Showing papers on "Single domain published in 1979"
TL;DR: A review of the current state of the research work on soft magnetic materials can be found in this article, where it is shown that the displacement of domain walls is described fairly well by the conventional potential theory developed previously for crystalline materials.
223 citations
TL;DR: In this paper, a theoretical model of grain size dependence of domain transitions in magnetite is presented, which is used to predict the grain size range for pseudosingle domain (PSD) behavior.
Abstract: A theoretical model of grain size dependence of domain transitions in magnetite is presented. This domain model is used to predict the grain size range for pseudosingle domain (PSD) behavior in magnetite. For cubic magnetite particles, the single domain (SD) to two-domain (TD) transition occurs at ∼800 ± 200 A, the TD-three-domain transition occurs at ∼ 1500 A, and the PSD-"true" multidomain (MD) transition occurs at \sim 8\mu m. These results are in fair agreement with experimental results within a factor of 2. Our results indicate that the grain size range for the canonical case of a PSD grain (a TD grain with a single 180° wall) or "PSARK" (subdomain magnetic moment) ranges from ∼700 A for cubic particles of magnetite to \sim3.2 \mu m for a length: width ratio of 5:1. Comparison with grain size distributions of magnetite grains in igneous rocks suggest that the PSARK can be the major contributor to the remanence of these grains.
85 citations
TL;DR: In this paper, the authors considered a 3D domain wall in a cubic lattice with two-dimensional rotators and showed that the wall undergoes a phase transition in the K, T plane, the order parameter being the chirality.
Abstract: 2014 We study a domain wall in a three dimensional XY model as a function of anisotropy (K) and temperature (T). It is shown that the wall undergoes a phase transition in the K, T plane, the order parameter being the chirality. Thus it is a two state system analogous to an Ising system. The phase transition can be of the second order and exhibits soft modes. In the ordered state the wall can exhibit domains of opposite chirality separated by singular lines. LE JOURNAL DE PHYSIQUE LETTRES TOME 40, 1 er AVRIL 1979, Classification Physics Abstracts 75.10 75.60 We consider a three dimensional XY [1] model (n = 2) with two dimensional rotators, the rotation axis being the Z direction. The rotators are located at the vertices of a simple cubic lattice, the interaction being between first neighbours. The Hamiltonian of the system can be written : 0~ : angle between Si and the Y axis i : represents the three-dimensional (p, q, r) indices. When we vary the temperature this system undergoes a bulk phase transition ferromagnetic ordering which, because of the anisotropy K, is of Ising character (n = 1 ). Let us consider a domain wall perpendicular to the Z direction at T = 0. When K is large, the domain wall width, 5, is of the order of a ~/7/~ (a : lattice parameter) ; so this relation loses its meaning when 5 is smaller than A(JIK 1) [2]. In this regime (J/K 1), the domain wall is one unit cell spacing, the spins being up for Z 0 and down for Z ~ 1 (up refers to the Oy direction). Let us call this configuration (I). The equilibrium conditions for the wall are : with the boundary conditions : Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:01979004007016500 L-166 JOURNAL DE PHYSIQUE LETTRES These conditions are fulfilled in (1) because 0~ = 0 or 7r. To investigate its stability let us now study small movements around this configuration. The equations of motion are : (I is the moment of inertia of each rotator). Let us writer = 0? + gi (e° equilibrium angles) and linearize (3) :. obviously the solutions have the form For a given value of K)j, we have a full spectrum consisting of a localized mode (in the Z direction), D~ and a branch of delocalized modes O)KII (Kl.) :
68 citations
TL;DR: In this paper, the principles of micromagnetics are used to describe the magnetization processes and magnetic configurations in a cylinder of finite length, which is made possible by propagating point singularities down the axis of the cylinder.
