Showing papers on "Single domain published in 1978"

Properties of Single-Domain, Pseudo-Single-Domain, and Multidomain Magnetite

Abstract: Despite the influence that paleomagnetism has exerted on the earth sciences, our understanding of thermal remanent magnetization (TRM), which is one of the primary sources of paleomagnetic information, is at best fragmentary and incomplete. In this paper we report on experiments studying TRM properties of magnetites whose particle sizes vary from single domain (SD) to pseudo single domain (PSD) to multidomain (MD). TRM stability has been measured by using alternating field (af) demagnetization, hot af demagnetization, low-temperature treatments, thermal demagnetization, and storage tests. Low-temperature treatments are a great aid in helping to determine whether a sample's TRM is carried primarily by SD, PSD, or MD magnetite particles. Thermal demagnetization is relatively insensitive for predicting particle sizes, while af demagnetization remains the best method for reducing the MD contribution to the remanence. Theoretical considerations indicate that the thickness of a domain wall should initially increase with temperature until a critical value is reached, beyond which the thickness decreases. This result is useful in the interpretation of the hot af demagnetization experiments of MD particles whose median destructive alternating field increases with temperature up to some maximum value before decreasing, while the median destructive field of SD and PSD particles decreases monotonically with temperature. Characteristics of the Lowrie-Fuller test (Lowrie and Fuller, 1971) for equidimensional 0.2-μm-sized particles indicate that a critical TRM-inducing field hc exists, where 0.10 < hc < 0.49 Oe; SD-like behavior is exhibited when the inducing field is greater than hc, and MD behavior is exhibited for fields less than hc. This suggests that the critical sizes for transitions of domain structure depend on the intensity of the inducing field. It is argued that the presence of an external field and, similarly, blocking at high temperatures increase the effective size region of SD/PSD remanence and that remanence might be blocked in grains with a nonequilibrium domain configuration. Estimates of critical sizes for transitions between SD, PSD, and MD behavior depend on several factors including grain shape, temperature, type of remanence given to the sample, mineralogy, and intensity of the field used to induce the remanence.

Characteristics of cobalt adsorbed iron oxide tapes

Abstract: The new magnetic material, "cobalt adsorbed" iron oxide, is an acicular single domain particle developed for high density magnetic recording media. The several magnetic instabilities of conventional cobalt doped or modified iron oxide are improved in this material. The structure of this material is quite different from the others. Generally, the particle for magnetic recording media is uniform in its structure from the surface to the inner part but this is a heterogeneous one, i.e, the inner part is pure iron oxide and the surface part is a high cobalt content structure formed by adsorbed cobalt ion. The surface anisotropy due to the adsorbed cobalt ion is in the order of 106erg/cm3. This surface anisotropy is uniaxial and its direction coinsides with that of the shape anisotropy of the acicular particle. The temperature coefficient of coercivity is as small as that of pure gamma ferric oxide. The new magnetic recording tapes are developed using this cobalt adsorbed iron oxide particles for both the home video tape and the audio cassette tape used in the high bias position. The home video tape is superior in color S/N and maximum output level than conventional one. The audio cassette tape is superior in sensitivity, in maximum output level, and in frequency response at high input level than conventional tapes.

Charged wall behavior in 1-&#181;m bubble implanted structures

Abstract: The domain wall pattern around a non-implanted disk and its coupling with an underlying 1-μm bubble are revealed by using colloid technique with Ferrofluid. The complex domain patterns are interpreted graphically from a three-vertex critical curve, similar to the process in uniaxial permalloy films by using the Stoner-Wohlfarth's four-vertex critical curve. The critical curve is also used to explain the charged wall's whip and flip motions during magnetization reversal around the disk.

Measurements on single magnetic particles

Abstract: A method is described for measuring the properties of single acicular magnetic particles, of about 1 μm in length. A dilute suspension was made of, for example, particles of γFe 2 O 2 in a viscous liquid, and an individual particle viewed with the microscope. The particle, initially at remanence, was aligned by a steady field of a few Oersted. With this field still present, an opposing pulse field was then applied. If this was larger than the remanent coercive force, H R , the particle subsequently rotated (in the steady field) by 180°. Thus by varying the pulse field H R was determined. An extension of the method permitted the determination of the remanent loop, and examples are shown for ∼ 1 μm long particles of γFe 2 O 3 and CrO 2 , H R being approximately 430 Oe and 700 Oe respectively.

Bloch walls correlation and magnetic loss in ferromagnets

Abstract: A new approach to the problem of power loss calculation in ferromagnets is provided, which takes into account the effect of the irreversible jumps of the Bloch walls during magnetization. The magnetization process of the material under cyclical conditions is treated as a random function of time and separated into two components: a) a periodic component which gives rise to a line spectrum and is related to the classical dynamic loss; b) a random component which has a continuous power spectrum and which is responsible for both the total static loss and the anomalous dynamic loss. Bloch walls correlation effects are discussed in relation to the change of this last component and its related losses under different physical conditions.

