Showing papers on "Single domain published in 1982"

Properties of Ba ferrite particles for perpendicular magnetic recording media

Abstract: Fine Ba ferrite particles, suitable for coated perpendicular magnetic recording media, have been prepared. The particles, about 0.08 μm in average diameter, are thin hexagonal platelets with easy magnetization axes normal to their planes. Coercivity H c is controllable in a wide range, without significant reduction in magnetization, by Co and Ti substitution. The measured temperature dependences of H c and σ s showed stable characteristics. Good squareness ratio was obtained from an orientation capability measurement.

Perpendicular magnetization structure of Co-Cr films

Abstract: In a perpendicular recording system, a Co-Cr film as a medium is capable of storing very high density signals. Lorentz microscopy of 1000 kV TEM was used to observe the structure of recorded magnetizations in Co-Cr films having perpendicular anisotropy. A composite medium of a Co-Cr film with a soft magnetic back layer was shown by Lorentz microscopy to have a horseshoe magnetization structure. The stable antiparallel magnetization of transition in the Co-Cr layer determined the head-on magnetization structure of the soft magnetic back layer, which consists of a new straw-rope domain structure. The perpendicular magnetization structure of the Co-Cr film was found to consist of small domains magnetized through the film thickness which correspond to the columnar microstructure of the film. Since the intrinsic hysteresis loop of a Co-Cr film was shown to essentially have an ideal rectangular shape, it can be concluded that the Co-Cr layer of a composite film can be recorded by an ideal magnetizing process with negligible demagnetizing field at the transition.

Characteristics of RF-sputtered CoCr films

Abstract: The magnetization of the CoCr recording medium has been investigated by several methods. First the perpendicular hysteresis loops are analysed in the thickness range from 500 to 20,000 A. This provided evidence that the magnetization process is typefied by domain wall motion. Second the dependence of the coercivity on the film thickness has been determined. The dependence found can be explained if it is assumed, that the coercivity is caused by domain walls, impeded by the crystallite boundaries. Finally stand-still recording experiments have been performed, which confirm that magnetization takes place by the displacement of domain walls. The switching criterion in the writing process is best met by taking the field averaged over the film thickness.

Large stable magnetic domains

Abstract: Large, thin‐film single domain areas have been observed, in the absence of a bias field, in garnets with magnetization perpendicular to the film plane.1,2 The domain stability in the work by Krumme1 was attributed to a combination of low saturation magnetization and a low Curie temperature. Uchishiba2 relates the stability in his double layer system to appropriate anisotropy fields in one layer compared to the magnetization in the other layer. A more complete model for large domain stability in a bias field free environment is given in this work. Three distinct stability regimes are predicted by the model and all have been observed experimentally. Areas 3.5‐cm in diameter have been made into stable single domains. This was achieved in a material showing a zero bias strip width of 4.5 μm. The single domain diameter was, therefore, 7500 times the equilibrium energy domain width. The technique developed and the model have led to a new means for observing magnetic defects. More importantly, it also offers a means for measuring the strength of the defects. Possible applications of the model are also discussed.

The microstructure and magnetic properties of electroplated cobalt film for perpendicular magnetic recording

Abstract: In this work, the results of a systematic study of the correlation between the microstructure and magnetic hysteretic properties of electroplated Co films [1] are reported. Based on this study, the origin of the perpendicular easy magnetization in the film is confirmed to be associated with the combined effects of crytalline and shape anisotropy of the Co particles in the film. The variations of the demagnetizing field, H d , and coercivity, H c , which would affect the application of the film in perpendicular magnetic recording are also demonstrated by manipulating the interparticle separation through systematic changes in the plating parameters and the post plating treatments.

Magnetization reversal in sputtered Co-Cr films

Abstract: The magnetic characteristics of a set of r.f. sputtered Co-Cr films of various composition and thickness are examined in order to evaluate their performance for perpendicular recording. The mechanism of the magnetization reversal is discussed on the bases of: i) the shape of the rotational hysteresis loss as a function of the internal rotating field, ii) the value of the rotational hysteresis integral, iii) the dependence of the coercivity H c , and the remanence coercivity H r , on the angle between the easy direction and the field direction. In particular the measurements of rotational hysteresis were performed by monitoring the rate of change of the angular velocity of a top containing the specimen spinning in a magnetic field perpendicular to its axis. The deviation of the experimental behaviour from the ideal models are related to the amount of anomalies in the columnar structure of the film.