Abstract: The principles of micromagnetics are used to describe the magnetization processes and magnetic configurations in a cylinder of finite length. The cylinder is of radius large compared to the exchange radius. Magnetostatic terms dominate in the limit that crystalline anisotropy is negligible. The exchange energy is minimized for boundary conditions primarily determined by magnetostatics. The point singularities required by topology are essential to understanding the process of magnetization. Complete reversal of magnetization is made possible by propagating point singularities down the axis of the cylinder. These propagating singularities arise from pair creation in a unit vector field.
58 citations
TL;DR: In this paper, a basalt sample dredged from the axis of the Mid-Atlantic Ridge has been ion-thinned and examined by transmission electron microscopy, and fine dispersed particles as small as 0.04μm in diameter, occurring in amorphous patches of the rock, have been identified as titanomagnetite by means of electron diffraction and microanalysis.
Abstract: A basalt sample dredged from the axis of the Mid-Atlantic Ridge has been ion-thinned and examined by transmission electron microscopy. Finely dispersed particles as small as 0.04 μm in diameter, occurring in amorphous patches of the rock, have been identified as titanomagnetite by means of electron diffraction and microanalysis. These small particles have dimensions appropriate to single magnetic domain behaviour, and are considered to be largely responsible for the strong and very stable natural remanent magnetization of this rock.
40 citations
TL;DR: The critical field for unpinning or nucleation of a domain wall in a ferromagnetic crystal at an antiphase boundary (APB) is calculated as a function of the magnetic coupling constant η across the APB as discussed by the authors.
Abstract: The critical field for unpinning or nucleation of a domain wall in a ferromagnetic crystal at an antiphase boundary (APB) is calculated as a function of the magnetic coupling constant η across the APB. It turns out that for positive values of η pinning occurs and that for negative values there is very strong pinning and also nucleation.
37 citations
TL;DR: In this paper, it is shown that the magnetic behavior of titanomagnetites is similar to a spin glass, which is interpreted as a transition of optimum single-domains going over to superparamagnetic state.
Abstract: It is shown that hysteresis and susceptibility studies at various temperatures could provide an idea whether a magnetic sample contains multidomain, single-domain or superparamagnetic particles. Our results on titanomagnetites with those of others on cobalt substituted magnesium ferrites suggest that domain wall formation is inhibited in some of them whereby only single-domain or superparamagnetic particles occur irrespective of the physical grain size of such materials. At high concentration of titanium in titanomagnetites, the magnetic behaviour is similar to a spin glass, which we interpret as a transition of optimum single-domains going over to superparamagnetic state.
36 citations
TL;DR: In this article, the magnetic moments, easy directions and hard axis magnetization behavior in high magnetic fields have been studied in detail on single crystals of the quasibinary compounds Y 1-x Nd x Co 5, Y 1 -x Gd X Co 5 and Tb x Y 1x Co 5+0.1x at temperatures of 4.2 -400 K.
Abstract: The magnetic moments, easy directions and hard axis magnetization behaviour in high magnetic fields have been studied in detail on single crystals of the quasibinary compounds Y 1-x Nd x Co 5 , Y 1-x Gd x Co 5 and Tb x Y 1-x Co 5+0.1x at temperatures of 4.2 - 400 K. The easy directions of Gd-compounds remain parallel to their c-axes throughout the whole temperature range. The spin reorientations from c-axis to c-plane take place during cooling of Nd- and Tb-compounds at temperatures which are the higher, the larger is x. The hard direction magnetization curves at 4.2 K were used for calculating the first and second anisotropy constants of the rare earth magnetic sublattices as well as molecular fields acting on rare earth ions from the cobalt sublattice. It is shown that magnetocrystalline anisotropies of Nd- and Tb-sublattices are well described in terms of the single-ion model while Gd-sublattice has negligible anisotropy energy. The influence of magnetocrystalline anisotropy on spontaneous magnetic moments of both sublattices at 4.2 K is shown for Y 1-x Tb x Co 5+0.1x compounds.
