Showing papers on "Single domain published in 1971"

Determination of initial magnetization curve from crystallites size and effective anisotropy field

Abstract: It is shown that in YIG the magnetization in low fields is due to the same mechanisms for the whole temperature range to the Curie point. At a given temperature the magnetization curves for different samples can be reduced to a single curve by taking into account the grain size. The interpretation is based on a model proposed earlier by Globus: the value of the reversible magnetization would be determined by the wall bulging, the value of the nonreversible magnetization by the wall displacement inside a spherical grain. For different temperatures a single reduced line is obtained by introducing the saturation magnetization and the effective anisotropy field, which is calculated from the susceptibility measured on a sample with single domain grains. So, it is possible to obtain a single magnetization curve which characterizes the composition.

Calculation of intrinsic coercivity of magnetic domain walls in perfect crystals

Abstract: The critical field strength at which a classical domain wall moves through a perfect ferromagnetic crystal of simplified structure is calculated as a function of the ratio between anisotropy energy K and ferromagnetic coupling energy C , taking into account the discrete nature of the spins. When K approaches C intrinsic wall pinning becomes appreciable with critical fields approaching the anisotropy field when K \gg C . For K/C \geq 2/3 , the wall has a thickness of one atomic distance and thus resembles a ferroelectric wall.

Device implications of the theory of cylindrical magnetic domains

Abstract: This paper applies the theory of cylindrical magnetic domains1 to cylindrical domain devices. The stability conditions are examined as bounds to the region of possible device operation and it is found that the plate thickness, h = 4l, and the domain diameter, d = 8l, where l is the ratio of the wall energy per unit area to 4π times the saturation magnetization squared, are preferred values. When the effects of wall coercivity and mobility are examined, it is found that the preferred plate thickness and domain diameter are even more strongly preferred, that the wall motion coercivity should be less than one percent of 4π times the saturation magnetization, and that a domain coercivity and mobility may be defined. Consideration of the Neel temperature and the desired absolute domain size in addition to the static stability conditions shows that domain materials having some antiferromagnetic character and induced uniaxial anisotropy are preferred. Where appropriate, domain methods for measuring material parameters are described.

Evidence of Single-Domain Magnetite in the Michikamau Anorthosite

Abstract: The Michikamau anorthosite possesses very stable natural remanent magnetization, some of which resists alternating fields up to 1800 Oe. The rock contains two types of opaque grains, fine opaque needles of order 10 × 0.5 μ in the plagioclase felspar, and large equidimensional magnetite particles. Ore microscope studies suggest, but do not establish, that the needles are composed of magnetite. Saturation isothermal remanence and thermal demagnetization studies indicate magnetite as the carrier of remanent magnetization. In order to distinguish the effects of the large grains from those of the needles, mineral separation was used to show that an artificial specimen of essentially pure plagioclase had very similar isothermal remanent magnetization properties to the whole rock. Both indicated magnetite as the magnetic mineral. Thermoremanent properties of the separated mineral fractions indicated magnetite as the dominant magnetic constituent but showed some evidence of laboratory-produced hematite. Theoretic...

Role of Interactions in Magnetic Tapes

Abstract: Thermodynamic and kinetic considerations applied to an assembly of single domain particles have resulted in a single set of equations that describe such diverse processes as hysteresis, time effects, thermoremanent magnetization, and anhysteretic magnetization. An important feature of this work is the inclusion of particle interactions in a consistent manner through the thermodynamic and kinetic formalism. The mechanism of magnetic processes is attributed completely to the thermal activation of moment reversal and not to interactions. Interactions, however, substantially modify the magnitude of the effects.

Magnetomechanical effects in the Rayleigh region

Abstract: A brief resume of basic magnetism is followed by a consideration of the magnetization process in the absence of applied mechanical stress, in which the importance of internal stresses and inclusions is emphasized and which leads to the introduction of Neel's disperse field theory. The Rayleigh laws are interpreted in terms of "Preisach loops." Early work on the influence of stress on the magnetization process is discussed, leading on to a detailed consideration of this phenomenon in terms of three mechanisms which, for simplicity, are taken to be essentially distinct. These are, first, the alteration of the pressure on 90° domain walls by the application of stress; second, the alteration in the opposition term, which must clearly be in balance with this pressure for domain-wall equilibrium, and, finally, large-scale alterations in the overall domain structure. Existing experimental observations, on both magnetically soft and hard materials, are interpreted in terms of these three mechanisms.