Wall clusters and domain structure conversions

Abstract: The significance of wall clusters, which is a new concept in the theory of soft magnetic materials, is experimentally demonstrated in thin Permalloy configurations. The wall cluster is a collection of domain walls that have one intersection line in common. The transformation of the domain structures takes place through a coherent movement of the domain walls. The correlation between the walls is especially dominant at the intersection line of the walls, called the cluster knot. Relations for the mutual positions of the walls in the wall clusters of great practical relevance are derived explicitly and verified experimentally. The domain structure is formed by the concatenation of wall clusters. The clock sense of the rotation over the walls in the clusters determine which walls of two clusters are linked during the formation of the domain structure. The creation of new clusters takes place through the unfolding of the walls of the clusters which originally coincide with the so-called creation line. As is demonstrated fully, the application of these ideas improves the insight into the complex process of domain structure transformations.

A model of anisotropic Alnico magnets for field computation

Abstract: The modeling of an anistropic Alnico magnet for the purpose of field computation involves assigning a value for the material's permeability in the transverse direction. This is generally based upon the preferred direction properties, being all that are easily available. By analyzing the rotation of intrinsic magnetization due to the self-demagnetizing field, it is shown that the common assumptions relating the transverse to the preferred direction are not accurate. Transverse magnetization characteristics are needed, and these are given for Alnico 5, 5-7, and 8 magnets, yielding appropriate permeability values.

Electro-mechanical behaviour of single domain single crystals of bismuth titanate (Bi4Ti3O12)

Abstract: The piezoelectric constantsd 11,d 22 andd 33 for a single domain single crystal of Bi4Ti3O12 have been measured at room temperature using appropriate crystal cuts on a Berlincourtd 33 meter. From the known temperature dependence of the spontaneous polarization, lattice strain and dielectric permittivity, the equivalent piezoelectric constants have been calculated assuming a simple proper ferroelectric in which,P s, is the order parameter. Constants in the plane of the perovskite-like sheets in the Bi4Ti3O12 structure (d 11,d 22) show good agreement with experimental values. The calculated value of the constantd 33 is more than an order of magnitude larger than the experimentally-measured value and gives clear indication of the “indirect” coupling to the strain in the tetrad axial direction and the need for a more sophisticated phenomenology.

Factors affecting the performance of a thin film magnetoresistive vector magnetometer

Abstract: Thin nickel‐iron films with uniaxial anisotropy are vacuum‐deposited onto glass. A bridge‐connected group of conductive meander patterns is formed by photo‐lithography; the current flow in each pattern is aligned at 45° to the anisotropy axis and the magnetoresistors are subjected to bias fields perpendicular to this axis. External fields cause magnetic vector rotation, producing magnetoresistive changes which unbalance the bridge. Poles along the edges of each meander pattern strip generate a demagnetisation field. Its magnitude and direction can be calculated from the effective pole density, which changes with the film’s direction of magnetisation. The field is dependent on the geometry of the conducting strips. Calculation of the equilibrium magnetisation direction is based on the Stoner‐Wohlfarth model, modified by the effects of the demagnetisation field. There is close correlation between theoretical and experimental results, particularly at higher bias levels where most of the film exists as a single domain. Vector magnetometers must have low sensitivity to orthogonal fields. Careful choice of pattern geometry and optimised bias fields in theory allow a zero orthogonal response, a prediction confirmed by experiment. The magnetometer has a linear response and the system noise is less than 1γ per Hz1/2.

