Hideki Saga

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.

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.

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 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.

Optimum Timing and Position of Light Irradiation for Thermally Assisted Perpendicular Recording

The optimum timing and position of light irradiation on the medium for thermally assisted perpendicular recording were evaluated in terms of read-write characteristics calculated by micromagnetics simulation. It was shown that the light irradiation timing should be optimized for obtaining the maximum head field and temperature simultaneously. Moreover, the irradiation start time and stop time were determined to obtain the optimum light irradiation timing. It was also shown that the distance between the light-spot center and the head trailing edge should be less than the radius of the light-spot size.

Impact of Multidomain Dots on Write Margin in Bit Patterned Media Recording

Bit-patterned media (BPM) samples were fabricated from hard/soft-stacked [exchange-coupled composite (ECC)] base media with a [Co/Pt]-super-lattice hard layer and a Co soft layer. The write margin of synchronous recording was evaluated using a static tester. The write margin of 50 nm dots with a 120 nm period was confirmed to be 65 nm and a large margin loss almost corresponding to the dot diameter was due to the occurrence of multidomain (MD) dots. Behavior analysis of the average MD dot formation rates within the transition regions beside the write window revealed that recording dots with diameters 30 nm, or smaller, are required to eliminate MD dots. A close association between the MD dot formation rate and the write error rate was confirmed. Therefore, a reduction of the large margin loss arising from the MD dots and a resultant improvement in the write error rate is expected when the recording dots become smaller than 30 nm.

XY-stage driving electron-beam mastering with nanometer-accuracy positioning for high-density optical disk

An XY-stage driving electron beam (EB) mastering system, having an improved EB deflector, was applied to high-density disk mastering with the 40-Gbit/in2 single-carrier independent pit-edge recording/radial-direction partial response (SCIPER/RPR) format. We evaluated the format for pit-edge positioning using an optical filtering technique. A pit-edge positioning accuracy of around 2-nm was obtained and this performed fairly well with the multilevel SCIPER/RPR format. A combination of 40-nm-width pits and nanometer-accuracy positioning has potential in achieving further high-density mastering.

Recording Characteristics of Flux-detectable Magneto-optical Recording Media

We investigated the effect of an additional readout layer in TbFeCo-based bilayer media on the magneto-optical (MO) recording characteristics, by conducting experiments and calculations based on the Huth formula. The bilayer medium with an appropriate readout layer can have equivalent recording characteristics to those of a monolayer one. The designed bilayer medium showed sufficient performance for high-density MO recording, providing a sufficiently strong stray field for magneto-resistive detection. On the other hand, a monolayer medium with large magnetization resulted in poor recording performance due to its self-demagnetizing field. By comparing the recording characteristics, the guidelines for designing the bilayer structure were clarified.

Write Margin Measurement of Bit Patterned Media With 20 nm Dots

Bit-patterned media (BPM) with 20 nm diameter dots and a 72 nm dot period were fabricated from hard/soft-stacked base media with a [Co/Pt]-super-lattice hard layer and a Co soft layer. The write margin of synchronous recording was evaluated using a static tester. All recorded dots were in single domain state, as expected from previous experiments. The write margin was about 50 nm, and there was a total margin loss almost corresponding to the dot diameter. According to an analysis of margin loss factors based on the slope recording model, the margin loss factors for compensating effect of multidomain dots decreased drastically. Therefore it was confirmed that the slope recording model well illustrated the recording process of small dots in single-domain states. The margin loss factor due to the dot position jitter was 17.7 nmp-p and became the dominant loss factor. The loss factor attributable to the switching field distribution also increased rapidly to 11.3 nmp-p and was the second largest loss factor. To secure a sufficient write margin for a robust recording system, suppression of these degradation factors in the BPM fabrication process is required.