Bound magnetostatic waves controlled by field gradients in YIG single crystals and epitaxial films

Abstract: By appropriately designing internal magnetic field profiles within thin crystals or films of yttrium iron garnet, one should be able to create apparent "surfaces" or "tracks" of magnetic discontinuity. Magnetostatic waves bound or guided by such gradients would follow appropriate propagation paths with controlled energy velocity. If the mode amplitudes are small at the edges and corners of the sample, surface scattering is largely prevented. Consequently, the Q of the resonance should be governed primarily by the intrinsic linewidth of the bulk crystal together with normal circuit loading considerations. We here develop a general theory applicable to the two-dimensional magnetostatic modes of a single domain thin ferrite circular disk when the dc magnetic field is normal to the plane of the disk and varies radially. We then restrict the treatment to normalized z-directed magnetic fields of the form H z (r)/M = A+Br2nwhere A and B are constants, n is a positive integer and M is the saturation magnetization of the ferrite (assumed uniform). For simplicity, magnetic anisotropy and exchange effects are ignored; dissipation is treated by means of perturbation theory. We find solid theoretical justification for the "track" concept and enumerate frequencies and mode patterns for both gradient-modified boundary modes and gradient-dominated "virtual surface" waves. The important effects from rf fringing fields at the edge of the disk are also considered.

An empirical relation for the saturation velocity in bubble domain garnet materials

Abstract: An empirical relation is given for the saturation velocity of a domain wall in a bubble domain garnet material. The relation is v_{o3} = 0.4\pi\gammaM(A/K_{u})^{1/2} , where V_{o3} is the saturation velocity, γ the gyromagnetic ratio, 4\piM the saturation magnetization, A the exchange constant and K u the uniaxial anisotropy constant. The relation provides a close approximation for a wide range of experimental data. Comparisons between experimental data and theoretical data are made. A possible interpretation of the empirical relation is given.

Magnetocrystalline anisotropy of Sm 1-x Nd x Co 5 alloys

Abstract: Magnetocrystalline anisotropy of the quasibinary Sm 1-x Nd x Co 5 compounds has been studied in detail at temperatures 4.2 - 280 K. Anomalous behaviour of hard direction magnetization curves has been revealed for some alloys at low temperatures. This phenomenon is explained in terms of non-coherent mutual orientations of the sublattice magnetic moments during magnetization process. It is shown that Sucksmith - Thompson method of anisotropy constant determination can give correct results for the studied alloy system.

Influence of Cu-content on the hard magnetic properties of Sm(Co,Cu) 2:17 compounds

Abstract: Sm(Co 1-x Cu x ) 7.8 alloys with 0.07 5 type. Annealing at about 1070 K yielded maximum coercive fields, I H c . The dependence of the coercivity maximum on the Cu-content shows no correlation with the primary magnetic properties of both matrix and precipitate phase. Domain wall energies were determined by means of the magneto-optical Kerr-effect. Coercive fields in bulk samples are obtained when the domain wall energy within the precipitate phase is lower than within the matrix, i.e. there is an attractive interaction between domain wall and precipitates.

Observation of a domain drag effect in amorphous GdCoMo films

Abstract: We report the propagation of magnetic domains in bias-sputtered GdCoMo amorphous films by the domain drag effect. Current was pulsed directly through GdCoMo films which contained stripe domains or an hexagonal array of bubbles or "bubble raft". In both cases, once the current density exceeded a threshold value associated with coercivity, the domains were set in motion at a velocity proportional to current pulse length and density. All experimental observations are consistent with a domain drag effect previously predicted. Characteristic velocities of 2.5 × 10-5cm3/sec-amp per current density were found in films with 1 μm bubbles, in order of magnitude agreement with theory. To our knowledge, this is the first direct experimental demonstration of the theoretically proposed domain drag effect.

Magnetometer 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.

Effect of Uniaxial Stress upon Remanent Magnetization: Stress Cycling and Domain State Dependence

Abstract: Polycrystalline magnetite and rock samples have been subjected to uniaxial compression and stress cycling at room temperature. The changes in the components of remanent magnetization were recorded continuously as a function of stress, and the changes in direction and total intensity of magnetization were inferred. Different types of response were recognized, according to the type of magnetization the sample was carrying, i.e., high field or weak field remanence. The anomalous increase of weak field remanence previously reported, appears partly reversible under stress cycling. However, the changes in the lowest stress range are irreversible and reduce the zero stress magnetization from cycle to cycle. Reversible rotations of the magnetization vector of as much as 180° were observed during each half cycle and were primarily due to changes in the sign of the component of magnetization parallel to compression. An andesite whose magnetic phases are single domain according to hysteresis criteria showed a much smaller effect regardless of the type of magnetization it carried. These results again draw attention to the variety of stress responses and the importance of three component observations in field attempts to detect seismomagnetic precursors.

