Showing papers on "Single domain published in 1977"

An analysis for the magnetization mode for high density magnetic recording

Abstract: By the analysis of the self-consistent magnetization and the direct observation of the remanent magnetization of a real tape, the authors discussed the obstacles which are, and will be, encountered in attaining a higher recording densities with the present magnetic recording system, which uses mainly a longitudinal magnetization mode. Then the properties of the three magnetization modes (longitudinal, circular, and perpendicular) are compared. The mode transformation is also discussed. Finally a new perpendicular magnetic recording system is proposed for high density recording. And some results of fundamental experiments are presented. The system uses the perpendicular magnetization mode which is basically free from the demagnetization in very high densities. Its realization mainly owes to the development of a perpendicular anisotropy film and perpendicular magnetic heads.

Initial magnetization, remanence, and coercivity of the random anisotropy amorphous ferromagnet

Abstract: We analyze the coercivity, remanence, and initial magnetization of a single-domain, single-component amorphous material. We assume a uniform ferromagnetic exchange and concentrate on the effect of single-ion anisotropy. We find a threshold anisotropy below which the coercivity is zero. At large anisotropy, the coercivity is proportional to the anisotropy energy. Exchange pulling increases the remanence of amorphous materials. We suggest that exchange pulling between crystallites may also be operative in small-grain metallic polycrystals.

Hysteresis curves and magnetization processes in a model for an amorphous magnet with random uniaxial anisotropy

Abstract: We consider the magnetic field behavior of a simple model for an amorphous ferromagnet with random single‐ion anisotropy. The spins are taken as classical unit vectors located at sites of a dense random packing model and coupled via nearest‐neighbor exchange interactions. An easy‐axis direction is chosen at random for each site. For large anisotropy, the coercivity is very large and the hysteresis curves resemble those found for amorphous TbFe2 at low temperature. As the anisotropy is reduced, there is a fairly abrupt change in the behavior of the model indicating that sufficiently weak random anisotropy is effectively averaged away. We have examined the energy of metastable states. The results indicate that the canted aligned state is always more stable than low‐moment spin‐glass‐like states. We also consider the magnetization process in the presence of imposed domain walls and find that wall motion is preceeded by magnetization rotation in the high‐coercivity regime.

Domain wall size and magnetic losses in frequency spectra of ferrites and garnets

Abstract: It is shown that the value and the frequency of losses in susceptibility spectra follow the relation established by Globus : the value of μ" is proportional to the mean grain size D m , the relaxation frequency is proportional to 1/D\min{m}\max{2} . Curves obtained from series of NiFe 2 O 4 and YIG samples with various D m are reduced to single curves. It has been also possible, by taking into account the specific properties (the spontaneous magnetization, the total and magnetocrystalline anisotropy fields) to reduce the final single curves for both the compositions to a single intercomposition curve of losses as a function of frequency.

The Demagnetization Field of Multidomain Grains

Abstract: The demagnetization ‘constant’, N, enters into all theoretical considerations of multidomain remanence. Although most workers believe N to be related simply to the shape of the grain, no theoretical study of N has previously been completed. It is shown in this paper thatN monotonically increases with increase in remanence in multidomain grains. Although N can be approximated by a constant in the limit of small displacements of domain walls from their demagnetized sites, this constant critically depends on the domain geometry.

On the Origin of Stable Remanence in Pseudo-Single Domain Grains

Abstract: The existence of pseudo-single domain (PSD) grains was postulated by F.D. Stacey in 1962 but a viable quantitative model for the magnetic moment of the canonical case of a PSD grain (a two domain grain with a single 180° wall) was explicitly derived only in 1974 by F.D. Stacey and S.K. Banerjee. According to this model, the net magnetic moment of a PSD grain arises from the wall moment alone and the high stability to alternating field demagnetization is mainly due to pinning of the wall by large surface anisotropy in such fine grains. Recent theoretical work in micromagnetics shows not only that the canonical case described above is a crude approximation but that the complexities of spin orientations in such grains are far too large so as to allow a theoretical prediction of the expected moments. Much more hope, however, can be gained from recent experimental studies on rare earth-cobalt alloys and yttrium iron garnet crystals. These studies support the basic contention that the role of surface anistropy is indeed the predominant one in explaining the high coercivity of PSD grains. These studies also provide useful experimental models for future research in this area in rock magnetism.

