Showing papers on "Single domain published in 1976"

Interacting single-domain properties of magnetite intergrowths

Abstract: Recognition that magnetite intergrowths are a common carrier of stable remanence in igneous rocks has prompted a detailed investigation of their magnetic properties. A Tertiary basalt containing homogeneous titanomagnetite grains was oxidized in air to form magnetite/ilmenite intergrowths, the morphology of which has been studied by electron microscopy. The intergrown grains are shown to contain arrays of interacting single-domained magnetites with uniaxial shape anisotropy. Interactions between single domains cause reduction of coercivity from the very large values associated with isolated single domains to values which are, however, many times larger than those measured in multidomained grains. The intergrown grains have an observed IRS/IS value of 0.30, whereas the value of this ratio obtained experimentally under nondemagnetizing conditions is found to be 0.51. The reduction is shown to be entirely explicable in terms of localized array demagnetizing fields arising from surface poles. A similar effect is seen in magnetite/ulvospinel intergrowths. Qualitative evidence that this reduction proceeds mainly by rotation of the spontaneous magnetization from easy axes is seen in a measured anisotropy of low field axial susceptibility having a value 11% higher in a direction perpendicular to the saturation remanence than that parallel to it. This phenomenon may be used to discriminate between rocks containing interacting single domains and those containing either multidomains or noninteracting single domains. These results also apply to magnetic powder experiments reported in the literature, in which reduction in IRS/IS horn 0.5 will occur if single-domained particles of uniaxial anisotropy are clumped together, a situation which is difficult to avoid. Magnetic intergrowth structures commonly observed in subaerial basalts should be regarded as arrays of interacting single-domain magnetite particles capable of carrying a strong remanent magnetization stable over geological intervals of time.

Pseudo-single-domain effects and single-domain multidomain transition in natural pyrrhotite deduced from domain structure observations

Abstract: The domain configuration of primary pyrrhotite in a Devonian diabase was studied using the Bitter pattern technique. Due to the uniaxial symmetry the multidomain grains have a rather simple domain structure. The single-domain multidomain transition occurs at an average particle diameter of 1.6 μm. In the multidomain grains clusters of inclusions seem to produce pseudo-single-domain effects with complicated domain configurations. Such pseudo-single-domain effects are necessary for the interpretation of the magnetically hard component of remanence which cannot be explained by the observed abundance of true single-domain particles alone.

Magnetization, magnetic anisotropy, and domain patterns of Fe80B20 glass

Abstract: The thermomagnetization behavior, magnetic anisotropy, and magnetic domain patterns of ribbons of the newly synthesized Fe80B20 glass have been examined. This glass exhibits a saturation moment of 1.99 μB/Fe atom, a ferromagnetic Curie temperature of 647 K, and a crystallization temperature of ∼660 K. The direction of magnetic anisotropy lies at ∼60° to the ribbon axis in the plane of the ribbon. Large domains, elongated parallel to the ribbon axis, are observed.

The magnetic barkhausen effect

Abstract: When the magnetization of a ferromagnet (in this paper “ferromagnet” will often include “fernmagnet”) is changed under the influence of an applied magnetic field, the magnetization, particularly in the vicinity of the coercive force, is not smooth function of the field but rather shows a structure composed of many individual steps. This structure is evidence of irreversible changes in magnetization and is known as the barkhausen effect. The effect was named after its discoverer who, in 1919, connected a coil surrounding a ferromagnet to a newly invented amplifier and listened to the output of the amplifier with earphones.1

The use of domain observations in understanding and improving the magnetic properties of transformer steels

Abstract: The observation of the domain pattern of 3% grain-oriented silicon-iron (transformer steel) by the Kerr magneto-optic effect has enabled a greater understanding of the basic magnetization processes of this material to be obtained. In this review paper, an attempt is made to describe recent progress in this field of study. The principal commercial criterion of transformer steel is the power loss and therefore many attempts have been made to correlate the domain observations with measured loss. The increased knowledge of the shape of the loss per cycle against frequency characteristic has shown that the anomalous loss is responsible for approximately 50% of the total loss. Experimental results are described which attribute the anomalous loss to many causes such as the occurrence of domain walls, domain wall angles and configuration, variation of wall spacing with lamination thickness, non-uniform and non-repetitive wall motion (pinning), grain size effects, lack of flux penetration (wall bowing) and domain nucleation. In addition, experimental domain observations are described which explain the optimum thickness of transformer steel for minimum loss and the variation of power loss with applied stress.