Magnetic domain structures and domain walls in iron fine particles

Abstract: In order to estimate the critical particle size lc for a single domain structure, the magnetic energy densities of an iron fine particle are calculated as a function of the particle size for various configurations of magnetization It is assumed in this calculation that in a small particle the energy of a domain wall consists of the exchange, anisotropy, and magnetic stray field energies It is found that lc is 20 nm for a particle with an axial ratio of n = 1, increases with an increase in n, and is 60 nm for a particle with n = 10 The wall energy of a fine particle is found to be much larger than that of bulk material owing to the stray field energy Due to this wall energy, the magnetization configuration is the circular configuration of spins for the particle with a size larger than lc , and it becomes the flux closure configuration by four domains for the particle with a size larger than 900 nm if n = 1 and 600 nm if n = 10

Effect of heat treatment on magnetic properties and morphology of iron particles

Abstract: Acicular iron particles with high coercivity and high saturation magnetization were prepared by reduction of the hematite particles which were obtained by dehydration of the silica‐coated goethite particles in the process of heat treatment in air. Variations in specific surface area, micropore distribution, crystallite size, and magnetic properties with the dehydration temperature were measured. For the iron particles prepared by reduction of the silica‐coated hematite particles obtained by dehydration at 800 °C, a maximum coercivity of 1250 Oe was obtained, and the crystallite size reached the minimum value of 220 A which was close to the critical value of single domain particle. The highly acicular iron particles consisting of the closely packed small crystallites were obtained.

Magnetic domain behaviour of MgFe2O4-CoFe2O4 system

Abstract: Ferrites with the composition Mg1−xCOxFe2O4(0

Effects of finite anisotropy parameter Q in the determination of magnetic bubble material parameters

Abstract: Improved formulas are obtained to provide more accurate determination of magnetic bubble material parameters such as material length (l) and saturation magnetization (M_{s}) based on the measurements of domain stripe width and bubble collapse field. The improvement takes into consideration the effects of finite uniaxial anisotropy parameter (Q) in the formulas. These improved formulas are based on the numerical results obtained from micromagnetic domain calculations of periodic stripes and of an isolated axisymmetric bubble.

Optical study of Bloch walls dynamics during the magnetization process of Fe-Si G.O. laminations under controlled induction waveform

Abstract: By using an optical technique, the dynami cal behaviour of local Bloch wall structures characterized by differently spaced antiparallel domains on the same Fe-Si 3% grain-oriented lamination has been invest igated. A previously developed theory of the magnetic power loss in ferromagnetic laminations allows the correlation of the power spectrum of the time derivative of the optical signal with the local magnetic power loss. From this analysis it can be concluded that on a polycrystalline grain oriented material, magnetized under controlled waveform conditions, the local magnetic power loss is weakly dependent on the domain spacing, particularly when the magnetizing frequency is not very small. This effect, which is mainly due to a balancing effect of eddy currents on the Bloch walls speed is also responsible for the so called curvature anomaly of the loss per cycle vs.frequency plot in such materials.

Thermomagnetic recording methods

Abstract: A thermomagnetic recording method is capable of recording information on a layer (101a) of soft magnetic material which has an axis of easy magnetization normal to the surface of the layer (101a) and in which magnetic bubble domains are generated by application of a bias magnetic field (102, 104). Information is recorded by irradiating the layer with pulses of a focused beam (105) so as to form a magnetic bubble domain having a magnetization opposite to a direction of the bias magnetic field (102, 104).

High-density information magnetoresistive read transducer

Abstract: The magnetoresistive transducer (TMRI) comprising at least one magnetoresistance (MRI) anisotropic magnetic material arranged perpendicular to the running direction information from a medium (SM). The axis (AFAI) of easy magnetization of the magneto being normal to the support, it comprises a single domain thin magnetic layer (ICs) anisotropic normal to the support and the direction of movement strongly magnetically coupled with the magnetoresistance, the easy magnetization axis (AFACI) being normal to the support and in the opposite direction to the axis of easy magnetization of the magneto. Applicable to the reading of magnetic discs and tapes.

Magnetisation reversal of spherical particles containing a single plane domain boundary

Abstract: By locating the boundary positions corresponding to minima in the total particle energy, theoretical magnetisation loops have been deduced for spherical particles divided into two domains by a single plane boundary. The computation of values for the first and second derivatives of the magnetostatic energy has enabled the conditions for the existence of minimum energy states to be quantified and has led to values of 'critical size' for single domain behavior which are about half of those usually quoted. The theoretical predictions are compared with experimental results for SmCo5 particles.

