Akira Takahashi

Digital magnetooptic disk drive

A magnetooptical disk drive employing some useful techniques for high performance has been developed for digital file use. A quadrilayer structure with AlN films promises high reliability of the medium as well as enhancement of Kerr rotation. The azimuth of the polarization plane is also increased by the beam splitter, of which Rs (reflectivity of S wave) is larger than Rp (reflectivity of P wave). Parallel control of both actuator and linear motor is used for high tracking accuracy. 4/5 MNRZI modulation is found to be a useful modulation method for the magnetooptical memory system.

High-density laser-assisted magnetic recording on TbFeCo media with an Al underlayer

The effects of an Al underlayer with a nanoscaled rugged structure are studied on the laser-assisted magnetic recording of TbFeCo media. The performance of laser-assisted recording is dramatically improved by employing the Al underlayer. The reproducing signal is observed at the linear density of 450 kilo-flux change per inch. The relationship between the surface morphology and the magnetic properties of TbFeCo media proves that the nanoscaled rugged structure of Al underlayers influences the process of the magnetization reversal; in particular, the coercivity and the exchange interaction are significantly changed in the TbFeCo media. The authors conclude that the nanoscaled rugged structure of the Al underlayer leads to magnetic pinning sites, which impede the motion of a magnetic domain wall, and thereby the laser-assisted recording performance is improved.

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.

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.

The JFT-2M TV Thomson Scattering System

It is the purpose of this report to present a detailed description of the TV Thomson scattering system on the JFT-2M tokamak, produced through the collaboration of the Princeton Plasma Physics Laboratory (PPPL), and the JFT-2M group of the Japan Atomic Energy Research Institute (JAERI).

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.

Magnetic properties of Mn-Zn ferrite thin films fabricated by pulsed laser deposition

We investigated the basic properties of Mn-Zn ferrite thin films fabricated by pulsed laser deposition (PLD) with the aim of controlling their saturation magnetizations (Ms) and electrical resistivities. The Ms and electrical resistivities varied dependent on the substrate temperature during deposition and post-anneal conditions. X-ray diffraction (XRD) measurement revealed the difference is due to the formation of a Mn-Zn ferrite and an Fe2O3 phase, which is attributed to the amount of oxygen in the post anneal atmosphere.