Masayuki Katsumoto

Noise characteristics of barium ferrite particulate rigid disks

This paper discusses the relationship between the noise characteristics and magnetic properties of longitudinal barium ferrite (Ba‐F) rigid disks with different switching field distributions (SFD). The magnetomotive force dependencies of reverse dc‐erase (RDC) noise are measured and compared with SFD values. Coated disks with acicular magnetic particles have dips and thin‐film disks peaks in the RDC. In Ba‐F disks, both cases are observed depending on the SFD values, though the depths or heights of the RDC noise are much smaller than those of coated disks with acicular particles or thin‐film disks. Disks with small SFD values have peaks, and disks with large SFD values have dips. In order to find the relationship between noise properties and magnetic properties, interparticle interactions in Ba‐F disks are investigated. Reverse dc remanence Id(H) and ac‐demagnetized isothermal remanence Ir(H) are measured. Both are normalized by the saturation remanence. The deviation from the noninteracting system, ΔM = ...

Interparticle interactions and the switching field distribution of barium ferrite media

A series of barium ferrite disks with a variation in volumetric packing density from 1.5% to 35% were investigated to determine the effect of interparticle interactions on the switching field distribution (SFD) of the media. Kelly et al. (1989) introduced a parameter Delta M(H) to highlight deviations from the theoretical non-interacting assembly. The degree of interparticle interactions were determined from the principal remanence curves and the subsequent calculation of the Delta M(H) parameter. It was found that the SFD of these disks became narrower as the volumetric packing density increased, and that the SFD width strongly correlated with the strength of the interparticle interactions as measured from the Delta M(H) plot. Examination of scanning electron micrographs of these disks revealed that for the low-packing-density disks, separation between the stacks of particles was large and that the separation decreased as the volumetric packing density was increased. It is believed that the properties of the media result not only from the large interparticle interaction arising from particle stacking, but also from the interaction between the stacks. >

Effect of polymer adsorbed layer on magnetic particle dispersion

Experimental and theoretical investigations of dispersion properties of magnetic particles (acicular gamma -Fe/sub 2/O/sub 3/) with an adsorbed epoxy-resin layer are presented. The adsorbed polymer amount was 20-110 mg/g and the adsorbed layer thickness was 6-22 nm, depending on the preparation conditions. Dispersion of gamma -Fe/sub 2/O/sub 3/ particles was evaluated by the sedimentation rate and surface roughness of the coated film. It was clarified that dispersion was improved with increasing adsorption, increasing solvent/epoxy-resin solubility, and decreasing gamma -Fe/sub 2/O/sub 3/ particle size. Interaction energy, consisting of magnetic attraction, van der Waals attraction, and steric repulsion of the adsorbed layer between two cylindrical magnetic particles, was calculated. The interaction energy curves, which vary with the distance between two particles, had primary minimum, maximum, and secondary minimum. The maximum energy and the secondary minimum energy were strongly related to dispersion stability. Experimental results are explained by the energy curve shapes. >

Polymer adsorbed layer on an iron oxide particle surface in iron oxide/epoxy resin/solvent dispersion

Abstract Dispersion of magnetic γ-Fe2O3 particles which have an adsorbed epoxy-resin layer is investigated. γ-Fe2O3 particles which have various amounts of adsorbed polymer are prepared, and some parameters, which characterize the adsorbed layer, are measured. When the amount of adsorbed polymer increases, the thickness of the adsorbed layer also increases, but the polymer concentration of the adsorbed layer is kept constant in accordance with the polymer/solvent solubility. It is found that a low sedimentation rate, i.e., good dispersion stability, is caused by large amounts of the adsorbed polymer.

Polymer adsorption on a magnetic particle in a dispersion system

Abstract A magnetic particle dispersion was prepared by mixing the magnetic γ - Fe 2 O 3 particles or barium-ferrite particles and epoxy resin with solvent. The relationship between the mixing conditions and the adsorbed amount of the epoxy resin on the particle surface was investigated. It became clear that the polymer adsorption occurring during the mixing process required both large mechanical shear and high temperature. The large mechanical shear was necessary to break the coagulation of the particles and high temperature was necessary to cause chemical reaction between the polymer and the particle surface. The adsorbed polymer improved dispersibility of the particles in the dispersion, which was confirmed by transmission electron micrograph, viscosity measurement and surface roughness measurement of the coated films made from the dispersions.

The effect of adsorbed polymer molecular weight on magnetic particle dispersibility

Abstract Dispersibility of acicular magnetic particles which have an adsorbed epoxy resin layer around them is investigated. The relationship between resin molecular weight and adsorbed layer characteristics, e.g., adsorbed resin amount, adsorbed solvent amount, adsorbed layer thickness, is determined. A thick adsorbed layer which contains large amounts of solvent results from the large molecular weight of the epoxy resin. Such a thick adsorbed layer plays an important role in stabilizing dispersion because of its steric repulsion effect. This steric repulsion effect can be estimated by the interaction energy calculation between two particles. The resin molecular weight dependence of dispersibility can also be predicted by the calculation, which supports the experimental results.

Rheological study of magnetic particle dispersion

Abstract The rheological properties of an acicular magnetic particle dispersion, as well as those of a platelet particle dispersion, were studied. The relative viscosity, reduced viscosity and yield value of the dispersion were redefined using the analogy of those of polymer solution to characterize dispersion rheology. The volume fraction of the solid component, which consists of the core particle and the polymer adsorbed layer, is a dominant factor in determining dispersion rheology, independent of the kind of solvent. The magnitude of interparticle interaction, which is indicated by the magnitude of relative viscosity or that of reduced viscosity, is notable when the volume fraction of the solid component is higher than 20%. The yield value rises at a lower volume fraction than do the relative viscosity or the reduced viscosity.

Media noise and interparticle interactions of barium ferrite particulate rigid disks

Abstract This paper discusses the relationship between media noise characteristics and interparticle interactions for a series of longitudinal barium ferrite rigid disks with a variation in volumetric particle packing densities. The magnetomotive force dependences of reverse dc erase noises are measured and compared with interaction field factors. The magnetomotive force dependence of the reverse dc erase noise changes from dip-type to peak-type and the peak height increases with decreasing interaction field factor value, that is with increasing positive interparticle interactions. The coercivity and switching field distribution values decrease with increasing positive interparticle interactions and the volumetric particle packing density. The magnetic interactions in barium ferrite disks consist of two mechanisms, the interparticle positive interactions in stacks of barium ferrite particles, and the negative interactions between the stacks in which the magnetic moments of the barium ferrite platelet particles are aligned in the stack direction.

Interaction energy between magnetic particles in a dispersion system

Abstract The interaction energy between magnetic particles in a dispersion was investigated by calculation. In the calculation of magnetic interaction, the particle was divided into many cells, each of which had an element dipole. The total magnetic interaction was obtained by summing the interactions between these element dipoles. Steric repulsion of an adsorbed polymer layer and van der Waals attraction were also considered. The effects of particle aspect ratio, particle size, the thickness of adsorbed polymer layer, and magnetization on the interaction energy are discussed, based on the results of the calculation. The interaction energy between a particle and a floc is also mentioned.

Method for magnetic orientation of magnetic recording medium using Meissner effect of high Tc superconductor

A method for magnetic orientation of a magnetic recording medium using Meissner effect of a superconductor and a system therefor and a magnetic recording medium produced thereby. The magnetic particles of plate hexagonal barium ferrite in the magnetic coating are allowed to orient in the longitudinal direction thereof so that a magnetic recording medium having a magnetic orientation in such direction with the magnetic particles can be obtained.