Hideo Fujiwara

A New Type of Magnetic Domain Structure in Negative Magnetostriction Ni-Fe Films

Ni-rich Ni-Fe and Ni evaporated polycrystalline films, the thickness of which is larger than a critical value, were found to be composed of stripe domains running parallel to the field previously applied to the films. B-H loops and magnetoresistance effect revealed that the magnetization in each domain points in one sense and deflects from the plane of the film upwards and downwards alternately. This type of domain structure is to be caused by the anisotropy whose easy axis is normal to the plane of the film, the origin of which is attributed to the magnetostrictive effect due to strains or defects in the film. The width of the domain increases with the thickness of the film, but does not depend sensitively on substrate temperatures and compositions. The critical thickness increases with an elevation of substrate temperatures and with decreasing Ni concentration. The stripe domain is no longer observable for the film containing Ni less than 80% where the magnetostriction constant is positive. The relation...

Magnetic properties of multilayered Fe‐Si films

The coercivity and permeability of Fe‐Si films can be improved by laminating several layers with either nonmagnetic (SiO2, Al2O3, Al or Mo) or ferromagnetic (Ni, Fe, Co or 20‐wt. % Fe–Ni) spacers. It is also found that films made with soft magnetic laminations have an advantage over nonmagnetic or hard magnetic ones. Such behavior is concluded to be attributed to the smaller grain size, and pinhole or exchange coupling of multilayered Fe‐Si films by observing domain and grain structures.

Observation of Aharonov-Bohm Effect by Electron Holography

In this experiment, an electronand optical-holographic technique is employed with small toroidal ferromagnets each forming a magnetic-Qux closure. The holographic interferometry proves that a phase difference between two electron beams having passed through the field-free regions agrees well with the fundamental relation known as the Aharonov-Bohm effect. It is also confirmed from the same hologram that Qux leakage from the toroids does not affect the conclusion.

Perpendicular magnetic recording and reproducing thin film head

A perpendicular magnetic recording and reproducing thin film head of a structure excellent in magnetic characteristics and easy of fabrication, wherein a lower magnetic layer disposed on a flat nonmagnetic substrate is used as a main magnetic pole, a first insulator layer is formed on the main magnetic pole, a conductor for a coil and a second insulator layer are disposed on the first insulator layer, and an upper magnetic layer which lies in contact with the lower magnetic layer through the first insulator layer at one end thereof and directly at the other end thereof and which overlies the second insulator layer in a part thereof other than both the ends is disposed and used as an auxiliary magnetic pole.

Observation of recorded magnetization pattern by electron holography

Electron holography was employed for experiments involving a high‐density magnetic recording, in which it was possible to directly observe streams of magnetic flux. The magnetic flux distribution in recorded films, and the maximum packing density in high‐coercivity evaporated cobalt film were investigated. With magnetic longitudinal recording the resultant highest density was 170 000 bits per inch. This experiment has proven that electron holography is useful for the study of magnetic recording.

Simulation of perpendicular recording on Co‐Cr media with a thin Permalloy film‐ferrite composite head

Numerical analyses of thin film head‐medium system for perpendicular recording are performed using a two‐dimensional model. The formulation is based on Poisson’s equation for magnetic vector potential in the head‐medium system. The following conclusions are drawn: (1) Magneto‐motive force needed for producing a sufficient perpendicular field in the medium is about 1/10 that of the SPT (single pole type) head proposed by Iwaski et al. (2) There is an optimum spacing between the magnetic layer and the ferrite of the head that lies 5–20 times the distance between the main pole and the underlayer. (3) The conductor should be placed in the very tip portion of the magnetic layer. (4) Simulation confirms that recording of densities as high as 100 kBPI is possible using a thin film head‐Co‐Cr medium system.

CRITICAL THICKNESS AND PERPENDICULAR ANISOTROPY OF EVAPORATED PERMALLOY FILMS WITH STRIPE DOMAINS

We report that the critical thickness for the appearance of stripe domains in evaporated permalloy films depends sensitively on vacuum pressure during evaporation and also that the perpendicular anisotropy constant can be obtained from the critical thickness rather precisely. It was found that the perpendicular anisotropy increases with increasing pressures and at high pressures the contribution of the magnetostriction effect to the anisotropy can be neglected.

Observation of recorded magnetization patterns by electron holography

Magnetization patterns recorded on Co thin films prepared by oblique incidence vacuum deposition were directly observed by electron holography. Complicated ellipse-like interference fringes were observed along the sawtooth-like walls in the transition regions. Stray magnetic flux was observed in empty space beyond the edge of the film. The following results were obtained from analysis of these interference images. The smaller the product of the remanence and the film thickness, and the higher the coercivity, the narrower is the transition length that determines the limit of the recording density of a medium. It was confirmed that longitudinal magnetic recording of a density of up to 170 kBPI is attainable using Co film 30 nm thick and with coercivity of 112 kA/m. It was quantitatively proven that the intensity of the recorded magnetization in a medium is equal to its remanence when the magnetized area is distinguishable from the transition region.

Patterning effect on easy axis alignment in permalloy thin film

An investigation has been made of the domain configuration in photofabricated Permalloy patterns. In some cases the direction of the easy axis is found to be rotated perpendicular to that initially induced. This change can be explained in terms of uniaxial tension simulated by a two-dimensional finite-element method.

Noise from underlayer of perpendicular magnetic recording medium

Noise from the underlayer is observed with a Mn‐Zn ferrite head and a Co‐Mo‐Zr low coercivity amorphous underlayer. Three kinds of noise are observed, spike noise (s), medium noise (m), and low noise (l). s noise is generated through the domain walls of an underlayer. m noise originates from the interaction between an underlayer and the reproducing head’s residual magnetization. Three effective methods are tested for reducing the noise: (1) increase of coercivity of an underlayer, (2) use of an ac‐erased head, and (3) use of a thin‐film head.