Sumio Kuroda

Optimized structure of sputtered garnet disks

The optimum structure of the sputtered garnet magnetooptical disk was investigated by numerical calculations and experiments. From the Faraday rotation, Faraday ellipticity, refractive index, and extinction coefficient, the authors determined the dielectric tensor elements of a sputtered garnet film. Using these values, they calculated the thickness dependence of the magnetooptical rotation angle, the reflectivity, and the reproduced signal amplitude of the disk with a reflecting layer. These results were then compared with measurements. The optimum garnet thickness and reflector material for a sputtered garnet disk were found. The optimum structure has a carrier/noise ratio of 60 dB at a carrier frequency of 0.6 MHz and possesses good recording sensitivity. >

Ce‐substituted garnet media for magneto‐optic recording

The magnetic and magneto‐optical properties of crystallized as‐deposited Ce‐substituted sputtered garnet films were measured as a function of temperature. The films were found to exhibit large Faraday rotation and high coercivity at room temperature. The small grain size and high squareness ratios of these films suggests that this media holds promise as a potential magneto‐optical recording media candidate for use at laser diode wavelengths. Furthermore, it was found that depending upon the value of the sputtering system background pressure prior to film deposition the compensation temperature of these films varied from below room temperature to the Curie point. The temperature dependence of magnetization of these two types of films was found to be very different and ESCA analysis was performed in order to ascertain the origin of these differences.

Sputtered garnet media for magneto-optic data storage

Abstract In situ crystallized Bi,Ga:DyIG and Ce,Ga:DyIG films were deposited on GGG substrates by rf sputtering. The films had single-crystal-like columnar structure, which resulted in low media noise. The films showed square hysteresis loops with large coercivity, the perpendicular anisotropy being ascribed to the large negative magnetostriction of DyIG. The compensation temperature of Ce,Ga:DyIG films changed drastically depending on residual oxygen in the sputtering chamber, and this unique phenomenon was attributed to the site preference of Ga. Furthermore, it was found that the main contribution of Faraday rotation in the Ce-substituted samples was due to Fe in the tetrahedral sites. Dynamic recording was performed using an Ar ion laser, with CNRs of 57 and 48 dB being obtained for Bi,Ga:DyIG and Ce,Ga:DyIG, respectively. The problem of write noise still remains for Ce,Ga:DyIG.

Potential of Bi-substituted sputtered garnet media for high density recording using shorter wavelength lasers

Dynamic recording using Bi-substituted sputtered garnet media on a GGG (Gd/sub 3/Ga/sub 5/O/sub 12/) substrate was performed using several wavelengths of an Ar ion laser. Good writing sensitivity and high carrier-to-noise ratios (CNRs) were obtained in the blue region of the spectrum, indicating that a SHG (second harmonic generation) laser could be adopted as the light source for ultrahigh-density recording. A 785-nm laser-diode tracking servo was reliably performed for pregrooved substrates, producing a CNR of 48 dB. Overwrite experiments using magnetic field modulation were also performed. A CNR of 48 dB was obtained and complete erasure was confirmed. >

Overwrite on Sputtered Garnet Media Using Magnetic Field Modulation

Both a pregroove and aftergroove were formed in a garnet medium on a GGG substrate, and a reliable 785-nm laser diode tracking servo produced. Magnetic field modulation recording for the pregrooved media produced a carrier to noise ratio (CNR) of 48 dB, and overwriting gave complete erasure. Writing was impossible in the off-track zone of the aftergrooved media, which we believe will be useful in improving the overwrite power margin. There is a problem of deterioration of coercivity, caused by wet etching during fabrication of the aftergroove, which remains to be solved.

A magnetic recording media with locally enhanced coercive force

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High-density magneto-optic disk and method of manufacturing the same

%nsiq recordings with a recording density of over 20 Gbit/inch2, servo signal patterns can no longer be written with conventional STW (Servo Track Writer) because of the narrow track pitch in these media, which is less than 0.7 ,urn, or one quarter as wide as current track pitches. A discrete magnetic recording media that doesn’t require STW would solve this problem. There have mainly been proposed two discrete media with this feature: the first of these is PERM, or Pre-Embossed Rigid Magnetic recording media, which contains concave and convex surface structures [I], the other one is ESPAR, or Embedded Servo PAttern under Recording Layer, which has an unstructured surface [ Z ] . Embedded type discrete magnetic recording media such as ESPAR provide strong advantages for proximate recording, since embedded media provides for more stable head operation compared to embossed media. In this work, we propose an embedded-type discrete media that uses a coercive force enhancement layer.