32 citations
TL;DR: In this article, a variational method was developed to calculate the separation of stray field energy which would be present even with an infinitely thin wall, and the results showed that isolated charged walls do exist if exchange energy is taken into account, as opposed to the periodic solution known for the limit of negligible exchange energy.
Abstract: Charged walls are domain walls which carry a net "magnetic charge" (div M) due to their orientation relative to the domain magnetizations. They differ from ordinary Bloch and Neel walls (which are uncharged) primarily in their much wider profile. In order to calculate such walls, a variational method was developed. It is based on the separation of that part of stray field energy which would be present even with an infinitely thin wall. The main results of the calculations are as follows. 1) Isolated charged walls do exist if exchange energy is taken into account, as opposed to the periodic solution known for the limit of negligible exchange energy. 2) Rotated, partially charged walls develop a Neel-wall-like narrow core region. Detailed results for the wall profiles, energies and widths as a function of wall angle, orientation, film thickness, and material parameters are presented. They are applied to two examples: the case of a Permalloy film in a domain tip propagation memory, and the case of the implanted layer on a contiguous disk bubble device.
32 citations
TL;DR: In this paper, conditions of stability of the magnetization curling mode in fine spherical and cylindrical particles were derived, and magnetization reversal processes in such particles were considered, and the application of Ritz's method for solving the variational problem of finding the local magnetization vectors in the volume of a particle provided a convenient way of finding conditions mentioned above.
Abstract: Conditions of stability of the magnetization curling mode in fine spherical and cylindrical particles and of the magnetization helicoid structure in fine cylindrical particles are derived, and magnetization reversal processes in such particles are considered. The application of Ritz's method for solving the variational problem of finding the local magnetization vectors in the volume of a particle provides a convenient way of finding the conditions mentioned above. It has been shown that the magnetization curling mode in a spherical fine particle with radius larger than a critical one is stable in a well-determined interval of the external magnetic field, provided the magnetocrystalline anisotropy constant is less than a certain value K 0 . In such a case the hysteresis loop of a spherical particle measured in an easy direction is no longer rectangular. The magnetization curling and helicoid modes are both unstable in fine cylindrical particles with positive or zero values of the magnetocrystalline anisotropy constant. The hysteresis loop of such particles magnetized along the axis of rotation is rectangular.
26 citations
TL;DR: In this article, a theory for intrinsic coercivity in a narrow magnetic domain wall material is proposed, where results from non-linear mathematics are used to represent magnetic domain walls as solitary-wave or soliton excitations.
Abstract: A theory for intrinsic coercivity in a narrow magnetic domain wall material is proposed. Results from non-linear mathematics are used to represent magnetic domain walls as solitary-wave or soliton excitations. By applying the perturbation of a discrete lattice to the continuum sine-Gordon equation, a scattering (pinning) of the soliton (domain wall) is obtained, with a strong onset occurring when the domain wall width becomes comparable with a few lattice spacings. Correlation between this effect and the intrinsic (i.e. not defect dependent) coercivity is made. Specific examples are given using the RCo5xNi5-5x and RCo5xCu5-5x systems which exhibit narrow domain walls.
TL;DR: In this article, the sign change of the magnetocrystalline anisotropy constant is discussed in connection with a sign change in the easy direction of magnetization in the temperature range from about 240°C to about 380°C.
Abstract: Domain structures as a function of temperature observed on various crystallographical planes of h.c.p. cobalt single crystals are discussed in connection with the sign change of the magnetocrystalline anisotropy constant. The present observation indicates that there are two regions with the easy axis either parallel to (C// domain) or normal to (C⊥ domain) the c-axis, in the temperature range from about 240°C (Ku1≈0) to about 380°C (Ku1<0). The change in volume ratio of the two regions is responsible for the gradual change in the resultant easy direction of magnetization in this temperature range.
TL;DR: In this article, the relationship between the position of charged walls and the bubble motion around propagation circuits is discussed, and long walls which extend between adjacent propagation loops are revealed by the Bitter technique.
