Yoshifumi Sakurai

Magnetic properties and magnetic Kerr rotation of amorphous TbFeCo and TbFeCr films

Abstract The Kerr rotation angle θ k of Tb 21 (Fe 100- X Co X ) 79 increases from 0.18° to 0.36° with increasing Co content X from 0 to 15. On the other hand, θ k of (Tb 21 Fe 79 ) 100- X Cr X reduced with increasing X . The Curie temperature of Tb 21 (Fe 100- X Co X ) 79 and (Tb 21 Fe 79 ) 100- X Cr X rose with increasing Co and Cr concentration.

Preparation and properties of RE-TM amorphous films

Abstract Amorphous magnetic thin films with perpendicular magnetization (GdFe, GdCo, TbFe etc.) are successfully prepared by a sputtering or evaporation technique. The magnetic compensation temperature of these films, which is estimated from M-H curves by Kerr or Hall effect and is a meaningful parameter to study the film properties and devices application, is investigated on preparation condition, temperature and thermal treatment after deposition. Several other studies are involved on electrical properties, magnetic wall microscopic observation and its dynamics. Magneto-optic applications utilizing temperature dependence of coercivity are proposed such as thermomagnetic writing in high density thin film memory.

The Kerr and the Hall Effects in Amorphous Magnetic Films

The temperature dependences of the extraordinary Hall effect (EHE) and the polar Kerr effect (PKE) hysteresis loops are measured in amorphous rare‐earth (RE) transition metal (TM) films. The polarity of each effect corresponds to that of its TM component. The temperature dependence of Hall voltage is similar to that of the Kerr rotation angle, and, in Gd‐Co‐Mo films, it is similar to that of Co sublattice moment calculated by Hasegawas two sublattice model. From these results, both EHE and PKE in RE‐TM films are considered to mainly associate with the TM sublattice moment.

Optical Pattern Processing Utilizing Nematic Liquid Crystals

This paper describes a new type of optical processing based on the dynamic scattering effect in liquid crystals. It is possible to realize a binary spatial filter with nematic liquid crystals and to control the optical modes by voltage signals. A two-dimensional Walsh function is used for extracting properties of the input patterns. The realization of an 8 x 8 Walsh function filter with nematic liquid crystals is demonstrated. The contrast ratio is over 30 to 1. The variation in transparency is within +/-3%. Experimental results show that it is possible to extract the properties of handwritten characters by detecting the intensity of light transmitted through both the input pattern and the liquid crystal filter.

Sm–Co Amorphous Film with Perpendicular Anisotropy

It is very difficult to prepare Sm–Co ferromagnetic film with perpendicular anisotropy, though RE–TM ferrimagnetic films with perpendicular anisotropy are well prepared (RE: rare earth, TM: transition metal). Because of the exceptional magnetic properties of Sm–Co magnetic film as magnetic recording media, we studied to prepare Sm–Co magnetic film with perpendicular magnetization. Films were deposited by a magnetron RF sputtering onto glass substrates (Tsub=80~-100°C) and with a bias voltage (Vb=-60~-80 V). The magnetic hysteresis loops, polar Kerr hysteresis loops and torque curves of this film are characterized by a uniaxial perpendicular anisotropy.

Magneto-optical effect spectra of rare-earth-transition-metal amorphous films

Abstract Some results of the magneto-optical effect spectra of rare-earth-transition-metal amorphous films are presented. These results suggest that the polarity reversal of the Kerr hysteresis loops on the surface of the films after annealing with limited oxidation is sometimes not due to the magnetic origin but may be mainly due to the change of the optical properties of the oxide surface layer.

Temperature Dependence of Anomalous Loop in Double-Layered Amorphous GdCo Film

The magnetic properties of double-layered amorphous GdCo film consisting of films with different compensation temperatures were studied. The theoretical hysteresis loops and their temperature dependence were deduced using the double-layer model. It was confirmed that the magnetic properties of the double-layered amorphous GdCo film agreed well with the prediction by the double-layer model. From the temperature dependence of the double-layered film, it is shown that an apparent compensation temperature exists between the original compensation temperatures in each layer. The appearance of the inverted loop is explained using the double-layer model; this was confirmed by experiments in the double-layered amorphous GdCo film.

Absolute Measurements of the Disintegration Rates of Americium-241 Sources by Using Semiconductor Detectors

Low geometry a counting and α-particle/γ-ray coincidence counting were made to determine the absolute disintegration rate of an 241 Am source. Alpha particles were counted by silicon junction detectors and γ-rays by an Nal(Tl) crystalphotomultiplier system. The half life of the 60 keV level of 237Np was measured to check the effect of the coincidence resolving time in the absolute measurement of the americium source by α-γ coincidence counting; the half life measured was 6.3 × 10-s sec. The mean value of the absolute disintegration rate of a typical 241Am source measured by coincidence counting was 1.696 ×104 dps and the 90% confidence interval for the mean value was [1.679 ×104dps, 1.713×104dps]. Accurate absolute measurements by low geometry a particle counting are very difficult especially for very small semiconductor detectors because of the difficulty of measuring the accurate geometries.

Colour Visualization of Two-Dimensional Distribution of Intracardiac Flow Abnormalities by Multigate Doppler Technique

The detection of flow disturbances in the heart and great vessels by pulsed Doppler echocardiography has great potentials in the noninvasive assessment of valvular and shunt disease (1,2). Recent investigations (3-5) have suggested that the extent or the area of the flow disturbances may reflect the severity of the valvular abnormalities. Current advent of real-time, two-dimensional duplex Doppler echocardiography has provided a more exact localization of the sample volume in the heart and great vessels, and enabled us to evaluate the extent of the flow disturbances very accurately. However, it is sometimes difficult to determine the presence or absence of the flow disturbance from a representation of the audio spectrum, the time interval histogram, since this analysis is easily modified by improper setting and is sensitive to noise and signal amplitude. Although the multifilter soundspectrogram could express all information available in the pulsed Doppler signal, it is also qualitative. Thus, recent interest has focused on Fourier analysis as a possible method of quantitating flow disturbances from Doppler signals (7–10).

Measurement of cubic anisotropy in (111)-oriented garnet films.

This paper describes a simple method for measuring the cubic anisotropy in garnet films. In (111)-oriented garnet films, the magnetization M is rotated from the film normal to the film plane by applying an in-plane field H//. The [111] component Mz of the magnetization M is measured magneto-optically. A plot of MzH// vs. Mz yields an approximately linear relation where the intercept of the line on the MzH// axis changes with the direction of H//, Thus, the cubic anisotropy K1 as well as the uniaxial anisotropy Ku can be estimated from the slope and the intercepts of the extrapolated straight lines for different directions of H//. This method is very simple and may be applied to films whose crystallographic axes in the film plane are unknown. With an adequate choice of the azimuth of the in-plane field, K1 has been estimated with an accuracy of 30%.