Showing papers on "Single domain published in 1989"

The 40Ar/39Ar thermochronometry for slowly cooled samples having a distribution of diffusion domain sizes

Abstract: Many 40Ar/39Ar age spectra for alkali feldspars are significantly different from the model age spectra calculated for slowly cooled samples composed of diffusion domains of a single size, and the Arrhenius plots for these samples show departures from linearity that are inconsistent with diffusion from domains of equal size. The most plausible explanation for these discrepancies is the existence of a distribution of diffusion domain sizes. We have extended the single-diffusion-domain closure model of Dodson so that it applies to minerals with a distribution of domain sizes and have used it to explain many commonly observed features of 40Ar/39Ar age spectra and Arrhenius plots for 39Ar loss during step heating. For samples with a distribution of diffusion domain sizes, the form of the 39Ar Arrhenius curve is a function of the heating schedule (i.e., the temperature and duration of the steps used), and thus different heating schedules will result in different curves for the same sample. This effect can be used to confirm the existence of a distribution of diffusion domain sizes and to optimize the information contained in the Arrhenius plot. The multiple diffusion domain size model is used to reinterpret the age spectra, Arrhenius plots, and cooling history of three feldspars from the Chain of Ponds pluton, northwestern Maine, earlier interpreted assuming a single domain size. Interpreting the 40Ar/39Ar and 39Ar released during step heating in terms of a single domain size gives rise to a large discrepancy between the cooling rate determined from the age and closure temperature of the three samples compared to the cooling rate required to explain the shape of the individual age spectra. The single domain size model fails also to account for the observed departures from linearity of the Arrhenius plots. We show that a particular domain size distribution in each sample can explain in detail both the shape of the age spectra and the Arrhenius plots, and results in the three samples defining a common cooling history. There is thus good evidence for the three alkali feldspar samples studied here that the thermally activated diffusion measured by 39Ar release during step heating in the laboratory is also the mechanism responsible for argon loss or retention in the natural setting.

Low-field magnetic response of complex superconductors.

Abstract: Solutions of the Ginzburg-Landau equations for a complex superconducting phase are presented for regions close to a domain wall and to the surface. The finite local magnetization found at these inhomogeneities yields a small magnetic response via a movement of domain walls in an external magnetic field. We examine line defects in the walls which are vortices enclosing a fraction of the universal flux quantum.

An analysis of perpendicular magnetic recording using a newly developed 2D-FEM combined with a medium magnetization model

Abstract: In order to analyze perpendicular magnetic recording mechanisms, the authors have developed a 2-D FEM (finite-element method) simulation program in which a vectorial magnetization of magnetic particles is introduced into the calculation of magnetization distributions in a recording media. This program makes a physically accurate simulation of magnetic recording and reproducing processes because not only the magnetic nonlinearity of head and medium but also the head-to-medium magnetic interaction are taken into account. It is confirmed quantitatively by the program that stronger head-to-medium magnetic interaction produces a sharper magnetization transition and a higher reproduced voltage at higher recording densities. >

High-Field Magnetization in PrCo 2 Si 2 Single Crystals

Abstract: Magnetic properties of PrCo 2 Si 2 single crystals have been studied by measurements of high-field magnetization, magnetic susceptibility and electrical resistivity. Anomalous behaviors in the resistivity appear at three successive magnetic phase transition temperatures of 9, 17 and 30K. The magnetic susceptibility is highly anisotropic and is analyzed using the single-ion Hamiltonian, including the crystal-field and molecular-field effects. The thermal variations of the susceptibilities can be well reproduced by the crystal-field parameters estimated from the point-charge model. Metamagnetic transitions with four steps are observable in the c -axis magnetization process up to 300 kOe. The magnetization process is discussed in terms of the incommensurate exchange field model in the Ising system proposed by Date.

A method for obtaining single domain superconducting YBa2Cu3O7−x single crystals

Abstract: A method is reported for producing an orthorhombic YBa2Cu3O7−x single crystal comprised entirely of a single untwinned domain. The transformation from a polydomain to a single domain single crystal is carried out by applying uniaxial pressure of approximately 25 MPa for about one minute at 450°C in an oxygen atmosphere. We report on some of the superconducting properties of crystals produced in this way.