A comparison of rapid surface and volume magnetization measurements on 50% NiFe tape with models of eddy-current-limited domain wall motion

Abstract: Drive field characteristics during rapid (0.1-7 T mu s-1) constant-voltage magnetization reversals in HCR tapes of thickness 6, 12 and 25 mu m are reported. Four stages may be distinguished: (i) a sharp rise of instrumental origin, (ii) a fairly level 'step', (iii) a roughly linear rise that accords well with the 'saturation-wave' (SW) model, and (iv) a steep rise before saturation. Magneto-optic observation shows that the surface magnetization practically saturates at the step to SW transition. This occurs relatively earlier the faster the switch and the thicker the tape. Two models for the step stage are considered. In the first (BDM) bar domains are separated by walls that span the tape thickness. The second (SDM) consists of surface domains of roughly semi-elliptical cross-section. Both assume a detailed balance between domain wall surface tension and magnetic field pressure.

Magnetic properties and magnetic reversal peculiarities of single crystals of R(Co 1-x Ni x ) 5 compounds

Abstract: The basic properties (saturation moments, Curie temperatures, anisotropy constants) and magnetic reversal processes have been studied systematically on the bulk single crystals of quasibinary solid solutions R(Co 1-x Ni x ) 5 , where R = Y, La, Ce, Sm, and Gd. The magnetic reversals have been studied also on the single crystals of similar compounds with R = Nd, Dy, and Er. The general property of all studied systems is a very high coercive force H c connected with domain wall pinning in compounds of quasibinary region. The H c (x) dependenses for all systems are similar qualitatively. There exists a maximum of H c in region x = 0.6 - 0.7 for compounds with trivalent R, and in region x = 0.3 - 0.4 for compounds with tetravalent R. The single exception is the Gd system, where H c has rather low values for all x. The explanation is suggested for H c (x) dependence in which the compositional heterogeneities are considered as the main reason of domain wall pinning in the quasibinary compounds. These heterogeneities are always present as a result of statistical nature of Ni substitutions for Co.

Improvements to a self-consistent model for the magnetic recording properties of non-particulate media

Abstract: Three aspects of self-consistent calculations are considered. The first includes various numerical techniques for reducing by a factor of 60 the running time of the original program. Second, a detailed treatment of the recording characteristics of the thin film head is given. Third, the model is expanded to two dimensions and used to compute with head motion the magnetization vector in a Fe 3 O 4 storage medium of moderate thickness. The role of this usually neglected out-of-plane magnetization component is discussed.

Measurement of Initial Dielectric Constant of KH2PO4 by Thermal Noise Method

Abstract: The dielectric constant of KH 2 PO 4 along the ferroelectric axis is measured at 1 kHz between 90 K and 130 K by a thermal noise method by which one can obtain the dielectric constant without applying Chi external field. The results well agree with the values obtained by the usual bridge method, using the external field of 1 to 20 V/cm, when extrapolation has been made toward zero external field. In the ferroelectric phase, the initial dielectric constants of the multi-domain crystal thus determined are of the order of 10 2 times as large in magnitude as those of the single domain crystal. It is concluded that the most part of the initial dielectric constants of multi-domain KH 2 PO 4 crystal are due to the domain wall motion. A simple model is proposed to give a relation between the domain wall motion and the initial dielectric constant.

Single Domain Oxide Particles as a Source of Thermoremanent Magnetization

Abstract: Single domain (SD) particles have long been suggested as a potentially strong and stable source for the paleomagnetic signal, but their actual occurrence in rocks has been much questioned. Two possible modes of occurrence of SD Fe-Ti oxides can be distinguished. These are as magnetite rods bounded by ilmenite lamellae in intergrown grains (analogous to Alnico permanent magnet alloys), and as isolated ultrafine particles, perhaps representing part of a much broader grain-size distribution (analogous to the oxide coatings used in tape recording). The evidence for the presence in rocks of these two types of magnetic particle is reviewed. Where intergrown grains are present the SD ‘Alnico model’ seems to be valid, and where isolated titanomagnetite grains are involved the SD ‘tape-recorder model’ is satisfactory. Where pure Fe3O4 particles are involved the situation is less clear, and current thinking stresses the role of the so-called pseudo-single domain (PSD) moments.

Single-domain theory for the reversible effect of small uniaxial stress upon the remanent magnetization of rock

Abstract: This paper on small uniaxial stress changing the remanent magnetization of rock is a companion to my previous paper on stress changing susceptibility, both phenomena being of current interest in at...

Cylindrical magnetic domains

Abstract: This review is devoted to a systematic exposition of theoretical and experimental results related to the physics of cylindrical magnetic domains (bubbles). The stability problem is discussed for an individual cylindrical domain and for a lattice of such domains, with allowance for the effect of the coercivity on the stability and dynamics of cylindrical domains. A detailed discussion is given of the laws of motion of cylindrical magnetic domains under the influence of inhomogeneities of magnetic field, temperature, and plate thickness. Phase transitions in a lattice of domains are considered, and the singularities of the magnetization and magnetic susceptibility in such phase transitions are determined. A theory is given for waves propagated in a lattice of domains. Detailed consideration is given to the effect of external factors and of the parameters of the magnetic material on the dynamical properties of a lattice of domains.