Magnetic Domain Structure of an Amorphous Fe-P-C Alloy

Abstract: The domain structure of an amorphous Fe80P13C7 alloy ribbon produced by the centrifugal solidification technique was investigated using the magnetic powder pattern technique. Two different types of domains (a maze domain and a 180°-domain) were observed on the specimen surface. The relationship between the domain structure and the magnetization process was also investigated. The results showed that some of the 180°-walls, which ran nearly parallel to the long axis of the ribbon, caused the hysteresis in the magnetization curve, while the maze domain was responsible for the difficulty in obtaining the saturation in magnetization. The maze domain arises probably from the uniaxial magnetic anisotropy having the direction of easy magnetization perpendicular to the surface. This anisotropy seems to be caused by the magnetoelastic coupling between positive magnetostriction and internal stress in the specimen.

Anisotropy and coercivity in SmCo 5 -based compounds

Abstract: The anisotropy of the RCo 5 -based compounds depends not only on the local anisotropies but also on exchange interactions of the Sm and Co sublattices. This result allows an accurate determination of the Sm3+anisotropy in SmCo 5 and SmCo 3.5 Cu 1.5 ; the anisotropic properties of these compounds are discussed in terms of crystal field. The mechanism of domain wall displacement has been studied on a single crystal of SmCo 3.5 Cu 1.5 by means of Kerr effect and high field magnetization measurements. Domain walls are trapped in copper rich regions where exchange and anisotropy are lower. Magnetic aftereffect measurements show that in fact the trapping effect is in competition with a kink creation mechanism. On this basis, the thermal variation of the coercive field of the SmCo 5 -based compound is explained.

Theoretical study of vector magnetization distribution using rotational magnetization model

Abstract: In magnetic recording, the recording fields are essentially vectorial, and the magnetization process in the recording medium has to be analyzed using vector magnetization. From this fact, a vector magnetization distribution in the recording medium must be evaluated by both magnitude and direction of magnetization. This paper describes the vector magnetization distributions obtained by a new method, using reversible and irreversible rotational magnetization model of single domain acicular particles with uniaxial anisotropy. Calculations are done self-consistently at an instant when the head field is applied and after it is removed. Although the results are, at present, limited to the case where the recording medium is standing still, they show quite good agreement with the results of scaled up model experiments, and can clearly explain the demagnetization mechanism in terms of the vector rotation. This new calculation method will, in principle, display its real power in analyzing the dynamical recording process when the recording medium is moving along the head or the head field is changing.

Single crystal magnetization of ErAl2 and interpretation in terms of the crystalline field

Abstract: Measurements are reported of the magnetization of single crystals of ErAl2 between 4.2K and 16K for magnetic fields up to 150 kOe applied along the (111), (110) and (100) directions. The results are interpreted in terms of the crystal field using a two-dimensional molecular-field approach. Within this microscopic description of the magnetization and the related magnetocrystalline anisotropy the authors use only two temperature-independent crystal field parameters and the Curie temperature. A least-square fitting procedure gives B4=1.10*10-4 meV, B6=-1.34*10-6 meV and Tc=14K. With these parameters they obtain good agreement between calculated and measured magnetization curves.