Domain wall bowing in a FeSi picture frame crystal measured by time-dependent neutron depolarization

Abstract: A new technique is presented to study the shape of a moving domain wall within the volume of a ferromagnetic material, which is based upon time-dependent neutron polarization analysis (3×3 components). A polarized neutron beam passes through the long leg of a single crystal picture frame specimen of 3.5% silicon-iron. A single domain wall travels through the crystal by applying a small block shaped magnetic field on the leg. The polarization of the transmitted neutrons has been analyzed as a function of time. From the measured components increasing wall bowing up to 15 percent has been observed with magnetic fields up to 15 A/m. Beyond that value irregularities due to domain wall breaking have been observed in qualitative agreement with publications by Carr and Bishop. Together with the wall break a relative magnetization reduction of 4.10-3has been observed, which has been attributed to persistent reversed magnetization regions.

Magnetic recording properties of SmCo 5

Abstract: Extremely high coercivity magnetic recording materials are being evaluated for use in secure magnetic documents. Commercially available SmCo 5 particles were milled in a standard binder solution, and coated onto polyester film, to make experimental magnetic recording tapes. Selected magnetic properties and low-bit-density recording characteristics were determined for two SmCo 5 tapes with intrinsic coercivities of 8.9 and 11.3 kOe, and compared with two barium ferrite tapes with coercivities of 4.1 and 5.2 kOe. Both SmCo 5 tapes had too high coercivity for an iron-cobalt core head to record. The SmCo 5 tapes had poorer signal output and alteration resistance than the lower coercivity barium ferrite tapes.

Switching characteristics and domain structures in amorphous toroidal cores

Abstract: The switching characteristics of amorphous toroidal cores were investigated in the range of flux reversal time 10-1∼ 10-6sec and related to the observed behavior of magnetic domains. Samples used were amorphous-ribbon toroidal cores with multi-layer of Fe 40 Ni 40 P 14 B 6 (METGLAS 2826), Fe 78 Si 10 B 12 , Co 74 Si 10 B 16 , Fe 5 CO 70 Si 15 B 10 and Fe 80 P 13 C 7 . The switching time Ts for the flux reversal by constant-current pulse fields was measured for these cores as a function of effective applied field He (=applied field H - coercive force Hc). Domain patterns were observed for single-layer toroidal cores of Fe 40 Ni 40 P 14 B 6 (METGLAS 2826) by the Kerr effect. Both the number of domain walls and the average wall velocity were estimated from observed patterns. The non-linear dependences of Ts on He were explained in terms of the number of domain walls and the average wall velocity based on the observed domain behaviors.

Experimental study of the origin and properties of the defect moment in single domain haematite

Abstract: Summary. The properties of the ‘defect moment’ of two fine-particle synthetic haematite powders were studied at low and room temperatures, in weak and moderate fields with respect to the saturation field of this mineral, and as a function of annealing. Two components were separated, (a) a component of low coercivity due to lattice defects, which disappears at the Morin transition, (b) a component with higher coercivities, due to nonmagnetic impurities, which persists below the Morin transition and is unaffected by annealing.

Distribution of magnetization in elements on chevron detector

Abstract: The magnetization distribution in elements of bubble domain chevron detector is first investigated using the magnetooptical micromagnetometer technique. Distribution curves of in-plane magnetization components are obtained in all types of elements. It is found that the magnetization distribution in elements having interconnections is very different from those having none. It is shown that the magnetization distribution in a chevron which is in row, is not equivalent to the one beyond it. It is shown that the magnetization component on the chevron leg perpendicular to the field is more than zero and amounts to M s at the center of the chevron. Fields are determined in which there are remagnetization and redistribution of magnetization in bubble domain chevron detector.

Magnetic recording medium having light and heavy magnetisation axes - uses first type of magnetic particles and second type of uniformly aligned, strongly anisotropic particles

Abstract: Magnetic recording medium with first type of magnetic particles has second type of uniformly aligned uniaxially strongly anisotropic particles (5). One axis is of light magnetization and a number of axes is of heavy magnetization. The axis of the light magnetization has an intrinsic coercive force of less than 1900 Oersted. Initially the second particle population is magnetized with a field of at least 2500 Oersted in the light magnetization axis. The residual magnetic moment of the particle population is at least 40 per cent. higher than the initial residual magnetic moment after an alternating field for erasing has been introduced in one of the magnetization axes.