Magnetostrictive phenomena in metallic materials and some of their device applications

Abstract: The phenomenon of magnetostriction, or the change in a body's dimensions during the magnetization process, was first reported by Joule. Since then, the interaction between strain and the magnetization process has been studied extensively, particularly in the magnetic metals and alloys that have been found to be of technological importance. The purpose of this paper is to review magnetostrictive phenomena in metallic materials and to discuss a number of devices making use of magnetostriction. After presenting some fundamentals of magnetostriction, a review is given of magnetoelastic effects and magnetoelastically induced anisotropies in magnetic films. Some of the domain patterns and domain visualization techniques that have been found to be related to the magnetostrictive properties of magnetic materials are discussed. The application of magnetostrictive materials to memory devices is reviewed. Included are such areas as magnetostrictive delay lines, ferroacoustic memories of both the flat film and wire type, thermo-strictive recording, and fiat film displays and display memories.

Micromagnetic characteristics of transverse diffuse domain boundaries in permalloy thin films

Abstract: Transverse domain boundaries propagating in the longitudinal direction at speeds one to three orders of magnitude faster than normal domain walls are responsible for most of the lower speed reversals in magnetic thin films. Using a 10-ns exposure time Kerr magnetooptic camera, these boundaries have been photographed for a variety of applied fields in several films with thicknesses ranging from 500 to 3500 A. High-magnification photographs of the boundary transition region reveal that the boundaries consist of small isolated areas of reversed and partially reversed magnetization in a nonreversed background. Propagation occurs by the nucleation of additional small areas of reverse magnetization within and ahead of the transition region. In a given film the width of the transition region increases as the applied field is increased. By approximating the divergence of the magnetization at the boundary as a line charge, a model has been derived which predicts the boundary width W to be W = \frac{8M_{s}t}{H_{n}}\frac{1}{(1-H/H_{n})} where M s is the saturation magnetization and H is the applied field. The nucleation threshold H n is the threshold at which nucleation is observed over all the film. The experimental data fit this predicted dependence quite well. The rapid increase in width of the transition region with applied field is correlated with a rapid nonlinear increase in the velocity of propagation.

Wall Stability of Cylindrical (Bubble) Domains in Thin Films and Platelets

Abstract: The stability in an applied magnetic field of a domain of reversed magnetization in an otherwise uniformly magnetized thin‐film medium, has been investigated experimentally and theoretically. From a free energy point of view, a field applied antiparallel to the magnetization of the reversed domain tends to affect the size of the domain based on energy minimization. Assuming a cylindrical domain, we have: (1) calculated the total energy due to the domain wall, the magnetostatic field, and the applied field; (2) compared the inward force on the domain wall derived from this total energy with a coercivity or retarding force to establish a threshold applied field for domain motion; and (3) compared theoretical predictions with experimental results in both MnBi films and an orthoferrite platelet. Comparisons were based on values of saturation magnetization and domain‐wall energy density which are believed typical or have been reported elsewhere. Agreement of the data with calculation is considered satisfactory for both media. The requirement of accurately measuring MnBi spots of the order of 1 μ in size was met using an automatic Faraday modulation polarimeter. A detailed description of this novel instrument is included.

Domain structures in magnetic materials with high crystalline anisotropy

Abstract: Some of the factors which affect domain structures in magnetic materials with high magnetocrystalline anisotropy include crystal perfection, nonmagnetic or weakly magnetic inclusions, and the nature of grain boundaries. In whisker-like barium ferrite crystals about 3 μm in thickness straight (180°) domain walls were observed in the basal plane. Reverse domains did not nucleate at fields of over -5000 Oe after first saturating the crystals in a positive magnetic field. In less perfect crystal platelets of about the same thickness the domain structures form in what may be described as a convoluted pattern, and after saturating in a positive magnetic field, reverse domains nucleate in positive fields of from +100 to +1000 Oe. An analysis of the convoluted patterns has shown disclination structures of several types. The influence of internal defects as well as the effect of surfaces, nonmagnetic inclusions, and grain boundaries on domain structures in magnetic materials with high crystalline anisotropy are described and discussed.

