity, thus rusulting in high accuracy of torque detection. Further, by working the surface of the rotary shaft for the purpose of forming the fine dents thereon, microdefects present on the surface layer of the rotary shaft are reduced or eliminated and thus reduced hysteresis and improved sensitivity can be attained in the process of torque detection.

Thin‐film magnetic patterns in an external field

Abstract: The behavior of ideally soft ferromagnetic films in the presence of a weak coplanar magnetic field is explored by the method of characteristics. Solutions are found which have no internal field or in some cases have field‐free zones. Results are specifically given for circular and elliptic disks, the infinite strip, and the semi‐infinite plane. The disk solutions have internal domain walls.

Neutron Depolarization in Submicron Ferromagnetic Materials

Abstract: The neutron depolarization technique is based on the loss of polarization of a polarized neutron beam after transmission through ferromagnetic substances. This loss, caused by Larmor precession in individual domains, determines the mean domain size, the mean square direction cosines of the domains and the mean magnetization. The method is complementary to the neutron scattering technique with respect to the size of the inhomogeneities to be determined and the dynamic range accessible. Only the static applications of the method in studying domain structures are considered. As examples will be treated metal foils under stress, oriented ferroxdur permanent magnets, soft ferrites, recording tapes and thin films. In most of these examples magnetic correlations between neighbouring domains are subject of study.

Magnetic properties of the diluted magnetic semiconductor Zn1-xFexSe.

Abstract: The magnetic specific heat and low-field ac susceptibility of the iron-based diluted magnetic semiconductor (DMS) Zn1-xFexSe in the temperature range 0.4–20 K are reported. Antiferromagnetic d-d interactions and indications of spin-glass freezing are observed. These data, together with high-temperature susceptibility and high-field magnetization, are interpreted in the extended nearest-neighbor pair approximation, with an antiferromagnetic exchange between the Fe2+ ions. Fair agreement between theory and experiment is obtained for all the thermodynamic quantities with one set of parameters provided by independent experiments. The strength and range of the interactions, as well as the freezing mechanisms, are compared with DMS’s containing Mn2+, and the results are discussed in relation with the existing models.

Thin film memory device having superconductor keeper for eliminating magnetic domain creep

Abstract: A thin film magnetic array memory affords relatively high packing densities while avoiding the problem of magnetic domain creep through the use of thin films of superconducting material disposed on the work lines of the memory. The superconducting films shunt magnetic fields generated by currents carried within the word lines and prevent these fields from adversely affecting adjacent memory cells in the array. By constraining the magnetic fields with the use of the superconducting films, the word lines can be packed close to one another in the array structure, thereby increasing the amount of information that can be stored in a unit area of the array.

Thermo-magnetic recording method

Abstract: The present invention adopts as the basic s.tructure of its thermomagnetic recording medium an arrangement consisting of a first (11) and a second magnetic thin film (12) having perpendicular anisotropy and a third magnetic thin film (13) having in-plane magnetic anisotropy or small perpendicular magnetic anisotropy interposed therebetween, formed into a laminated structure by being magnetically coupled to the adjoining films in turn, modulates and switches, in accordance with information to be recorded, a first heating condition and a second heating condition, with the medium applied with a predetermined external magnetic field Hex in the direction perpendicular to the plane of the film, the first condition being that for raising temperature of the medium to a first temperature T₁ which is virtually above the Curie temperature TC1 of the first magnetic thin film and not causing reversal of the magnetic moment in the second magnetic thin film and the second condition being that for raising temperature of the same to a second temperature T₂ which is virtually above the Curie temperature TC1 and sufficient to cause reversal of the magnetic moment in the second magnetic thin film, to thereby form an information bit (magnetic domains) in the first magnetic thin film, and adapts during the course the medium is cooled from the heated states such that two states established by the different relationships between the directions of magnetization of the first and second magnetic thin films are finally formed whereby the recording of the information is performed, and thus the present invention brings about conditions enabling alteration of recorded information to other information, that is, enabling so-called overwriting. Especially, by virtue of the third magnetic thin film, the present invention achieves simplification of the apparatus for applying the magnetic field.

Magnetoresistive head and head setting method

Abstract: A method of establishing a single domain in a magnetoresistive sensor positioned in a gap between two shield layers of magnetic material. The method includes the steps of heating the magnetoresistive head above the Neel temperature of at least one of the shield layers of magnetic material. Applying an external magnetic field to the magnetoresistive sensor and the shield layers for establishing a single magnetic domain in the magnetoresistive sensor. Reducing the intensity of the external magnetic field for holding the magnetization of the magnetoresistive sensor during cooling. Cooling the magnetoresistive head.

