Magnetization Reversal Model Research Articles

長手磁気記録における回転磁化モードの形成過程 計算機シミュレーションによる解析

The longitudinal magnetic recording process has been simulated by a super computer and compared with that of perpendicular magnetic recording. A curling incoherent magnetization reversal model and the statistical calculation of probable magnetization for magnetic particles in the interior of the magnetic layer of a medium have been introduced to the computer simulation. It has been theoretically confirmed by the computer simulation that the circular magnetization mode is formed in the medium at high desity recording and causes the recording demagnetizing loss, as we predicted qualitatively about twenty years ago.

計算機シミュレーションのための垂直磁気記録媒体磁化モデル

In order to compute the vectorial magnetization process of a crystalline particle in a Co-Cr sputtered film, a magnetization reversal model was investigated. A curling mode and a statistical method were introduced for the calculation of a probable vectorial magnetization of the particle. Using this method, the M-H loops of Co-Cr films were restored well by computer. Simulation of the perpendicular magnetic recording process was carried out in good agreement with the measured reproduced waveforms.

Magnetization models of Co-Cr film for the computer simulation of perpendicular magnetic recording process

The microscopic magnetization model of medium and the statistical calculation of the vectorial magnetization are proposed in order to give a reliable computer simulation of magnetic recording process. The curling incoherent magnetization reversal mode is introduced for the magnetization model of crystalline particles, because the coherent magnetization reversal model is insufficent for the restoration of M-H loop of Co-Cr film having lower coercive force than the anisotropy field strength. Using the newly proposed method, the vectorial M-H loops of Co-Cr film can be restored well by computer. It will be very useful for the computer simulation of perpendicular magnetic recording.

Magneto-optical measurements of hysteresis loop and anisotropy energy constants on amorphous TbxFe1−x alloys

Measurements of the Kerr magneto-optic effect, coercivity, and anisotropy energy constants are performed in a magneto-optical system that combines the Kerr rotation angle and ellipticity to enhance the strength of the signal. The temperature dependence of the polar Kerr effect is compared with the magnetization of the iron subnetwork in the mean-field approximation and good agreement is obtained in all cases. Coercivity is found to be a strong function of the sweeping frequency and the saturating field and the results are found to be in qualitative agreement with the magnetization reversal model based on the existence of initial nuclei in a saturated film and the subsequent growth of these nuclei under a reverse field. Finally, perpendicular magnetic anisotropy energy is studied by magneto-optical techniques and the first two coefficients in the expansion of anisotropy energy in powers of the angle of deviation from the easy axis are determined.

Particle-like magnetic behavior of rf-sputtered CoCr films

This paper summarizes measurements on CoCr films that appear to indicate particle-like behavior of the magnetization reversal. The films studied were rf-diode sputtered onto glass substrates and had a magnetic moment of 400 emu/cm3 (at about 17 at. % Cr content). Particle-like structure of CoCr films has been reported by many authors because of the SEM fracture cross sections which show a columnar microstructure with long thin particles extending through the film thickness. Temperature variations of coercivity and anisotropy fields are found to track approximately indicating that the coercivity is primarily of crystalline origin but also the difference in the slopes of these curves is explained almost exactly by a particle model consistent with the SEM fracture cross sections. Preisach diagrams were constructed from the shear corrected hysteresis loops and found to be extremely narrow. Further, the Preisach data correctly predicts initial magnetization curves. The Preisach diagram results suggest a magnetization reversal model of particles that are magnetically noninteracting except for the sheet demagnetizing fields of the film. Much data exists to support the idea of phase segregation in the CoCr alloy system, again in support of the particle idea. Rotational hysteresis loss measurements were made which indicate magnetization reversal by way of a curling or buckling mechanism, again indicating a particle-like behavior. Coercivity as a function of field angle was measured yielding results consistent with curling or buckling as the primary reversal mechanism. Almost all available data is explained by a model of magnetically isolated particles that interact magnetically only through the film demagnetizing fields and individually reverse by curling or buckling.

Charged wall formation and propagation analysis in ion-implanted contiguous disk bubble devices

Magnetic anisotropy energy along a pattern edge is found to be important for charged wall formation at the pattern edge in ion-implanted contiguous disk bubble propagation track. Charged wall formation and propagation are found to be little affected by the demagnetizing effect at the pattern edge. Charged wall formation and propagation mechanisms are well explained on the basis of the Stoner-Wohlfarth magnetization reversal model, taking into consideration magnetic anisotropy energy along the pattern edge.

