Minoru Kume

Magnetic wire and box arrays (invited)

Ferromagnetic wire and box arrays with widths and spacings in the range of 2–0.6 μm were successfully fabricated utilizing high‐resolution electron‐beam lithography and lift‐off techniques. The box arrays possessed a unique magnetic switching mechanism. As the magnetic field decreased, the magnetic coherency between the boxes which are in a row first disappeared. Domain wall motion in each box occurred in the next step. The demagnetizing fields observed in the wire arrays with short spacings were different from those calculated by a model, in which the wires are isolated from each other. Ferromagnetic resonance measurement implied the appearance of interwire dipole‐dipole interaction. Multilayered wire arrays were also prepared to study the magnetoresistive characteristics.

Superlow-Power Readout Characteristics of Photochromic Memory

Readout characteristics have been investigated with a superlow-power readout method in order to solve the problem of information destruction caused by repeated readout operations in photon-mode photochromic memories. For ordinary photochromic diarylethene media, it was possible to read signals of about 105–106 cycles with this method. This method was also applied successfully to wavelength multiplexed recording.

Photochromic reactions of a diarylethene derivative in polymer matrices

Abstract The sensitivity (product of molar extinction coefficient and quantum yield) of 2-(1,2-dimethyl-3-indolyl)-3-(2,4,5-trimethyl-3-thienyl)-maleic anhydride is dependent on its concentration in poly(vinyl butyral) film and on the irradiation wavelength (515 nm and 633 nm). Energy transfer from the open-ring to the closed-ring form is suggested as a possible mechanism for the time dependence of the sensitivity in the polymer film containing high chromophore concentration on irradiation with 515 nm light.

Super-Resolution Disk with a Photochromic Mask Layer

Super-resolution readout for read-only optical disks was demonstrated using a photochromic mask layer. Nonlinear transmittance change, which is desirable for effective super-resolution readout, was achieved using a the photochromic mask layer with an optical density of 0.5. The photochromic super-resolution method is expected to increase the recording density of not only read-only disks, but also magneto-optical and phase change disks.

Optical Density Dependence of Write/Read Characteristics in Photon-Mode Photochromic Memory

When photobleaching reactions are used for writing in a photochromic optical memory, the initial optical density in the recording layer plays an important role in the various write/read characteristics; i.e., secondary harmonics, repeatedly readout characteristics, and crosstalks in a multi-wavelength recording. Better characteristics, that is, lower secondary harmonics, higher readout repeatability and lower nonlinear component of crosstalks, were obtained for media with higher optical density.

Iron nitride thin films with high coercivity and good corrosion resistance

Iron nitride (FeN) thin films prepared by an Ion-assisted Vapor Deposition method have been characterized by magnetic properties and corrosion resistance. Magnetic properties are strongly dependent on the nitrogen concentration and on the minimum incidence angle of deposited iron particles. As a result of corrosion tests, FeN films exhibit superior corrosion resistance to that of Fe film. Consequently, with respect to these points of view, FeN films are suitable for high-density magnetic recording media.

Preparation of High-Coercivity Co–Pt Alloy Films by Target-Facing Type of High-Rate Sputtering

Co1-xPtx (0x0.2) thin films were prepared by using a Target-Facing type of high-rate sputtering (TFTS). The films deposited at lower argon gas pressure PAr(5 mTorr) have only a low coercive force Hc ( 1 kOe) can be obtained at a Pt content of above 11 at%. These films, whose crystallites are oriented randomly, also have a large inplane uniaxial magnetic anistropy constant K1 (\cong2.5×106 erg/cc) and excellent hysteresis loop squareness (S\cong0.87, S*\cong0.98).

Effects of substrate temperature and annealing on the magnetic properties of FeN films

The properties of iron nitride (FeN) thin films for high-density recording media prepared by the ion-assisted vapor deposition method have been studied as a function of substrate temperature during deposition. The coercivity shows a decrease with increasing temperature. This could be caused by the disordered growth of the columns and a decrease in the magnetic separation owing to the migration of the paramagnetic phase. Annealing tests shows that the coercivity decreases greatly following treatment above 250 degrees C, owing to the decrease in the paramagnetic component in the FeN films. It is concluded that the shape anisotropy of the obliquely oriented columnar structure and magnetic separation effects due to the paramagnetic components that segregate along each column are the main origin of the high coercivity of FeN films. >

20 nm domain expansion readout by magnetic amplifying MO system (MAMMOS)

Very small domains are recorded on the MAMMOS disk and they ran be detected using RF readout field. The MO signal amplitude of 20 nm domains can be enhanced to the saturated signal level. For these small domains, the thermal stability problem is investigated. Even if high laser power for readout is irradiated to the small domains, the reproduced signal was maintained. The result indicates that the recording layer of TbFeCo possesses an advantage for paramagnetic limit problem over 100 Gbits/in/sup 2/.

High rate preparation of Co-Cr recording media on continuous film substrates

The properties of Co-Cr thin films prepared by Targets Facing Type of Sputtering method at a high deposition rate up to 1.9 µm/min. have been characterized by vibrating sample magnetometer (VSM) and X-ray diffraction. Magnetic properties of these films are independent of depositon rate, while the HCP