The magnetization process in cubic ferromagnetic single crystals

Abstract: On the basis of symmetry arguments the seven possible modes of magnetization of a cubic ferromagnet are enumerated. The case where the magnetic field is in a direction is discussed in detail.

Intrinsic magnetic hardness in SmNi 4 M (M = Fe, Cu, Al)

Abstract: Homogeneous materials SmNi 4 M (M = Fe, Cu, Al) of CaCu 5 type show the phenomenon of strong intrinsic magnetic hardness, that is, magnetic hardness in homogeneous single phase materials independent of particle size. A linear temperature dependence of the coercive forces H c with T1/2is observed.

Magnetic head employing hard axis thin film inductor

Abstract: A flux-sensitive magnetic head employs, at its back part, a structure having a thin single domain magnetic film coated thereon. A coil wraps around the coated structure, and a direct current is passed through the coil, thereby to apply a hard axis magnetic bias to the film. Signal flux appearing at the head front gap asserts a magnetic force along the hard axis of the film. Contrary to what would be expected, the signal flux causes the inductance of the coil to vary. Such inductance variation may be conveniently detected by (1) connecting the variable inductor into a tank circuit, (2) applying a high frequency ac ripple to the "hard axis" dc bias, and (3) measuring the "hard axis" detuning experienced by the tank circuit.

Manufacturing method of single domain single crystal

Abstract: PURPOSE:To simplify the manufacturing process and obtain strong dielectric crystal of high quality which has few defect by domain wall, by producing it in one process of single crystalization and making single domain.

Orientation effects on the magnetization of NbTi superconductors

Abstract: Magnetization measurements in slowly varying fields have shown an anisotropy of pinning forces and of hysteretic losses for different angles α between conductor axis and magnetic field. With decreasing α the hysteretic losses are growing and catastrophic flux jumps appear depending on magnetic history. At intermediate angles alterations in shape of the magnetization curve are observed which may be due to flux lines inclined to the external field. Moreover, in twisted multifilamentary wires fast pulsed longitudinal fields influence the area of the magnetization curve as well as its shape and position.

Magnetic bubble domains in some axially symmetric fields

Abstract: Behaviour of a bubble domain having more than one stable diameter for a single value of the bias field is discussed. Immersing the bubble into specially shaped axially symmetric fields (stray fields of an adjacent magnetic structure) makes it possible in principle to construct memory elements with either destructive or non-destructive reading.

Observation of magnetic domains in MnSb and MnBi single crystals by the kerr effect and a replica method

Abstract: Comparison of Fig. 3a and 4a shows that the patterns for are identical. These results together with our observations parallel to the C-axis suggest that the superficial domain structure in this compound codsists of 180" domains of reverse magnetization The collections of the ferrofluid particles only along the area which penetrate into the crystal as spikes as illustrated by Fig. 5a. where the domain walls terminate at the surface verify that the magnetization within the spike domain is uniformly magnetized normal to the surface across the domain as in the case of barium ferrite or magnet~plumbite.~.~ This type of magnetization provides the high contrast for the patterns observed by polar Kerr effect for the demagnetized crystal. The domain width as determined from Fig. 4a is -1p wide which is about two orders of magnitude smaller than in the bulk of the crystal. For Mn1.,,Sb, the pattern of Fig. 4b obtained by the TEM-replica method revealed a finer structure than that observed by the polar Kerr effect. Comparison of Fig. 3b to 4b shows that the fine dendritic type structure observed by the TEM-replica shown by the polar Kerr effect. The width of the branch of the method exists within the rickrack and the many sided ring patterns dendritic structure is -0.3~ which is more than three times smaller than the domain width of MnBi. If one assumes that the branch represents an antiparallel 'domain of the type shown in Fig. 5a, then a simple calculation of the domain size based on antiparallel magnetization with the experimental values of M, and K fails to account for the large difference in the width of the surface domain for MnBi and Mnl,15Sb. The existence of the dendritic structure patterns in Mn&b indicates that the superficial domains have a

A microscopic analysis of eddy current losses in ferromagnetic conductors

Abstract: The eddy current losses due to domain wall motion in a thin ferromagnetic conductor have been investigated by taking into account the movement of the individual spin vectors within the translating domain wall Both the horizontal and vertical components of the changing magnetization within the wall are considered The eddy currents are calculated and expressed not only as a function of the ratio of domain wall spacing to sheet thickness, but also as a function of the ratio of the domain wall width to sheet thickness As the wall thickness decreases the power loss in the wall is observed to approach zero while the power loss density approaches a constant value