Abstract: The relations between the position of charged walls and the bubble motion around propagation circuits are discussed. Long walls which extend between adjacent propagation loops are revealed by the Bitter technique. The examination of the domain structure in the implanted layer shows the existence of a magnetic gradient which is a function of the distance from the propagation circuits. The switching of magnetization in particular directions of the in-plane field is reported and correlated with the bubble movement. An additional easy axis is observed along the circuits due to shape anisotropy. Propagation margins are very similar to those obtained with permalloy circuits. Fabrication technology as well as design of 16 μm period circuits is discussed. Nucleation and transfer have been achieved with currents in the range of 50 mA to 200 mA. Phase margins of about a quarter of a period are found, and bias field margins fall between 10 and 15 Oe.
Patent•
16 Jul 1979
TL;DR: The magnetization vectors of the thin film structures are opposite with respect to each other, thereby to preclude, or at least lessen, demagnetization fields associated with the structures as mentioned in this paper.
Abstract: Flux sensitive apparatus, in one form thereof, employs paired thin single domain magnetic film structures, the easy magnetization axes of which are canted with respect to the direction of sense current flow therewithin. The magnetization vectors of the film structures are opposite with respect to each other, thereby to preclude, or at least lessen, demagnetization fields associated with the structures. By special connections between the thin film structures, the respective sense currents therein are provided with the same spatial direction of flow; and mutual biasing of the structures is thereby avoided.
TL;DR: In this paper, some problems encountered in these types of calculations are discussed and some solutions of certain micromagnetic problems using digital computers have been attempted in the past decades and these problems are becoming increasingly important as magnetic devices such as magnetic bubbles, are built which require high resolution.
Abstract: Solutions of certain micromagnetic problems using digital computers have been attempted in the past decades. These problems are becoming increasingly important as magnetic devices, such as magnetic bubbles, are built which require high resolution. Some problems encountered in these types of calculations are discussed.
Patent•
24 May 1979TL;DR: In this article, a method of manufacturing plastic-bonded anisotropic permanent magnets, agglomerates having an easy axis of magnetization in a size from 300 to 1000 μm are used as a magnetic material in a mixture with single magnetic domain particles.
Abstract: In a method of manufacturing plastic-bonded anisotropic permanent magnets, agglomerates having an easy axis of magnetization in a size from 300 to 1000 μm are used as a magnetic material in a mixture with single magnetic domain particles. In this manner a particularly large packing density of magnetic material in the permanent magnets is obtained. With a filling of the mixture of plastic-binder with magnetic material in the order of approximately 75% by volume, remanence values are realized above 310 mT.
TL;DR: In this paper, a review of theoretical investigations into the influence of domain structure and dynamic behaviour of domain walls on some low and high-frequency properties of ferromagnetic materials is presented.
Abstract: A review is presented of theoretical investigations into the influence of domain structure and dynamic behaviour of domain walls on some low- and high-frequency properties of ferromagnetic materials, The effect of dynamic bowing of domain walls on electromagnetic losses in electrical steel is analyzed in detail. The theories of Pry, Bean and Bishop are generalized to explain experimentally observed nonlinear dependence of eddy-current power losses on frequency and wall spacing. A study is made of the influence of domain structure on the parametric excitation of spin waves with account being taken of domain wall structure. It is shown that the lowest parametric excitation threshold corresponds to spin waves within domain walls and that the parametric excitation effect is rather sensitive to domain wall structure. The influence of a characteristic domain structure arising on the basis of a twinning structure of magnetically ordering alloys on the Mossbauer spectra is analyzed. It is shown that the observed special features of these spectra may be explained on the basis of this domain structure.
TL;DR: In this article, a theory for the frequency dependence of low-field absorption of microwave energy by magnetic garnet films containing a stripe domain structure was proposed, and the ratio of this magnetic moment to the r.f. moment of the uniform mode was calculated and observed to be in good agreement with the experimental results.
