Hirofumi Sukeda

NEW RECORDING METHOD COMBINING THERMO-MAGNETIC WRITING AND FLUX DETECTION

We have developed a new perpendicular thermo-magnetic recording method coupled with magnetic flux detection. The resolution is substantially improved by flux detection. Compared to the latest magneto-optical disk drives, the carrier-to-noise ratio of a reproduced signal is 5 dB higher, and the recording density reaches 8.3 Gbit/inch2. Moreover, this recording method has a good affinity to near-field optics, and it is an effective technique for attaining a higher density beyond the super-paramagnetic limitation in longitudinal magnetic recording.

High Speed Overwritable Magneto-Optic Recording

To achieve high speed overwriting on magneto-optic disks, magnetic field modulation recording using a floating magnetic head has been developed. High reliability for the removable disks can be attributed to the large head-and-disk spacing(2~4µm), and thick coating(5~10µm) on the disk. Characteristics of high speed overwriting were investigated at recording frequencies over 10MHz. No residual pre-recorded signal was observed after overwriting.

Highly efficient probe with a wedge-shaped metallic plate for high density near-field optical recording

The distribution of the optical near-field generated by a probe with a wedge-shaped metallic plate was calculated using a finite difference time domain method. The dependence of the distribution on the size and the material of the metallic plate was calculated, and it was shown that a strong optical near-field was generated at the apex of the metallic plate when the size and the material were optimized so that a surface plasmon was excited in the metallic plate. The influence of the recording medium was also calculated. The resonance wavelength shifted toward a longer wavelength and the decay length of the optical near-field increased when the recording medium was placed near the probe. The spot size calculated on the surface of the recording medium was 30 nm, and the efficiency (defined as the ratio between the power of the optical near-field at the surface of the recording medium and that of the incident light) was about 20% when the spacing between the probe and the recording medium was 10 nm. The near...

Thermally assisted magnetic recording on flux-detectable RE-TM media

We studied a thermally assisted magnetic recording on flux-detectable RE-TM media. This recording scheme has a close affinity with near-field optics such as solid immersion lens (SIL) optics and scanning near-field optical microscope (SNOM)-type optics. The requirements for high-density thermo-magnetic recording and a novel near-field optical head were discussed.

Observation and simulation of 0.3/spl mu/m lenght domain on a high speed rotating magneto-optical disk

The magnetooptical recording characteristics of a 0.2-0.3- mu m-length domain were studied using a magnetic field modulation method. The ultimate goal of the investigation, performed on an extremely high-density magnetooptical disk, was to realize high-speed rotating 5.25-in disks. Through optical observation, it was found that domains of 0.3- mu m length could be recorded separately under the condition of 15.1 m/s linear velocity and 25.2 MHz. However, the domain shape became more irregular with increasing recording power and linear velocity. This could be explained by calculated results showing that the domain wall temperature when the magnetic field is reversed becomes higher as the power or the velocity increases. It was observed that the domain shape of a quadri-layer structure disk with a reflective layer having a higher thermal conductivity, such as Al film, is more irregular. This is explained by the difference in temperature profiles obtained from simulation. >

Exchange-Coupled Magnetic Bilayer Media for Thermomagnetic Writing and Flux Detection

We have newly developed a perpendicular thermomagnetic recording coupled with magnetic flux detection. Conventional magneto-optical thin films with TbFeCo compensation compositions are advantageous for thermomagnetic writing, but insufficient for magnetic flux detection due to low flux density at room temperature. We therefore designed magnetically exchange-coupled bilayer media suitable for flux detection by adding a magnetic layer with high flux density to a conventional TbFeCo magnetic recording layer.

High-Density Magneto-Optic Disk Using Highly Controlled Pit-Edge Recording

High-density pit-edge recording on magneto-optic disks has been achieved with accurate edge control. Storage density of 0.7 µm/bit is obtained by suppressing timing jitters caused by (1) teardrop-shaped magnetic domains and (2) thermal interaction between magnetic domains.

Domain and write–read characteristics for magnetic field modulated magneto‐optical disk with high data transfer rate

Magneto‐optical domain shape and write–read characteristics were investigated in an overwrite scheme using a flying magnetic head. Through domain observation and domain shape numerical simulation on magnetic film, it was found that ‘‘tails’’ of domains must be shortened to increase the carrier‐to‐noise ratio (C/N) at high‐density conditions. To reduce the length of domain tails, isotherms on the magnetic film must be circular. For quick heat flow, we constructed a quadrilayered disk which has a thin metal film. C/N of the disk was about 50 dB at 7.4 MHz (0.75‐μm domain length) with linear velocity 11.3 m/s. Compared with the light power modulation method, the magnetic field modulation method is a more suitable overwrite technique, since the thermal profile is the same for any recording mark length.

Numerical simulation of recorded domain shapes on a rotating magneto‐optical disk

For realizing a very high density magneto‐optical recording such as a domain‐edge recording, the way to control domain shapes and sizes precisely was studied by comparing a numerical simulation with an optical observation of recorded domains on a high‐speed rotating disk. The numerical simulation based on a heat flow analysis was applied to a multilayer structure disk. A teardroplike domain shape was analyzed by this simulation, which causes a timing error of edge detection. This shape could be corrected to a symmetrical shape by using a modulated laser pulse. Moreover, it was found that a distance between two domains was affected by a thermal correlation of two laser pulses. This effect is remarkable when the time interval between two pulses is short.

High density recording for magneto-optical disk drive

To obtain key technique for 1.9 Gbit/in/sup 2/ magneto-optical recording, a new wide groove recording structure and a new edge shift detection method are investigated. Track pitch of 0.85 /spl mu/m is accomplished by the wide groove recording structure. The structure improves signal-to-noise ratio up to +6.5 dB. Recording and playback conditions are precisely controlled with the use of the new edge shift detection method. The detection method separately detects mark edge shifts and inter-symbol interferences by analyzing edge shifts in playback signal. Maximum edge shift of 3% to (1,7) detecting window at bit pitch of 0.40 /spl mu/m is achieved.