Preparation and magnetic properties of high coercivity strontium ferrite micropowders obtained by extended wet milling

Abstract: Micropowders of strontium ferrite were obtained by extended wet milling (over 1500 h) of an ordinary SrFe 12 O 19 powder prepared by a chemical process from oxalates. The room temperature intrinsic coercive force of the micropowder drastically increased from about 300 Oe (as milled samples) to 6000 - 6500 Oe after removing the stresses and the defects, introduced by milling, by a suitable annealing at 900 - 1000\deg C. This is one of the highest coercive force reported up to the present for isotropic strontium ferrite powder and it nearly approaches the theoretical value for this material. The magnetic behaviour of these powders is well described by the coherent rotation model of Stoner and Wohlfarth for an assembly of single domain particles oriented at random.Isotropic magnet samples were sintered from these micro-powders at 1150°C. The main magnetic properties of the sintered body were: H_{ci}= 4100 Oe and B_{r} = 2000 G. The energy product maximum was estimated at approximately 0.85 MGO.

Inferences on the magnetic domain state of leg 37 basalts

Abstract: Magnetic experiments conducted on leg 37 basement rock include granulometric techniques (study of low- and high-field hysteresis and temperature dependence of initial susceptibility and of magnetization) and the Lowrie-Fuller test. On the basis of these experiments the following inferences were made concerning the magnetic domain structure: The effective particle size of only one sample, basalt from hole 332B, is in superparamagnetic size range. The single sample of peridotite (from hole 334) provided the only evidence for the presence of multidomain particles. The behavior of the remaining (44) samples, all basalts, can be interpreted as being due to single domain particles which in some cases appear to be moderately to strongly cation deficient. Magnetite or titanomagnetite was found to be the only significant magnetic carrier present.

Models for I and T pattern permalloy bars based upon bitter pattern observation of domain wall movements

Abstract: The magnetostatic fields of the I and T pattern Permalloy overlay bars are analyzed by proposing a model based on the Bitter pattern observation of the domain wall structure in Permalloy bars. The magnetic charges that appear on the 90° domain walls are assumed to be the sources of the magnetic fields of the bars. The model has a two-dimensional reaction to an applied rotating in-plane field due to its two-dimensional domain wall movement and the consequent two-dimensional change of magnetic domain pattern inside the bar. The magnetization of the bar is equal to M s the saturation magnetization of the bar at every section of the bar except on the domain walls. The magnetization curve and the magnetic field well B z (bubble drive field) under the overlay bars are calculated and compared to that of the previous models. A qualitative explanation of the rotation of the bubble around the bars is given by the three-dimensional plots of the field well obtained for different orientations of the in-plane field.

Changes in recording tape magnetization produced by stress

Abstract: When mechanical forces are applied to single domain particles that are used in magnetic recording tapes, the resultant stress anisotropy energy alters the magnetized state, producing reversible and irreversible changes. We use four different experimental techniques to measure these changes and analyze the results in terms of the values for the saturation magnetostriction constants (λ s ) and the applied stress (σ x ). The reversible changes in magnetization (M x ) are roughly proportional to \lambda_{s}\sigma_{x} ; the greatest irreversible or loss component occurs when the product of σ x and λ s along the magnetizing axis ( x ) is negative, increasing when major easy axes make large angles with x .

Method for increasing the critical velocity of magnetic bubble propagation in magnetic materials

Abstract: The critical velocity at which magnetic bubbles can propagate within a matic material is increased by establishing an easy axis of magnetization within the material. This axis is either growth-induced or strain-induced. In one embodiment, the material has a curvature imparted to it which places it under a uniaxial strain and this induces the magnetic easy axis.

