Yoshiteru Murakami

New developments in laser-assisted magnetic recording

Recent progress in laser-assisted magnetic recording, which combines optical and magnetic recording technologies, is described in this paper. This study confirms that laser-assisted magnetic recording is a good candidate for high areal density magnetic recording. Improved disk performance was demonstrated in the area of frequency response, media noise, and thermal decay. The improvements in media design include the change in temperature dependence of the recording layer, an increased perpendicular anisotropy, and a thermally efficient layer structure. These improved media properties result in a high linear density and good thermal stability.

Influence of birefringence on the signal quality of magnetooptic disks using polycarbonate substrates

Magnetooptic (MO) disks using polycarbonate (PC) substrates were investigated. Birefringences of the PC disk substrates molded with different methods were measured. Signal qualities for MO disks with the PC disk substrates were also measured and the effect of the birefringence on the signal quality was estimated.

Magnetic super-resolution

Magnetically induced super-resolution (MSR) disks have been proposed to overcome the diffraction limit. This paper reports an MSR disk which has exchange-coupled magnetic double layers. An in-plane magnetization film is used as a readout layer in the magnetic double layers. The MSR disk can be overwritten by a magnetic field modulation recording method. An areal density of 2.2 Gbit/in/sup 2/ was obtained with a currently available optical head having a 680 nm wavelength laser. Besides, the disk had high recorded-data-stability in continuous readout of 5/spl times/10/sup 5/ revolutions with a laser power of 2.5 mW, and it also kept a high signal quality after a continuous erasing test of 2/spl times/10/sup 5/ revolutions with a recording laser power of 6.5 mW.

Improvement of readout resolution with an in-plane magnetization film for a magneto-optical disk

For high density recording of magneto-optical disks, we have developed a new method that improves the apparent optical resolution using a medium that consists of a GdFeCo readout layer and a DyFeCo recording layer. The magnetization of the readout layer is designed to be in-plane at room temperature and to become perpendicularly oriented at high temperatures. Therefore, this medium shows polar Kerr effect only at areas heated up by a readout beam whereas the other areas of the medium are masked by an in-plane magnetization. Using this medium, a small bit at the center of the readout beam spot can be detected without cross talk from the neighborhood. The function of the above high resolution readout method was calculated and confirmed through the study of magneto-optical properties. >

Key Technologies to Realize Magneto-Optical Storage of Over 7 Gbytes in CD-Sized Disk.

Many types of recording technologies have been reported for future magneto-optical (MO) storage. However, they have not been well discussed from the viewpoint of total recording technology including the recording and readout methods, the pick-up technology and the signal processing technology. We propose key technologies for realizing MO storage of over 7 Gbytes in a CD-sized disk using a red laser, and describe the analytical and experimental results pertaining to each key technology.

EVALUATION OF A 120 MM SIZED MAGNETO OPTICAL DISK SYSTEM OF OVER 6 GB CAPACITY

We have studied the feasibility of the 120-mm-sized magneto optical disk system which achieves 6-GB user capacity using an optical pickup with a 640-nm wavelength laser and a 0.6-numerical aperture of the objective lens. We have used three technologies: a laser-pulsed magnetic-field modulation recording, a center-aperture-detection type of magnetically-induced super resolution disk with a 0.6-mm-thick single substrate and partial response equalization with maximum likelihood detection. We have evaluated the system-margins of write power, radial tilt, tracking and focusing offset and have confirmed the feasibility of the linear bit density of 0.235 µm/bit in 0.6-µm track pitches.

Trapping of magnetic domain wall in nickel constriction

The trapping of a magnetic domain wall in a Ni constriction has been observed using magnetic field sweeping-magnetic force microscopy (MFS-MFM). The Ni constriction is composed of wide and narrow tapered parts connected to each other by a constricted area with a 60 nm width. When the MFS-MFM signal, which is sensitive to the perpendicular component of a stray field, is measured around the constricted area, the signal increases at approximately -25 Oe, and is almost constant between approximately -45 and -125 Oe during an applied field swept from 500 to -500 Oe. The constant signal between approximately -45 and -125 Oe is thought to be caused by domain wall trapping around the constricted area. The width of the domain wall has been estimated to be about 260 nm around the constricted area. It is also confirmed that the domain wall spreads more toward the narrow tapered part than the wide tapered part.

Crosstalk canceling for laser-assisted magnetic recording

A promising method of crosstalk canceling is proposed for laser-assisted magnetic recording, which makes it possible to record and read with a narrow track pitch limited to nearly the size of a focused laser spot. In this method, a track pitch narrower than the laser spot size is obtained by utilizing the canceling of the leakage flux from an adjacent track. We achieved a crosstalk of −24 dB or less with a 0.7 μm track pitch in laser-assisted magnetic recording by using a laser spot size of 1.07 μm in diameter and a magnetoresistive head with a track width of 1.4 μm.

Investigation on force transmission of direct-drive thorax unit with four ultrasonic motors for a flapping microaerial vehicle

We fabricated a trial version of a thorax unit with four ultrasonic motors (USMs) to simulate a dragonfly-scale flapping micro aerial vehicle (MAV). Each wing was directly driven by a two-degree-of-freedom (2-DOF) transmission. An in-house tiny standing-wave USM capable of bidirectional rotation, which weighs just 0.13 g, was employed on trial. The transmission of the thorax unit converts the two USM rotations into strokes and flip motions of the wing. By implementing two 70-mm-long wings, we fabricated a prototype of a 4-DOF MAV and tested its performance. In a lift-compensated situation, upward, forward, and backward movements of the MAV were obtained. The flapping angular velocity was discussed based on quasi-static wing aerodynamics and was accountable for the motor power. Although the power of the USM should be improved, the quick wing drivability, adequate power transmission on the thorax unit, and potential of a 0.2 W motor power in a unidirectional-type USM promise the viability of a direct-drive multi-DOF dragonfly-scale MAV. Graphical Abstract

Pinning Effect Induced by Underlayer in TbFeCo Magnetic Recording Media

Pinning effect induced by a grainlike structure on top of a TbFeCo recording layer with an Al or Ag underlayer is investigated. We confirm that the pinning effect depends on the surface structure of the recording layer as well as the underlayer. The Al-underlayered TbFeCo medium shows higher recording density during thermally assisted magnetic recording and higher coercivity than those of the Ag-underlayered one. We can observe that only the Al-underlayered TbFeCo medium has the grainlike structure on top of the TbFeCo recording layer, which reflects well a grainlike structure on the Al underlayers surface. It indicates that the surface profile of not only the underlayer but also the TbFeCo recording layer laminated onto the underlayer is necessary for inducing the strong pinning effect in the TbFeCo magnetic recording media.