Yoshiharu Uchihara

Magnetic properties of multilayered GdDyFeCo thin films

The variation in the magnetic properties of compositionally modulated GdDyFeCo films prepared by two-source magnetron sputtering as a function of the compositional period was investigated. The compositional period was varied by altering the substrate rotation rate; the minimum period was 1.5 AA. Variation of the compositional period caused great changes in the magnetic and magnetooptical properties, while films with a compositional period of 3 AA showed the optimum recording characteristics. Increasing the compositional period caused magnetization of the FeCo layers to increase, and the perpendicular magnetic anisotropy to decrease. The degradation in recording characteristics at 1.5 AA can be mainly attributed to the increasing demagnetization of the field between T/sub comp/ and T/sub c/ brought about by a change in the temperature dependence of saturation magnetization. >

Thickness dependence of magnetic properties in GdDy/FeCo film

For a better understanding of the dynamic characteristics of GdDy/FeCo magnetooptical (MO) disks, the magnetic properties of GdDy/FeCo films with various thicknesses were investigated. The MO layer, whose thickness was varied from 200 AA to 1500 AA, was sandwiched by dielectric SiN layers. Kerr rotation angle decreased as the MO layer was made thinner, while the reflectivity showed little change. T/sub comp/ shifted lower with decreasing thickness, while T/sub c/ was constant. The CNR value saturated above 600 AA thickness, while noise level was less influenced with the thickness. Therefore, the increase in CNR is mainly due to the carrier level and caused by an increase of Kerr rotation angle. The degradation of CNR at lower magnetic fields is also discussed. >

Thermal stability of sputtered GdDyFeCo films with trilayer structure

The thermal stability of GdDyFeCo films with trilayer structure has been studied by annealing in vacuum up to 300/spl deg/C. In GdDyFeCo films sputtered on glass, the coercivity is reduced after annealing, which is thought to be due to a structural relegation caused by annealing. The saturation magnetization tends to increase upon annealing, in particular for rare-earth rich composition because of the increase of effective magnetic moment, making the compensation temperature (Tcomp) shift higher. The films with Tcomp between room temperature and 100/spl deg/C show superior thermal stability, because their magnetic properties, especially Tcomp, change little after annealing. Overwrite repetition tests using magnetic field modulation recording also indicate that the disks with the Tcomp between room temperature and 100/spl deg/C have superior overwrite durability. Small adjustments of the GdDy content seem to be effective in improving the thermal stability of GdDyFeCo films. The best Tcomp of the GdDyFeCo films is between room temperature and 100/spl deg/C, and the optimum Dy:Gd ratio is between 45/55 and 70/30. >

Examination of the read/write characteristics of an mo signal with a wobbled groove clock

We manufactured a high-frequency wobbled groove disk, and examined reading/writing a magneto-optical signal by using a clock generated from the wobbled groove. We also measured clock jitter and bit error rate. The results of this were clock jitter of under 2.5 ns, and a bit error rate almost equal to that of a self-clock. This wobbled groove clock method is therefore effective for higher density recording.

Life estimation based on statistics for single-sided Magneto-Optical disks with GdDyFeCo film

We have developed single-sided Magneto-Optical (MO) disks with GdDyFeCo film, which is suitable for magnetic field modulation method at low constant velocities. The reliability of our MO disk with a simple structure (polycarbonate/ SiN/ GdDyFeCo/ SiN/ UV resin) was examined with accelerated tests. After aging more than 10,000 hours at 65°C 85% RH, carrier to noise ratio was scarcely lowered, while the value of Block Error Rate increased because of extra noise which was produced by local defects. From the statistical analysis and Arrhenius plot, the lifetime of 95% of our MO disks were estimated to be more than 50 years at an office environment.