Abstract: A theory is proposed to account for the frequency dependence of the low field absorption of microwave energy by magnetic garnet films containing a stripe domain structure. Considering only the uniaxial anisotropy field Hu and the demagnetization energy a Schrodinger like equation for the r.f. magnetization has been developed. Unbound states, for ω/γHu≳1, develop a net moment across a domain wall which couples in a non‐resonant manner to an r.f. magnetic field. The frequency dependence of this coupling is calculated by box normalizing the solutions of the Schrodinger like equation. The ratio of this magnetic moment to the r.f. moment of the uniform mode is calculated and observed to be in good agreement with the experimental results.
TL;DR: In this article, the authors employ a similar method of analysis to study two-dimensional resonance modes in a thin film contaning a single magnetic bubble, where the thickness of the bubble domain wall is ignored, and there is no applied gradient.
Abstract: We have recently discussed magnetostatic modes in a normally‐magnetized, thin‐film disk that are bound to ’’virtual‐surfaces’’ created by the presence of a radial dc‐field gradient; the frequency and polarization of such modes was found to be sensitive function of the gradient. We now employ a similar method of analysis to study two‐dimensional resonance modes in a thin film contaning a single magnetic bubble. When the thickness of the bubble domain wall is ignored, and there is no applied gradient, the spectrum, as expected, contains single bubble resonances coupled to disk resonances. However, actual domain walls contain large magnetic anisotropy field gradients due to the often complex spin reversal pattern. Such gradients will affect the mode polarization within the wall and the effective boundary conditions acting across the wall may be significantly altered for those resonances coupled to exchange modes within the domain wall. The related but simpler problem of rf exchange modes generated at a plane ’’virtual‐surface’’ within a single domain region is studied in detail.
TL;DR: In this paper, it was found that spin flopping in NiWO4 is a first order phase transition and the domain layer directions make an angle with the vector of the inducing magnetic field, which can be varied by minor changes in the external field direction.
Abstract: A strong external magnetic field, Hc=176 kOe, applied along the ordering axis of antiferromagnetic NiWO4 produces spin flopping. This orientational transition results in sharp changes both in longitudinal and transverse components of the magnetization vector. It is found that for certain external magnetic field orientations, spin flopping in NiWO4 is a first order phase transition. The measurement results for magnetic properties suggest that an intermediate state appears in this field region, where the sample laminates into magnetic domains. The domain layer directions make an angle with the vector of the inducing magnetic field, which can be varied by minor changes in the external field direction.
TL;DR: In this paper, the behavior of the time lag of magnetization of normalized β′−NiAl phase under a 15kOe applied magnetic field was studied and the magnetic relaxation process followed the Voigt-Kelvin type of anelastic behavior, from which the relaxation time τ=4.73 min was obtained.
Abstract: The behavior of the time lag of magnetization of normalized β′‐NiAl phase under a 15‐kOe applied magnetic field is studied. The time‐dependent creep magnetization curve does not fit the parabolic relation which describes the diffusion process of the magnetic moments. The magnetic relaxation process followed the Voigt‐Kelvin type of anelastic behavior, from which the relaxation time τ=4.73 min was obtained.
01 Jan 1979
TL;DR: Schoenharting et al. as discussed by the authors investigated the magnetic properties of rocks from the Geitafell gabbro complex, SE Iceland, and found that anomalously strong NRM of reversed polarity exists in this zone up to 5 vol%.