Biogenic and lithogenic magnetic minerals in Atlantic and Pacific deep sea sediments and their paleomagnetic significance

Abstract: The carrier of the natural magnetization of deep sea sediments was characterized by mineralogical, electron microscopic, and rock magnetic investigations. Magnetic single domain (SD) and pseudo single domain (PSD) particles which are most important for the stable remanent magnetization were separated from the magnetic »coarse fraction« and concentrated as magnetic »fine fraction«. The magnetic coarse fraction consists of lithogenic magnetite and titanomagnetite, which often contains exsolution-lamellae of ilmenite. Both minerals are partially maghematized and occur isolated in the sediment or embedded in rock particles, in regionally different concentrations. The magnetic fine fraction consists of lithogenic magnetite and titanomagnetite and biogenic magnetite (magnetofossils = fossil bacterial magnetosomes), the latter generally maghematized.

Magnetoresistive head and head setting method

Abstract: A method of establishing a single domain in a magnetoresistive sensor positioned in a gap between two shield layers of magnetic material. The method includes the steps of heating the magnetoresistive head above the Neel temperature of at least one of the shield layers of magnetic material. Applying an external magnetic field to the magnetoresistive sensor and the shield layers for establishing a single magnetic domain in the magnetoresistive sensor. Reducing the intensity of the external magnetic field for holding the magnetization of the magnetoresistive sensor during cooling. Cooling the magnetoresistive head.

On the computation of particle demagnetizing fields

Abstract: The nonuniform demagnetizing fields of a magnetic particle are computed. It is shown that the dipole-dipole approximation introduces large errors only for the nearest neighboring elements, and they can be corrected by numerical integration over the surface charge of each element. The coercivity and the squareness ratio are calculated as functions of the particle aspect ratio and width. The coercivity is found to saturate at a smaller aspect ratio than that of the ideal spheroids. The remanent magnetization transforms from a uniform state to a vortex state at a characteristic particle width regardless of the particle length. However, longer particles have higher squareness ratios. >

Model of growth of single‐domain GaAs layers on double‐domain Si substrates by molecular beam epitaxy

Abstract: Growth of single‐domain GaAs (100) layers on double‐domain Si (100) substrates by molecular beam epitaxy has been investigated. It has been shown that domain orientation of the top layer of GaAs depends on the surface structure of a buffer layer. The size of atomic step heights on the Si surface and the As‐Si interaction temperature before film growth are not important factors in controlling domain orientation. Suppression of an antiphase disorder is explained in terms of nonstoichiometric antiphase boundary annihilation operative during growth.

Domain control method for nonlinear ferroelectric optical material

Abstract: PURPOSE: To eliminate the need for impression of a voltage and to avoid the failure in a crystal generated by the flow of current and the degradation in purity by the diffusion of an electrode material by disposing absorbers or reflectors of electromagnetic waves for heating a nonlinear ferroelectric optical material to be formed with domain inversion structure parts on one main surface of this optical material. CONSTITUTION: The substrate of a Cherenkov radiation type light second harmonic wave generating element having the periodic domain inversion structure parts is constituted of the crystal of lithium niobate having a large nonlinear coefft. and a C-axis in the thickness direction of the crystal at the time of forming the above-mentioned element. Namely, the optical material 1 formed as the single domain having the C-axis in the thickness direction is prepd. The material is heated up to the temp. below the Curie point thereof. for example, up to about 1,200°C and the external DC voltage is impressed in the thickness direction thereof to generate the domains unified in the thickness direction of the C-axis at the time of forming the above-mentioned material as the single domain. The absorbers or reflectors 2 consisting of Pt having the heat resistance to heat rays for heating are previously provided in the form of stripes on one main surface 1a of material 1 and the polarization inversion is generated by the voltage generated by the pyroelectric effect. COPYRIGHT: (C)1991,JPO&Japio

High-field magnetization process in ferrimagnetic R2Fe14C compounds-interplay of molecular and crystal fields

Abstract: The magnetization process in magnetic fields up to 40 T of ferrimagnetic R2Fe14C compounds (R=Gd, Tb, Dy, Ho, Er, Tm) has been studied by considering the field-induced non-collinearity of the magnetic structure. Inter-sublattice molecular fields as well as the exchange coupling between 3d and 4f spins have been evaluated. The high-field susceptibility of Gd2Fe14C and Lu2Fe14C has been examined in detail. Magnetovolume phenomena are found to affect strongly the magnetic properties of these iron-based compounds.