High-field magnetization for Mn3O4 single crystals

Abstract: DC magnetization measurements at 42 K in applied fields up to 340 kG are re- ported The smooth behaviour of the magnetization curves confirms that the anisotropy may be attributed to the octahedral site Mn ions

A Scanning Electron Microscope /SEM/ study of the magnetic domain structure of iron meteorites and their synthetic analogues

Abstract: Magnetic domain observations were carried out on iron meteorites and on sputter-deposited thin films of meteoritic composition (10, 20% Ni-Fe), by two SEM techniques: 1) high voltage (30kV) backscattered electron mode and 2) low-voltage (2kV) secondary electron image. To confirm and complement these, 3) Bitter-powder patterns were also observed in reflected-light microscopy. High energy SEM magnetic contrast revealed parallel-oriented arrays of stripe domains in kamacite (k) regions, at 60° (for ‹111› face) or 90° (for ‹100› face) to their taenite (t) boundaries, depending on the crystal orientation. Magnetic domain widths ranged from 15-25μm in the Gibeon meteorite (finest octahedrite, 8% Ni-Fe, average k-bandwidth 0.2mm) to 40-80μm in the Odessa meteorite (coarsest octahedrite, 7.29% Ni-Fe, 3.3mm k-bands). Finer domain substructure (-10μm) was resolved by Bitter-pattern microscopy in Odessa, as magnetic grids in each k grain, whose orientation was discontinuous across boundaries. Based on low-energy SEM observations of Gibeon, it appears that each micro-kamacite grain in plessite regions is a single domain. By the same technique, 1-5μm stripe domains separated by ≤0.5μm Bloch walls were resolved in a 20% Ni-Fe film and 0.2-2μum domains with 90° “elbow”-walls, typical of Fe3O4, were observed in a laboratory-produced Fe3O4 film. The much finer scale of magnetic domain structure in meteorites, by comparison with their metallographic-compositional features, may explain the presence of stable paleoremanence in the coarsely crystalline iron meteorites.The application of even higher-voltage (50kV) SEM to similar studies of terrestrial, lunar, and meteoritic materials promises to reveal the bulk domain-structure of their magnetic carriers and may thus afford a better understanding of their paleomagnetic record.

Single-domain theory for the reversible effect of small uniaxial stress upon the initial magnetic susceptibility of rock

Abstract: The phenomenon of small uniaxial stress changing the magnetic susceptibility of rock is of current interest as a possible aid in earthquake forecasting.In this paper, theoretical expressions are de...

Magnetic Torque Study of a Weak Ferromagnet NiS2

Abstract: Magnetic torque curves were measured on a NiS2 single crystal from 4.2 K up to Tc (30 K). The ordinary torque curve shows a large rotational hysteresis. The hysteresis decreases monotonically with increasing temperature and vanishes at Tc. With the use of magnetic annealing technique, the followings are concluded. (1) The easy axis for the weak ferromagnetic (WF) moment is the axis, and even the magnetic field as strong as 21 kG cannot rotate the direction of the WF moment away from the axis. (2) However, the net magnetization can rotate mainly through 90°-wall displacements. The observed rotational hysteresis is due to the irreversibility of the wall displacements. (3) A single domain state for WF moment can be obtained by magnetic annealing along . (4) It is inferred, from the estimation of the effective anisotropy constant, that the weak ferromagnetism of NiS2 must be one of its intrinsic properties.

On the growth and preparation of large single domain KNbO3 crystals for optical storage

Abstract: The preparation of large single-domain, optically homogeneous iron-doped KNbO3 crystals is described. Different methods of influencing the iron valency are compared.

Domain texture and dielectric constant variations observed along ferroelectric loops of a pure triglycine sulphate crystal

Abstract: The modification of domain texture in triglycine sulphate (TGS) is observed during different ferroelectric loops. Nucleation and domain wall motions are easily observed and they generally involve a small number of domains except at high frequencies. The dielectric constant shows important variations along the loop from e = 28 to e = 55 at room temperature and at low frequency (0.005 Hz). The smallest value corresponds to one single domain and a high dc field (2.8 MV/m), the highest one to a polydomain crystal. At higher frequencies the number of domains and the maximum of the dielectric constant are much higher (i.e. e = 260 at 1600 Hz).