Abstract: DGF Schoenharting, G.: Magnetic properties of rocks from the Geitafell gabbro complex, SE Iceland. Bull, geol. Soc. Denmark, vol. 28, pp. 21-29, Copenhagen. October 23rd, 1979. The southern portion of Geitafell gabbro, SE Iceland, has been sampled in detail along a horizontal profile of 1.5 km length for rock magnetism analysis. Within this profile a ca. 200 m wide zone exists with anomalously strong NRM of reversed polarity. Magnetite enrichment in this zone up to 5 vol% cannot alone account for the large NRM values. Oxidation exsolution of ilmenite in titanomagnetites and, less important, reduction exsolution of magnetite in ilmenites as well as formation of magnetite from silicates are considered the cause of the strong magnetization. During these processes at high temperatures small magnetite grains have been formed with »pseudo single domain« (psd) magnetic properties. Small stability of NRM during AF demagnetization rules out »single domain« grains and is interpreted as result of interaction between psdand »multi domain« magnetic moments. The rocks studied have preserved their paleomagnetic directions since cooling. It is suggested that such rocks might contribute to marine magnetic anomalies.
TL;DR: In this paper, the authors present an explanation of the phenomenon in terms of migration of cation vacancies from the interior of a magnetic domain to a domain wall in a magnetized γFe 2 O 3 particle, thereby decreasing the free energy of the system.
Abstract: Some γFe 2 O 3 -based magnetic recording tapes, particularly those using larger particle size γFe 2 O 3 , tend to retain a low-level or latent residual recorded signal after erasure with a large alternating magnetic field. The residual signal effect increases with time and temperature of storage after recording. The effect varies with the FeO content of the γFe 2 O 3 particles, and is a maximum at an FeO content of about 10 percent by weight. An explanation is presented of the phenomenon in terms of migration of cation vacancies from the interior of a magnetic domain to a domain wall in a magnetized γFe 2 O 3 particle thereby decreasing the free energy of the system. This sets up concentration gradients of Fe2+ions in regions of domain walls which remain after demagnetization of the tape and results in some residual magnetization. Reasonable agreement is obtained between calculated and observed residual magnetic effects as a function of FeO content.
TL;DR: In this paper, a chemical method of producing a hard magnetic layer around low-coercivity channels was studied from the viewpoint of their ability to provide functionally stable propagation of flat magnetic domains.
Abstract: Static magnetic characteristics and film surface structure were studied in a chemical method of producing a hard magnetic layer around low coercivity channels. Applicability of the channels obtained was studied from the viewpoint of their ability to provide functionally stable propagation of flat magnetic domains. Probability of a false domain occurrence in propagation steps strongly depends upon the coercivity of the hard magnetic layer, magnetic properties, and shape of the low-coercivity channels and the parameters of the control fields, and may he well described by the exponential law in the area of small values for one transfer cycle per one bit (P1/1). Certain types of channels with certain values of hard magnetic layer coercivity and domain nucleation field have an area in which the value of the required erase field is practically independent of the propagation field. The study and computations show that the chemical method is capable of providing sufficiently low values of P1/1. The mechanism of false domain occurrence was not studied.
TL;DR: The magnetic susceptibility of small single-domain nickel particles chemisorbed on a silica carrier has been studied as a function of temperature in the range 1.7 < T < 700K as mentioned in this paper.
TL;DR: In this paper, the authors measured the domain wall motion and flux patterns in vacuum-deposited thin film cores by using the Kerr magnetooptic effect and found that the thin film has the domain configuration which depends on the distribution of applied magnetic field.
Abstract: Domain wall motion and flux patterns in vacuum-deposited thin film cores were observed under dc and pulsed magnetic fields by using the Kerr magnetooptic effect. Two of the thin film cores have a uniaxial magnetic anisotropy around the circumference, and the other is magnetically isotropic. The domain configuration with current through the center of the hole is circular, and expands radially. Domain wall position was quantitatively measured as a function of dc and pulse current. Circular multi-domain walls like an onion slice appear by switching the polarity of the current, and are moved by the pulse field. By exciting the thin film cores with a drive winding, a notched domain appears without continuity of magnetic flux, but the thin film coated on the permalloy bulk core has a circular domain with continuity of flux. From these results, it is confirmed that the thin film has the domain configuration which depends on the distribution of applied magnetic field, and that the thin film coat transcribes the domain wall motion in the bulk core.