Wall state stability of bubbles in uniaxial double-layer LPE films

Abstract: Wall state transitions and stability measurements were performed on a series of double-layer films which contain 2μm bubbles. The film comprises a capping layer with uniaxial anisotropy but low saturation magnetization and a bubble layer with high saturation magnetization. Both types of domain wall states, "0" and "1", are found to be stable over a wide range of in-plane field values and even down to zero field. A theoretical explanation of the domain wall transitions and structure is also given. For bubble lattice devices, the new composite films may remove the in-plane field constraints on device functions imposed by the bubble wall states.

Magnetization, coercivity, and magnetostriction studies of electrodeposited Ni-P Alloys

Abstract: M-H hysteresis curves and magnetostriction have been mea-sured for Ni-P electrodeposited alloys as a function of composition from pure Ni to 16 at. percent P. Saturation magnetization decreases linearly with increasing P content at 77 and 300 K. Intrinsic coercivity also decreases with increasing P content and its variation with compo-sition indicates a change from multidomain to single domain to superparamagnetic behavior. The absolute value of the magnetostriction also decreases with increasing P concen-tration. For films with up to 6 at. percent P, there is a rapid increase in the absolute value of magnetostriction followed by a more gradual rise; this behavior is typical of a film with multidomain grains. Films with more than 6 at. percent P do not show this behavior and instead act as if they consisted of single domain particles.

Specific features of low‐frequency sound attenuation in LiNbO3 poly‐ and single‐domain crystals

Abstract: The internal friction Q−1 in LiNbO3 single-domain and poly-domain crystals is investigated It is found that the Q−1 maximum in the vicinity of 300°C is the supperposition of two peaks Q−1 maxima at −30 and 300°C are discussed in terms of the interaction model between domain boundaries and two types of charged point defects having different mobilities [Russian Text Ignored]

Effect of tensile stress on the magnetic domain structure of Fe and NiFe thin films

Abstract: A systematic study was made on how tensile stress affects the magnetic domain structure of RF‐sputtered Fe and NiFe films. These films have thicknesses of 100 to 500 A and various orientations of the stress axis relative to the magnetization. Stressing was done in the plane of the film and the effect was observed in situ using Lorentz microscopy. When large rotations (i.e., 50° to 90°) of the magnetization are required in response to the applied stress and the domains are large (i.e., ≳10 μm), the magnetization rotates smoothly as the stress is increased. This realignment of the magnetization often creates head‐on domain walls with a concomitant increase of the magnetostatic energy which is partially relieved by a faceting of the walls into a sawtooth geometry. For small domains similar wall faceting results and can extend entirely across a domain, splitting the domain into smaller sections which are then gradually eliminated. Thus, a region consisting of several domains can be transformed to a single dom...

Wall susceptibility of magnetic materials having spherical grains with statistical distribution of diameters

Abstract: The influence of the domain-wall size distribution on the wall component of the initial magnetic susceptibility has been considered. The basic consideration has been carried out on a model of magnetic material composed of spheres. Examples imitating the cases occuring in reality are given. It is inferred that the susceptibility depends strongly on the type and parameters of grain size distribution and on the number of walls inside the grain.

Magnetic properties and noise in cylindrical Permalloy thin-film magnetometers

Abstract: The magnetic properties and low-frequency noise measurements of thin films of Permalloy are described. The films are obtained by electrodeposition. They are polycrystalline and single domain. The noise due to the film is shown to be an increasing function of the dispersion angle α 90 . A model for the noise mechanism taking into account the magnetostatic stray field arising in the grain boundaries and the thermal agitation energy is given. It is in qualitative agreement with the experimental results.

Domain wall dynamics near the compensation point in amorphous magnetic films

Abstract: We have investigated the dynamics of an isolated straight domain wall near the compensation temperature in rare-earth transition metal amorphous magnetic films. Wall velocities up to 3.5 × 104cm/sec are observed for applied field up to 550 Oe. Nonlinear dependence of the wall velocity on drive field is observed. The wall mobility in low drive region is very sensitive to the temperature and/or to the coercive force of the film. In high drive region, remarkable transient behavior, that is, very high instantaneous velocity just after the onset of wall motion and velocity break down are detected. Some films have remarkable orthorhombic anisotropy, and in these films the domain wall velocity depends on the direction of the wall motion with respect to the in-plane easy axis of the film. Change of the wall velocity by Permalloy overlay is also observed.

Domain wall drift due to nucleation during cyclic magnetization

Abstract: A detailed investigation was made, using Kerr effect cinematography, of the domain wall motion during cyclic magnetization in single crystals of a 3% Si-Fe alloy. At low levels of peak magnetic induction and magnetization frequency the midpoint of each slab-like domain remains stationary. With the onset of domain nucleation, at higher inductions and frequencies, as previously observed, the existing domain structure is found to drift to accommodate the new domains. Such drift contributes to additional eddy-current losses during the cycle. These losses can be approximated for simple models of the drift process by making use of eddy current losses associated with a domain structure.