Thin film magnetic element having a rhombic shape.

Abstract: The present invention provides increased stabilization of the magnetization of a single domain thin magnetic film (62) over that attainable in the rectangular thin film (16) known in the prior art by shaping the magnetic film (62) as a rhomboid rather than as a rectangle. Practice of the invention teaches angling the transverse sides (68, 70) of the film with respect to the longitudinal sides (64, 66) either at an angle (63) equal to, or smaller than, the angle (72) at the bias point of the magnetization (74) with respect to the direction of the easy axis (51), as established by an external bias field (76). Under these conditions the biased magnetization (74) of the film (62), being either parallel to, or at a positive angle with respect to the transverse sides (68, 70) of the rhomboid, either generates no charges at the transverse edges (68, 70) of the film, or actually generates charges (82, 84) which produce a field parallel to the longitudinal component of the magnetization (74) which stabilizes the magnetization (74) of the single domain rather than destabilizes it.

Experimental verification of Chua type magnetization model

Abstract: A Chua-type magnetization model that is capable of representing the Rayleigh relationship, after effect, and iron loss has been proposed in the literature. It has been pointed out that a model parameter representing hysteretic property depends on the movement of domain walls and is an important factor related to iron loss of soft magnetic materials. The frequency dependence, minor loop, initial magnetization, ferroresonance and transient characteristics of the Chua-type model are examined, comparing theoretical results with experimental measurements. It is confirmed that the model satisfactorily reproduces the typical magnetization characteristics observed in practice. >

Irreversible magnetization and upper critical field of YBa2Cu3O7 single crystals in high magnetic fields

Abstract: A sample of YBa 2 Cu 3 O 7 was constructed by stacking a number of small single crystals. Magnetization measurements were made in magnetic fields up to 38 T, both parallel to the c -axis and to the basal plane. At 1.4, 4.2 and 20.4 K, a large irreversible magnetization was observed. The significance of these results for the superconducting properties is discussed.

Fe-Ni-Nb 系合金薄膜の軟磁気持性

Abstract: Relation between soft magnetic properties and local anisotropy fluctuation in Fe-Ni-Nb alloy films measured by the dynamic differential susceptibility method was clarified and discussed in comparison with Fe-Si-Al alloy films. In Fe-Ni-Nb alloy films, excellent soft magnetic properties, μeff=6500 at 5 MHz of 1000A film thickness, were realized. In Fe-Si-Al alloy films, the magnitude of μeff is proportional to 1/√S (S: structure constant) and independent of the value of HK, while in Fe-Ni-Nb alloy films, the value of S is about one tenth of that in Fe-Si-Al alloy films, and the magnitude of μeff is not dependent on the value of S. Rather, this magnitude is dependent on the value of Hk, and is almost equal to 4πMs/Hk (obtained from a rotational magnetization model in a uniaxal single domain particle).

Single-domain ferromagnetic cylinder

Abstract: The so called fundamental theorem of W.F. Brown (1988) on spherical particles, which has recently been generalized to prolate spheroids, is extended to right circular finite cylinders. It is rigorously proved that for a cylinder with a radius R, the lowest free-energy state is that of uniform magnetization if R >

Measurement of Magnetization at High Temperatures and the Origin of Thermoremanent Magnetization

Abstract: Recent studies on the measurements of magnetization at high temperatures are reviewed. Use of a second gradient magnetometer is the main advance in instrumentation. Direct observation of how remanent magnetization is acquired and/or lost by changing temperature provides strong evidence about the origin of thermo-remanent magnetization. According to such observation, Neel's single domain theory seems to be correct. Neel's multi domain theory (which is originally a two domain theory, but is frequently applied to grains with many domains), however, cannot explain the behavior of magnetization at high temperatures. The behavior of magnetization in pseudo single domain (psd) grains is strongly dependent on the grain size. It seems that the heterogeneity in the magnetic grains and the screening effect are the main effects which characterize the psd moment.It should be emphasized that at high temperatures, there are still many interesting phenomena which have not been adequately described and/or explained. Some of these interesting phenomena are shown as a guide for future studies.