Demagnetizing fields in bubble-domain investigations

Abstract: A theory of cylindrical domains is presented for cases of a single domain in a plate of finite extent and of many domains scattered at random in a plate of infinite extent in the plane. Force and stability functions are determined for both cases. New unexpected solutions showing stability without a bias field, as well as those, for which the bias field must be directed in compliance with the magnetization in the cylindrical domain, are obtained. It is proved that the neglect of finite plate dimensions, as well as of the interaction between domains, is the cause of the apparent dependence of energy density of the domain wall on the bias field as stated in other reports. Theoretical considerations are proved by the experiments on the domain structure carried out on YFeO 3 orthoferrite.

Proton Magnetic Resonance in Antiferromagnetic Ni(NH3)2Ni(CN)4·2C6H6

Abstract: The magnetic spin structure of the antiferromagnetic Ni(NH 3 ) 2 ·Ni(CN) 4 2C 6 H 6 has been investigated by means of proton nuclear magnetic resonance measurements. From the angular dependence of resonance lines in an external field, an ordered magnetic structure (unit cell dimension, a * = a , b * =2 a and c * =2 c ) is inferred in which ferromagnetic chains parallel to a -axis, are arrayed antiferromagnetically to adjacent chains. The magnitude of internal fields at proton sites could be explained by single domain model. But the rotating diagram of the resonance patterns in the c -plane shows that the substance has antiferromagnetic domains.

Mössbauer studies of the relaxation behaviour of β Co fine particles

Abstract: The Mossbauer effect in Fe5 7 has been used to study the relaxation associated with the transition from ferromagnetism to superparamagnetism in β Co fine particles. By observing Mossbauer absorption spectra as a function of particle size, the critical volumes for single domain particles have been estimated at 8 K, 83 K and 300 K. In this way the relaxation time may be related to particular values of the energy barrier between stable magnetic states (measured in units of kT) and the results compared with theoretical predictions.

Magnetic Domain Structures of High Permeability Alloys

Abstract: The magnetic domain wall images in permalloy and 5% Mo-permalloy with high magnetic permeabilities were observed by means of Lorentz microscopy. The specimens were of the form of thin films prepared by electrolysis of bulk materials. Correlating these observations with the initial permeabilities, it was found that, as the initial permeabilities become high, the magnetic domain walls change their appearances from straight lines to curved lines and finally they vanish in part. In a local part about 20µ in diameter of the specimen with permeability at 0.001 Oe, µ 0.001 =120,000, typical circularly magnetized domain pattern has been observed for the first time in a monograin state. The energy calculation for this configulation with circular magnetization was performed. Comparing this result with that for a uniformly magnetized domain, the existence of the circularly closed magnetic domain in low effective anisotropy–high permeability–magnetic materials is justified.

Magnetic properties of assemblies of single domain elliptical platelets

Abstract: Magnetization and remanence loops for a uniform spatial distribution of noninteracting single domain thin discs of elliptical shape are calculated It is found that the relative remanence of such a system has magnitude 0638 The temperature dependence of hc and hR is investigated and found to be approximately linear over a temperature range depending upon the particle volumes and anisotropy The values of hc and hR are found to be 0562 and 0648 at T=0K, respectively The results are compared with those obtained for a uniform distribution of uniaxial particles

The domain structure and magnetizing curves of thin single-crystal iron platelets

Abstract: The dependence of the magnetic domain structure of perfect crystals of pure iron in the shape of platelets on the external field is studied using the colloid technique. The magnetizing curves are determined from the domain configuration. It is found that their shape is determined by the demagnetizing effect of the platelets. The demagnetizing charges are distributed on the domain walls within the volume of the sample so that the domain configuration influences the demagnetizing factor. By measuring the demagnetizing factor we can determine the thickness of platelets.

