Hiroshi Yasuoka

Study of Co‐Cr films for perpendicular magnetic recording using nuclear magnetic resonance

A 59Co nuclear magnetic resonance measurement and a transmission electron microscope observation are utilized to investigate the compositional distribution of Co‐Cr films with and without heat treatment. The spin‐echo spectra of evaporated films are found to be entirely different from those of Co‐Cr alloy powders. The spectra of films comprise a very complicated hyperfine field distribution and the resonant frequencies are much higher than those of powder samples, implying the existence of various kinds of segregation regions typical of a film. Chrysanthemumlike patterns, which disappear with heat treatment, are also observed for chemically etched films. This disappearance is accompanied by the disappearance of the highest‐frequency resonant line.

High-Speed Overwritable Optical Disk

Direct overwriting is studied for both magneto-optic and phase-changing optical disks. One of the most promising approaches is magnetic field modulation on a magneto-optic disk using a floating magnetic head, providing over 15 Mbps data transfer rate. Another candidate is one-laser-beam overwriting on a high-speed crystallizing material such as InSeT1Co. The present status and future possibilities of these two approaches are presented with other approaches for direct overwriting.

Progress of Phase-Change Single-Beam Overwrite Technology

Studies on relationships between single beam overwrite characteristics and physical and chemical properties of the phase change recording media and their mechanisms are reviewed. Improvements in overwrite characteristics based on these studies, especially improvements in carrier to noise ratio(C/N) and the life of recorded dots by the addition of one of the transition metal elements or Tt are also reported. The maximum C/N was 61dB and the estimated life of the recorded dots is longer than 100 years at 60°C.