Magnetic and mechanical properties of amorphous alloys by pulse high current

Abstract: A heating process of improving the magnetic and mechanical properties of ferromagnetic amorphous alloys wherein the amorphous ribbon is treated with rapid heating and rapid magnetic domain impacting in a direct heating manner by means of pulsed high current to improve the magnetism of ferromagnetic amorphous alloys with reduced or eliminated the annealing embrittlement thereof. The heating process is performed in the following conditions: pulse current density: J≧10 3 A/cm 2 pulse duration: tp=1 ns-100 ms frequency: f=1 Hz-1,000 Hz heating time: tn=1 sec.-100 secs.

Computation of fields and forces in magnetic force microscopy

Abstract: In magnetic force microscopy (MFM), a sharp magnetic needle interacts with the field pattern established by the sample near its surface. A cantilever then converts the force on the needle to a displacement, which is measured interferometrically or otherwise. The author describes a model for the tip that takes full account of the micromagnetic interactions involved. The stray magnetic field for a thin film is computed, and the micromagnetic model of the needle is developed. An example calculation is given to illustrate the application of the model. >

Recording experiments on rare-earth transition-metal thin films are studied with Lorentz microscopy

Abstract: Domains written thermomagnetically under recording conditions in rare-earth transition-metal thin films are studied with Lorentz microscopy. A novel technique in which the magnetooptical layer is deposited on specially prepared silicon wafer disks provided with Si/sub 3/N/sub 4/ windows is described. This technique allows direct observation of the written domain patterns in the electron microscope. It is demonstrated that the nucleation process plays a crucial role when writing in TbFeCo. Different compositions having different temperature dependences of the magnetic properties lead to markedly different domain-formation behavior. With the detailed insight into the shape and structure of domains obtained by Lorentz microscopy, carrier and noise levels obtained from recording experiments can be understood. This is demonstrated with data on GdTbFe. It is shown that magnetic-field modulation, apart from the advantage of direct overwrite, offers the possibility of very-high-density recording. >

Bar magnet for construction of a magnetic roller core

Abstract: An improved bar magnet and method of construction, and an improved magnetic core comprising an assembly of such magnets, for use in a processing station of an electrostatographic printing machine. The improved bar magnet is formed of permanent magnet material having magnetic domains therein that are magnetized along epicycloidal curve segments. The external magnetic flux density is improved over that of a conventionally-magnetized magnet. An injection mold for inducing the particular epicycloidal alignment of magnetic domains in the improved bar magnet is provided.

Dynamic switching process of sandwich-structured MR elements

Abstract: The dynamic behavior of sandwich-structured magnetoresistive (MR) memory elements is studied analytically by solving Gilbert's equation together with the one-dimensional micromagnetic torque equation The typical element is 2 mu m*20 mu m and consists of two 150-AA thick magnetic layers separated by a 50-AA thick nonmagnetic layer The easy axis is along the short dimension of the element The theoretical study shows that wall nucleation is present when the switching is driven by a field applied in the easy-axis direction, whereas switching by a field in the hard-axis direction is accomplished by coherent rotation The switching speed predicted by this one-dimensional model is in the nanosecond range and increases linearly with the external fields >

Magneto-resistance, stress effects, and a self-similar expansion model for the magnetization processes in amprphous wires

Abstract: The outer shell magnetization process was investigated from the point of view of its effects on longitudinal and transverse magnetoresistance (MR), magnetization, and domain structure observations as well as their stress effects for a Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous wire with a diameter of 125 mu m prepared by rapid quenching in rotating water. The unusual behavior of the initial negative slope observed in the longitudinal MR is explained in terms of a realistic domain structure. A self-similar expansion model is proposed to explain the dynamical response of such a structure under applied fields and/or tensile stresses. It is suggested that the zig-zag domains of the outer shell are stabilized by a square closure domain which expands uniformly while maintaining a self-similar shape up to a threshold field of about 20 Oe and then deforms towards the saturation magnetization. However, this domain structure was destroyed or much deformed by a tensile stress along the wire axis of about 170 MPa in the sample. Such a critical stress depends on the diameter, quenching conditions, alloy composition, etc. This behavior and stabilization of the zig-zag domain by the closure domains give a novel mechanism for the magnetization processes which follow the re-entrant reversal, and are thus useful for the understanding of re-entrant reversal phenomena themselves. >

Reversal behaviour in perpendicular iron particle arrays (alumite media)

Abstract: Alumite was chosen as an ideal material for investigating the influence of particle interaction on the magnetic behavior of a perpendicular anisotropic particle array. It was found that the measured reduced coercivity versus the reduced diameter curves fit the theoretical curling mode. However, the magnetic behavior will no longer obey curling if the applied field deviates from the film normal. This is due to the presence of magnetic charge next to iron single-domain cylinders, which completely destroys the validity of curling. Their reversal can be interpreted as due to the superposition of Cos-type incoherent rotation and the magnetization reversal caused by the demagnetizing field and the dipole-dipole field. >