Induced Susceptibility Anisotropy of Igneous Rocks Caused by Uniaxial Compression

Abstract: The effect of uniaxial compression on the initial susceptibility of a variety of igneous rocks has been studied to determine the dominant factors controlling their response. Hysteresis properties, Curie temperatures, and grain size distributions of the magnetic phases of the rocks have been determined to provide control data.The changes in susceptibility varied from 1 to 10 percent for a stress of 100 bars, with considerable variation in the form of induced anisotropy. In the sample with the coarsest magnetic phases, small decreases in susceptibility (1%) were seen both parallel and perpendicular to the applied stress. The dominance of finer, but still clearly multidomain phases gave rise to larger induced anisotropy (-10%) with the “normal” pattern of an increase perpendicular to stress accompanying a larger decrease in the direction parallel to stress. Samples with pseudo-single domain grain size magnetic phases showed anomalously large increases in the direction perpendicular to stress and only very small decreases in the parallel direction. Some of these samples also showed remarkable increases in susceptibility during loading and unloading. In the finest grain size range, the magnetic particles approached the single domain state and revealed a small (-1%) increase in the perpendicular direction accompanied by a similar decrease in the parallel direction.The dominant characteristic influencing the stress response is the domain state, which is itself strongly dependent upon the grain size. Three types of response are defined. The single domain response consists of an increase in susceptibility in the direction perpendicular to stress and an equal decrease in the direction parallel to stress. The magnetoelastic energy evidently modifies the dominant anisotropy energy against which the magnetization must be rotated by the applied field. In the pseudo-single domain range, wall nucleation appears to produce an isotropic increase in susceptibility. This effect combined with the induced anisotropy characteristic of multidomain material accounts for the observations. In multidomain material, the principal effect seems to be due to loss of wall area parallel to stress, accompanied by some gains in walls perpendicular to stress.

Film-head pulse distoration due to microvariation of domain wall energy

Abstract: Experiments show that the location of spurious peaks on the trailing edges of data pulses is strongly influenced by the application of small DC bias currents to the head coil during readback. A simple model of the head response which includes both magnetization rotation and domain wall motion for the case where domain wall coercivity is comparable to signal fields in the head reproduces many of the features of the observations. Calculations show that fields in pole tips during reading can exceed the wall-motion coercive force of permalloy. It is demonstrated that the resulting domain wall motion could give rise to the spurious signals sometimes seen in thin-film heads. It is proposed that such heads contain domain walls parallel to the signal flux path. The observed oscillations in the spurious response are primarily caused by filter dynamics, not domain wall dynamics. >

Determination of the initial value of the magnetization measurement in pulsed high magnetic fields

Abstract: A sample extraction system was attached to an induction magnetometer which conventionally had been used for measuring the magnetization in pulsed magnetic fields. It became possible to measure the magnetization directly in materials with a remanence such as permanent magnets. The second derivative of magnetization was also deduced to determine the anisotropy field.

A study of magnetization model for particulate media

Abstract: The leakage magnetic field of a single gamma -Fe/sub 2/O/sub 3/ particle is observed by electron holography to be approximately single domain and uniaxial. On the basis of this result, a vector magnetization model is introduced in which curling and rotation in unison modes for a prolate take place. Using this model and the particle size and orientation distributions in gamma -Fe/sub 2/O/sub 3/ particulate media observed by high-resolution scanning electron microscopy, M-H loops and H/sub c/- Omega characteristics of the film are calculated. Moreover, read/write simulations of the isolated pulses are performed using the finite element method. These calculated results agree fairly well with measurements. >

WEAK FIELD MAGNETIZATION AND SUSCEPTIBILITY FLUCTUATION IN Bi2Sr2CaCu2Oy SINGLE CRYSTALS

Abstract: Some magnetization curves of single crystal of Bi2Sr2CaCu2Oy in low magnetic field H ‖ c axis are given. The magnetization loop is getting smaller with the temperature increase and then disappears at temperature even higher than Tc. The experimental measurements of the susceptibility in zero-field limit show that the results can be treated with two-dimensional thermo-fluctuation theory.

Magnetic excitations in monodomain ferromagnetic UTe

Abstract: Neutron inelastic scattering experiments have been found performed with the IN 8 triple-axis spectrometer at the Institut Laue-Langevin, Grenoble, on a single domain crystal of the actinide ferromagnetic UTe. We find that the anisotropy of both the dispersion relation and the damping of the excitations depends on whether the propagation direction is parallel or perpendicular to the moment direction.