Characterization of domain-wall nucleation sites in SmCo5 single crystals

Domain-wall nucleation fields in several single crystals of SmCo5 have been measured. These results, together with a model for magnetization reversal, were used to determine the domain-wall gradients and local demagnetizing factors at specific nucleation sites. Exposing the samples to hydrogen led to a degradation of permanent magnet properties.

Magnetic properties of cobalt rare-earth thin films

This paper describes the magnetic properties of dc sputtered thin films of Co-Gd and Co-Sm in various compositions. Magnetic moment density, hysteresis loop coercivity and squareness, and rotational hysteresis loss measurements are reported. Crystallite and domain sizes were observed with an electron microscope for a few compositions. A tentative model of magnetization reversal is proposed for some of the compositions.

Sea-floor spreading rate changes in the South Atlantic

A computer correlation technique was used to deduce the spreading history of the Mid-Atlantic Ridge from 5 magnetic profiles between 28°S and 43°S. In general, several possible histories are indicated for each profile involving changes of spreading rate and faulting, some of which are easily overlooked by the visual method. The only spreading history that was consistent will all the profiles required spreading at approximately 2.2 cm yr-1 from 11 m.y.b.p. to approximately 5.5 m.y.b.p., followed by a decrease in rate to 1.7 cm yr-1 relative to the Vine (1966) magnetic reversal model based on the South Pacific. Comparison of the data with other reported spreading rate discontinuities suggests that the South Pacific may be reponsible for the reported spreading rate changes.

World-Wide Correlation of Mesozoic Magnetic Anomalies, and Its Implications

In the course of correlating three sets of Mesozoic magnetic lineations in the western Pacific (the Phoenix, Japanese, and Hawaiian lineations), Larson and Chase (1972) determined a paleomagnetic pole for the Pacific plate for the Early Cretaceous. Using this pole we have derived a magnetic reversal model for the Hawaiian lineation set. We then have used this model to correlate the entire Hawaiian lineation set to the entire Keathley lineation set in the western North Atlantic. On the basis of these correlations and drill holes associated with the lineation patterns, we have extended the geomagnetic reversal time scale back to the base of the Late Jurassic (162 m.y. B.P.). A period of reversals occurred corresponding to the Hawaiian and Keathley lineations from 150 o t 110 m.y. B.P., and these reversals are bracketed by long periods of dominantly normal polarity (the Cretaceous and Jurassic magnetic quiet zones). This magnetic reversal time scale significantly alters previous notions of the timing and origin of sea-floor spreading features in the Atlantic Ocean. It implies that the Bay of Biscay opened sometime during the interval between 150 and 110 m.y. B.P.; that drift in the South Atlantic was initiated at sometime during the interval from 110 to 85 m.y. B.P. (probably close to 110 m.y. B.P.); and that the seaward portion of the marginal quiet zones of the eastern United States and northwestern Africa resulted from sea-floor spreading during the Late Jurassic period of dominantly normal magnetic polarity prior to 150 m.y. B.P. In the Pacific during the late Mesozoic, spreading was occurring from at least five spreading centers joined at two triple points. The vast majority of the Pacific Basin today is occupied by only the Pacific-plate side of these spreading patterns. This implies that an area equal to most of the Pacific Basin has been subducted beneath the surrounding continents since the Early Cretaceous. Our magnetic reversal time scale calls for a rapid pulse of spreading from about 110 to 85 m.y. B.P. at all the spreading centers in both the Atlantic and Pacific Oceans. This implies a pulse of rapid subduction around the rim of the Pacific that we relate to episodes of large-scale plutonism in eastern Asia, western Antarctica, New Zealand, the southern Andes, and western North America during the Late Cretaceous.