Influence of Wall Coercivity on Magnetization Process of Stripe Domain in MnBi Films

Abstract: The domain configuration and the magnetization process in MnBi films are studied with the aid of the magneto-optic Kerr effect. The pattern period or the average width of reversed and unreversed stripe domains as well as the technical magnetization show a hysteresis phenomenon with respect to the external magnetic field. The pattern period for the same net magnetization is shorter for the ascendant magnetization curve than for the descendant one. The hysteresis phenomena including the minor loop of magnetization are well interpreted by a modified stripe domain theory which takes the effect of the domain wall coercivity into consideration.

Direct measurement of stray magnetic field distributions from a magnetic bubble domain in yttrium orthoferrite with a micro Hall element

Abstract: The stray magnetic field distributions from an isolated magnetic bubble domain of about 150-µm diameter in YFeO 3 are measured by a micro Hall element made of a single crystal InSb with active dimensions of 5 × 5 × 2.6 µm3. Experimental results for an isolated bubble domain show fair agreement with the theoretical ones for a cylindrical bubble domain.

Magnetooptical investigation of the permalloy overlay at micron resolution

Abstract: The distribution of magnetization M in T and I elements at various orientations and values of external magnetic field H was investigated. It has been discovered that there is a strong mutual influence of adjacent bars on the distribution of M in T- and I-bars. Direct observations of the magnetization distribution in the I-bar in the presence of bubble field were performed.

Field and temperature dependence of magnetization of U3P4

Abstract: We conclude that the occurrence of a maximum in the magnetization versus temperature curve observed under certain circumstances on U3P4 is not connected with its intrinsic magnetic structure, but substantially depends on the form in which the material is studied (polycrystalline powder, single crystal, single crystal powders with various dimensions of grains). This phenomenon seems to be affected by “quenching” of the state from the region of low anisotropy at higher temperature in the small particles with a strong tendency to single domain behaviour and thus it may be a consequence of rotation magnetization process in the fields relatively small for U3P4. The assertion about transitions between magnetic ordering, sometimes proposed in the literature on the basis of observed anomalies in the temperature course of magnetization without simultaneous confirmation by neutron diffraction, should be accepted with some reservation, especially in the case of simple uranium compounds. However, another situation arises for pseudobinary alloys of ferro- and antiferromagnetic components (e.g. UP0·75S0·25) where such transitions were confirmed both by magnetic methods and by neutron diffraction studies [13].

Interactions of Mobile Impurities with a Single Domain Wall in Iron Whiskers

Abstract: The magnetic after effect is studied by measuring the magnetic response of an iron whisker with a single 180 degree wall in the presence of mobile interstitial atoms. The frequency dependence of both the in phase and out phase component of the small amplitude a.c. susceptibility are fitted to an exponential memory function with a single time constant at each temperature. The interactions of the wall with impurities is used also to investigate the properties of the wall.

Dynamic Behavior of Magnetization Ripple in High Speed Switching in Magnetic Thin Films

Abstract: Dynamic behaviors of the magnetization ripple in magnetic thin films are studied by means of solving the Landau-Lifshitz-Gilbert equation of motion numerically. In solving the equation, the exchange interaction and the magnetostatic interaction due to the spatially inhomogeneous distribution of the magnetization in addition to the anisotropy field and the external field are taken into account as the effective magnetic field. The oscillation of the magnetization ripple, caused by the sudden application of driving pulse fields, is excited parametrically and built up remarkably by the varying effective field associated with the rotational motion of the magnetization. It is found that the difference of the rotation angle between the most leading and the most lagging portions can be so large as to reach about 50° in the rotational process of the magnetization.

Stripe domain structure of (001) magnetic films with positive constant of crystalline anisotropy

Abstract: The peculiarities of nucleation of stripe domain structure and the form of the magnetization curve of single crystal films of (001) type, with a positive constant of crystallographic anisotropy, which have so-called perpendicular anisotropy are considered The conditions are found under which the magnetization jumps are possible due to the effect of magnetic crystallographic anisotropy on the reversal magnetization process in the films investigated A qualitative comparison of the theory with experiment is carried out [Russian Text Ignored]