Nobutake Imamura

Magneto-Optical Recording Characteristics of TbFeCo Media by Magnetic Field Modulation Method

To determine the most suitable composition for a magnetic field modulation recording, we investigated the static and dynamic recording (optical modulation method) characteristics of a TbFeCo film relative to an external magnetic field. It was made clear that the demagnetizing field is the chief determinant of the external magnetic field intensity and that a medium with a compensation temperature between room temperature and about 100°C is suitable for magnetic field modulation recording. AC/N of 50 dB was obtained by modulating the external magnetic field at 500 kHz. An overwriting on the pre-signal was completely realized up to the frequency of 500 kHz.

Magneto-optical recording on amorphous films

The development of amorphous TbFeCo alloy films is summarized and from the dynamic read/write characteristics, TbFeCo films are confirmed to be very useful for digital memory applications. That is, the value of C/N is more than 50 dB and life times of more than 5 years were obtained even in the case of a PMMA substrate disk in ambient-air. From the study of oxidization resistance, it was confirmed that the long life time of this TbFeCo disk may be improved by adding some elements such as Pt, Ti, Al and Cr to TbFeCo. Some typical applications of this magneto-optical disk such as digital audio, digital still video file and digital data memory systems are also shown.

Dynamic read/write characteristics of magneto-optical TbFeCo and DyFeCo disk

Amorphous ternary TbFeCo and DyFeCo alloy films were prepared on PMMA pregrooved disks with a dielectric surface layer by Electron-Beam Evaporation technique. Thermomagnetic recording and readout experiments were carried out on these disks using magneto-optical disk player with a detector of Si-APD. It was found that S/N, proportional to \sqrt{R}\cdot\Theta_{k} , is dependent on the thickness of dielectric layer both theoretically and experimentally, where the optimum thickness exists. The mean value of carrier-to-noise ratio (C/N) of 53 dB (resolution bandwidth 30 KHz) was obtained at 2.048 Mb/s (NRZ), which was 5dB larger than that of the disk without a dielectric layer.

The Effect of Noble Metals on Oxidation Resistance of TbFe

The effect of noble metals (Pt, Au, Ag and Cu) was examined on oxidation resistance and Kerr rotation angle of TbFe. As a result, these elements generally had rather small effect on Kerr rotation angle. And Pt was found to have the most remarkable effect on the suppression of pinholes and the improvement of corrosion resistance within the composition range where Kerr rotation angle did not decrease.

Pt layer thickness dependence of magnetic and structural properties of epitaxial Fe/Pt (001) multilayers

Abstract Magnetic and structural properties of epitaxial Fe/Pt (001) multilayer are investigated using torque magnetometer, vibrating sample magnetometer and four-circle X-ray diffractometer. The interlayer coupling across a Pt layer changes with varying Pt layer thickness. The coupling constant for [Fe(25.2 A)/Pt(19.4 A)]15 (001) multilayer is estimated to be −0.02 erg/cm2. The hysteresis loop shows a spin-flop behavior because the coupling is not large enough compared with the magnetocrystalline anisotropy. Magnetocrystalline anisotropy of Fe layer is lost at the interface. Pt layer at the interface is magnetically polarized. Out-of-plane and in-plane magnetic anisotropies are almost independent of Pt layer thickness.

Amorphous TbFe ultra thin film with reflective Au layer

Abstract The thermomagnetic writing and reading of TbFe thin films with reflective layers were studied. As a result, we found the suitable thickness of SiO-buffer and TbFe layers for low writing laser power and large effective Kerr rotation angle.

Hydrogen-containing SiCN protective films for magneto-optical media

Three types of SiC-SiN film were investigated for protective layers of rare-earth transition-metal thin films. The SiC-SiN films were prepared by RF magnetron sputtering with varying combinations of target and reactive gas: (1) SiC/Ar and N/sub 2/, (2) Si/Ar, N/sub 2/, and CH/sub 4/, and (3) Si/Ar, NH/sub 3/, and CH/sub 4/. The SiC-SiN films of the first and second types were chemically unstable. The films of the third type (SiCH:H) were stable and had good optical properties (transmittance, >90%; refractive index, 1.9-2.1). Deposition rates of SiCN:H films were 1.5 times greater than those of SiN films. Magnetooptical media of polycarbonate substrates using the SiCN:H films had high sensitivity and reliabilities. Optimum recording powers for the media using the SiCN:H films were 1-2 mW lower than for the media with SiN films at linear velocity 4-12 m/s. For the media with SiCN:H films no appreciable changes were observed in values of carrier-to-noise ratio and bit error rate after a 75 degrees C-80% relative humidity aging test for over 1500 h and after a Z/AD test of over 40 cycles. These results can be explained on the assumption that hydrogen and carbon bound to Si and N make the SiCN:H film similar to organic structures with flexibility and hence improve affinities between the film and substrate. >

The thermo-magnetic writing and erasing properties and Kerr rotation angle of amorphous RE-Fe thin films

Abstract The thermo-magnetic writing and erasing properties and magneto-optical read-out properties of amorphous rare earth-iron (RE-Fe) thin films are studied. As a result, it is found that both properties depend on RE composition and that RE-rich film is rather suitable for magneto-optical recording media.

Present and Future of Magneto-Optic Disk

In the past eight years, the C/N value of Magneto-optic (MO) disks increased 5 db/per year and is now 60 db at 1 MHz. This advancement was achieved not only by the optical head improvement but also by the material design. The C/N value depends on the several factors such as disk structure (on groove → on land, Trilayer → Quadrilayer), material (TC, θk, domain structure…). In the present MO-disk, minimum bit length is 0.75 μm and track pitch is 1.6 μm. The bit density, thus obtained 8 × 10 bit/cm, is one order higher than the conventional magnetic hard disk. Data transfer rate of MO-disk, however, is 1 MB/s and is several times lower than that of hard disk. In the coming 10 years, the bit density of MO-disk must be improved 10 times or more to the present density, as hard disks will realize in the past 10 years. Data transfer rate also must be improved from 1 MB/s or more than 3 MB/s in the near future. These themes, however, seem possible to realize using following technologies: One is improvement of laser diode (λ = 800 → 600 →. 400 nm, multi-beam) and the other is improvement of MO material (large θk at shorter λ and lower T C ). From thus obtained results, we can estimate more than 20 times higher density and data rate in the coming 20 years. Other important themes such as media life, high sensitivity, and overwrite technology are discussed.

High Sensitive Magneto-Optical Media with New Types of Protective Film

SiCN:H and SiN:H have been studied for use as protective films of magneto-optical (MO) media. These films were sputter-deposited from an Si target in atmosphere containing hydrogen. Both compounds exhibited substantially improved affinities over conventional nitride compounds used as protective films for the polycarbonate substrate of the MO media. In addition to providing superior protection and Kerr rotation enhancement, SiCN:H and SiN:H films had a distinctive advantage that the use of them as protective films reduced the write laser power of the MO media. This feature satisfies the need of higher sensitive MO media applicable to high speed driving of up to 3600 rpm.