Late Mesozoic Evolution of the Western Pacific Ocean

A set of east-trending magnetic anomalies located in the western equatorial Pacific Ocean near the Phoenix Islands is Early Cretaceous in age. The use of magnetic reversal model studies shows that this lineated anomaly pattern correlates with one east of Japan that trends east, and with one west of Hawaii that trends northwest. These patterns were formed in their present relative positions, but about 40° (4,500 km) south of their present geographic locations. The configuration of these three contemporaneous sets of magnetic anomalies implies that the Late Mesozoic tectonic pattern consisted of five spreading centers joined at two triple points. In this interpretation, the oldest part of the Pacific Ocean lies just east of the Mariana Trench and is Early Jurassic in age. This Mesozoic system evolved into the Cenozoic spreading pattern recorded in the eastern Pacific Ocean. The details of this transition are open to speculation because it occurred during a period in the Late Cretaceous that lacked magnetic reversals. We propose a model that suggests the northern triple point jumped southeast about 2,000 km at 100 m.y. B.P., and that the Emperor Trough was a transform fault of large offset during the Late Cretaceous. The southern triple point migrated rapidly toward the south-southeast, approximately parallel to the Eltanin Fracture Zone–Louisville Ridge complex that we extend o t the westernmost of the Phoenix lineation fracture zones.

Magnetic properties of Tb-substituted GdIG films chemically deposited on YAG substrates

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.

Alternating and rotational hysteresis losses of γ-Fe<inf>2</inf>O<inf>3</inf>powders in a nonmagnetic matrix

Some aspects of the alternating and rotational hysteresis losses of very diluted samples of γ-Fe 2 O 3 particles are examined. The packing fraction p of the particles ranges from 0.001 to 0.120. The coercive force is found to be independent of p . The alternating and rotational hysteresis losses appear dependent upon p for p ; the rotational losses increase considerably as p approaches zero. The values of the rotational hysteresis integral are close to the theoretical ones corresponding to the model of magnetization reversal of chain of spheres with fanning, but they increase slightly with decreasing p for p . Generally, the ratio of rotational to alternating losses is about twice that for bulk materials. All these effects are ascribed to a weakening of the magnetic interactions among particles.

Magnetization reversal models for a magnetic element, the ?integral comb?

Physical models of magnetization reversal for a polycrystalline ferrite element, a one-piece comb, are considered at the moments of writein and of nondestructive information readout.

Magnetization reversal in films with biaxial anisotropy

Two models of magnetization reversal for the case of films with biaxial anisotropy are considered: 1 ) the coherent rotation model of Stoner and Wohlfarth (S-W) and 2) the noncoherent or wall-motion model of Kondorsky (K). The former has been considered by several authors previously while the latter is developed in the present paper. The (K) model presumes that the anisotropy field is much larger than the critical field for wall motion and that only the component of the applied field perpendicular to the bisector of the initial and final positions of the magnetization is effective. It also presumes that whenever the effective component exceeds a certain critical field determined by the structure of the sample, the magnetization will switch. Rotational hysteresis, torque curves, and hysteresis loops observed on single-crystal cobalt films exhibiting biaxial crystalline anisotropy are compared with the predictions of both models. It is found that at low fields the (K) model is a much better description than (S-W) while at high fields the reverse is true. This behavior is analogous to the behavior of uniaxial polycrystalline films with low values of H_{c}/H_{k} . This similarity and others suggest that the true reversal process is as complicated in single-crystal films as in polycrystalline films, and that dispersion in both the magnitude and direction of the anisotropy is present. Because the samples are single-crystal, single-element films, the possible causes of dispersion are reduced. The most likely cause is locally varying stresses arising from uneven substrate bonding.

Ramp Field Switching in Thin Magnetic Films

AbstractA model of magnetization reversal by the domain wall movement is proposed. This model is formulated in general for polycrystalline square loop ferromagnets which are magnetized by a linearly increasing magnetic field. The switching time and dynamic coercivity of the material are expressed as a function of the rate of increase of the field. These calculation are based on the expression for the velocity of a domain wall obtained from the well‐known Landau‐Lifshits equation. Experimental results, for thin permalloy films are in good agreement with theoretical predictions. A practical aspect of the present work is a new method of determining the static coercivity of the material.

Flux Reversal by Noncoherent Rotation in Magnetic Films

A model of magnetization reversal in thin ferromagnetic films is proposed. The model is based on a small angular dispersion (∼3°) in the film plane of the axis of planar anisotropy. The dynamical effects of this dispersion are important when the switching field (Hs) is of the order of the anisotropy field, fall off rapidly with increasing Hs, and include a two- to threefold increase in the switching coefficient for bias field large enough to insure unidirectional rotation. In addition, it is shown that the transverse flux reaches its maximum before the longitudinal flux is one-half switched. These results are in reasonable agreement with experiment.