Magnetic field detection using coherent magnetization rotation in a thin magnetic film

Abstract: Magnetic field detection by magnetometer with coherent magnetization rotation in thin magnetic film

Magnetiostatic interactions in some bubble-domain propagation circuits

Abstract: Cylindrical magnetic domain (CMD) propagation actually comes to the generation of magnetostatic traps (MST) which successively "capture" the domains on their way along the propagation path. There are three types of MST which correspond to three types of magnetostatic interactions between a domain magnetization and "active" elements of propagation circuits. An interaction of CMD magnetization with ferromagnetic overlay (the third type of an interaction) can generate MST with the maximum depth of approximately 16 Oe. NIST depth in practical propagation circuits is bound to be 6-10 Oe. The data rate upper limit for the techniques using the interaction of CMD and ferromagnetic overlay is determined by the minimum time interval necessary for domain capture by MST and for orthoferrites, which is approximately 1 Mbit/s. The rare-earth orthoferrite single crystals synthesized by the floating zone technique were used throughout the experiments.

A method for measuring the temperature dependence of the magnetization in uniaxial garnets

Abstract: A method for measuring the temperature dependence of the saturation magnetization for uniaxial magnetic garnets is described. The advantage of the method is that it uses an isolated bubble domain without the need to destroy the bubble in order to obtain the measurements.

Control of Domain Propagation in Magnetic Thin Films

Abstract: Magnetic domain propagation behavior in narrow channels composed of a Permalloy thin film imbedded in a high coercive film is discussed in this paper. The domain propagation is affected by channel shape and by magnetic potential barriers in the channel. The domain‐wall velocity along the channel can be controlled by the demagnetizing field in the channel. The domain grows along the channel under applied pulse fields. To obtain a stepwise movement of domain wall under pulse fields, periodic barriers of magnetic potential comprising high coercive force film were introduced. When the demagnetizing field in the channel is larger than 1/3 of the intrinsic coercive force of the channel material, an oval domain nucleates and shifts along the channel under successive applied field pulses. Reversed domains are observed using the Kerr magneto‐optic effect.

Critical Switching Curve and Hysteresis Loop Due to Fanning Spin Structure in a Thin Magnetic Film

Abstract: New critical curves and hysteresis loops for a single layer magnetic thin film are calculated on a rectangular coordinate (Hx, Hi). Hi is the inhomogeneous internal field caused by the current passed through the film and Hx is the field parallel to the easy direction of magnetization. In this case direction of the spins varies within the film plane, and the single domain model cannot be used. The film is divided into multi-layers and the spin distribution is solved numerically using the variational method. It is shown that there exists a region where the fan-shaped spin configuration like the Bloch wall twists by more than 180 degree, and also that the critical switching curves change severely with the film thichness.

Approach to saturation in inhomogeneous magnetic materials

Abstract: The Neel theory of the approach to saturation in inhomogeneous magnetic materials is critically reviewed. It is found that the theory is rigorously applicable when the local saturation magnetization differs only slightly from its spatial average, but that this condition is not satisfied in porous materials or in material containing inclusions of a second magnetic phase having a saturation magnetization twice that of the host material or larger. The Neel theory is extended by (i) calculating the high‐field behavior of the magnetization curve for arbitrary inhomogeneity, and (ii) calculating the magnetization curve for arbitrary field strength to a higher order of approximation than in Neel's theory. The results show that for porous materials, as well as for materials containing a second magnetic phase, the higher‐order corrections are quite significant. The higher‐order corrections to the Neel theory are found to depend quite strongly on the shape of the inclusions, being smallest for spherical inclusions and approximately six times larger for layerlike inclusions.

Elastic tension effect on magnetic properties of ferromagnetic films

Abstract: The present work describes the results achieved in investigating the influence of mechanical stresses on the processes of quasi-static magnetization reversal, the dynamic characteristics and the creep of the domain walls of Fe-Ni films with Ni content from 60% to 90% and the thickness from 150 A to 3000 A.