Harukazu Miyamoto

Nanosize fabrication using etching of phase-change recording films

An etching technique called phase-change etching was developed. In this technique, only crystalline regions in a phase-change recording film are selectively etched by an alkaline solution, and amorphous regions remain on the sample surface, which means that a phase-change recording film can be used as a resist for pattern formation. By combination of this technique and phase-change recording, fabrication of the dot pattern with a size of about 1∕10 of the fabricating spot was demonstrated. This result indicates the possibility of nanosize fabrication using the phase-change etching technique.

Integrated head design using a nanobeak antenna for thermally assisted magnetic recording.

We propose a near-field optical transducer using a triangular antenna and a thin film structure (wing) to efficiently generate an optical near-field near a magnetic head. A finite-difference time-domain calculation showed that the near-field was efficiently generated at the apex of the antenna when the dimensions of the wing were optimized for efficient delivery of the surface plasmon excited on the wing to the antenna. The calculated light utilization efficiency (ratio between the absorbed power in the recording medium and the input power) was 8%. The temperature distribution on the medium, magnetic field distribution, and magnetization pattern were calculated; the proposed recording head may be capable of an areal recording density of 2.5 Tb/in.(2).

Mechanism of microwave assisted magnetic switching

The characteristic of microwave assisted switching for an isolated grain was investigated using the Landau–Lifshitz–Gilbert simulation. It was found that anticlockwise and clockwise polarized fields assist magnetization to switch and to reswitch, respectively. Using larger linear polarized field, sufficient switching is not obtained. It was confirmed the magnetic resonance effect on the reduction in the switching field. It was also found that a large assist effect and a narrowing transition effect were achieved in exchange coupled subgrains.

Effect of Elliptical High-Frequency Field on Microwave-Assisted Magnetic Switching

The characteristic of microwave-assisted switching for an isolated particle was investigated using the Landau Lifshitz Gilbert simulation. 1) An effective component of high-frequency (HF) field is one perpendicular to the magnetization, which is in the direction of the effective field under a write field. 2) The anti-clockwise polarized component should be increased in a practical field generation layer (FGL) to obtain larger assist effect. 3) It is necessary to use an elliptically polarized field and to design a microwave-assisted magnetic recording head with FGL with consideration about the direction and the efficiency of the HF field.

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.

Sub-Terabyte-Data-Capacity Optical Discs Realized by Three-Dimensional Pit Selection

To realize optical discs with the sub-terabyte data capacity, we propose the three-dimensional pit selection (3DPS) method where a single data pit to be read out in a multi-layer disc is selected three-dimensionally to obtain super-resolution in the disc plane and to reduce layer cross-talk. To examine the feasibility of this method, the phase-change pit capsule method was tested where the data pits consist of a phase-change material which melts during readout. The super-resolution effect was observed for both layers of a dual-layer disc. It was shown that a quadric-layer disc can be designed because of the high transmittance of each layer. Thus, 3DPS is considered to have the potential for a data capacity of hundreds of gigabytes with a conventional optical system.

Amplification of Optical Disk Readout Signals by Homodyne Detection

We experimentally demonstrated the amplification of optical disk readout signals by homodyne detection. This technique uses optical interference to amplify the signals. We further applied phase-diversity detection to reliably obtain the amplified readout signal. The optical system was carefully designed so that a sufficiently amplified readout signal can be obtained. In particular, we applied a corner cube prism as a reflection mirror to achieve sufficient stability of the interferometric optical system. We experimentally demonstrated a 3.6 times amplification of a Blu-ray Disc readout signal. The estimated signal-to-noise ratio (SNR) improvement for an assumed eight-layer optical disk readout signals by applying homodyne detection on the basis of the observed amplification was +7.9 dB, which significantly enables reliable readout of recorded signals. The present technique will be essential for the real commercialization of next-generation multilayer optical disk because of its outstanding ability of SNR improvement.

Effective Write Field for Microwave Assisted Magnetic Recording

The effective write field of microwave assisted magnetic recording (MAMR) was investigated using the Landau Lifshitz Gilbert (LLG) simulation and an analytical method. An effective component of high frequency (HF) field was obtained by considering the angle between the magnetization of recording media and the HF field generated from field generation layer (FGL). An analytical method to obtain the effective write field was proposed by using the switching properties of the recording medium graphically. The obtained effective write field has shown that the value of the maximal effective field gradient of 1850 Oe/nm is three times larger than that for Stoner-Wohlfarth effective write field.

2 GB/130 mm Capacity Direct-Overwrite Magneto-Optical Disk

Precise mark-edge recording on a high signal-to-noise ratio (S/N) exchange-coupled direct overwrite magneto-optical (MO) disk provides 2 GB capacity on a 130 mm disk with a sufficient edge jitter margin. Write compensation technology was proven to be effective for both non- and direct-overwrite MO disks.

Readout-signal amplification by homodyne detection scheme

Optical signal amplification by a homodyne detection scheme is proposed and experimentally demonstrated. We estimated that this scheme improved the signal-to-noise ratio of an 8-layer 3x read-speed Blu-ray Disc (BD) by more than 20 dB.