Simulation of skew domain wall bowing in SiFe laminations with asymmetric roll orientation

Abstract: Cyclic motion of 180° domain walls spanning perfect monocrystalline laminations with first-order positive cubic anisotropy (like 3% SiFe) has been simulated using a finite segment technique. Only drive field, eddy field, and surface tension forces on the domain wall were considered. Calculations were made for various crystal orientations over the range between (110) [001]. At intermediate orientations the profile of a rapidly moving domain wall suffers shearing and bowing distortion; this is very different from the symmetric bowing reported in earlier work on the symmetric

Magnetoresistant transducer for reading very high-density data

Abstract: A magnetoresistant transducer is described for reading very high-density a. The magnetoresistant transducer (TMRI) includes at least one magnetoresistor (MRI) of an anisotropic magnetic material placed perpendicular to the direction in which the data of a medium (SM) pass. The axis (AFAI) of easy magnetization of the magnetoresistor is normal to the medium and includes a thin, mono-range or single domain magnetic anisotropic layer (CI) normal to the medium and to the direction in which the data pass. The mono-range or single domain layer is strongly coupled magnetically with the magnetoresistor, and its axis of easy magnetization (AFACI) is normal to the medium and opposite in direction to the axis of easy magnetization of the magnetoresistor. The invention is particularly applicable to the reading of magnetic tapes and disks containing high density data.

Magnetic anisotropy of Ho2Co17 and Ho2Fe17

Abstract: The magnetic anisotropy energy K1, the energy to rotate the magnetization from the easy basal plane to the unique axis, has been measured in Ho2Co17 and Ho2Fe17, both by the magnetization curve and by neutron diffraction. Neutron diffraction studies have been taken to imply a K1 for Ho2Co17 a factor eleven times larger than that measured by magnetization measurements. For Ho2Fe17 the discrepancy may be as large, if one also takes K2 into account. We show that the two sets of measurements are compatible; what has obscured the interpretation of the measurements is the canting of the rare earth and transition metal moments, induced by the field and by the anisotropy torques.

On the pinning of magnetic domain walls by lattice defects in Ni and Ni-alloys

Abstract: The coercive field Hc and the initial magnetic susceptibility χa were used to study the behaviour of the interaction of low and strong defects with magnetic domain walls under low magnetic fields in pure Ni, Ni-3% Cr and Ni-4.5% Cu. The observed independence of the product Hcχa on both the defect density and the strength of interaction was explained in terms of the theoretical prediction made by Hilzinger and Kronmuller. Excess quenched vacancies had no observable effects on the reversible magnetization process in contrast to the case of dislocations. The existence of solute atoms in Ni-alloys would tend to reduce the loading effect of quenched vacancies on magnetic domain walls and low fields were thus required to initiate irreversible magnetization processes.

Method for measuring coercivity in magnetic materials

Abstract: The coercivity of materials that are capable of supporting single wall magnetic domains are measured by an expedient and accurate technique. This technique requires that the material be placed in a static magnetic field having a gradual spatial gradient. Finger shaped domains produced in the material are then modulated by introduction of an AC magnetic field. Coercivity is obtained by measuring the distance the finger domains move due to the AC field.

Magneto-optical modulator

Abstract: In a magnetic layer of a magneto-optical modu-lator consisting of magnetic oxides, location-stable magnetic single domain areas are generated in that the areas of the layer present between the single domain areas to be formed are converted by means of reduction.The reduced areas of the layer show an increased elec-trical conductivity and may be used as electric con-ductor paths.

Magnetic anisotropies of single domain particles as determined by ferromagnetic resonance (FMR)

Abstract: Magnetic structures of single domain particles are influenced sensitively by changes in magnetic anisotropies. FMR experiments enable a determination of both, bulk and surface (or interface) contributions, to anisotropies of thin ferromagnetic films (D?100 monolayers) before and after chemisorption. FMR can also be used to characterize effective magnetic anisotropies of ensembles of particles with statistical orientation of individual anisotropies.