In sputtering apparatus using electron-cyclotron-resonance microwave plasma, microwave power was focused to achieve high quahty Co-Cr-Ta/Ti perpendicular magnetic recording disk. Plasma density, deposition rate and quantity of Ar ion irradiation during film deposition were increased with increasing microwave power. A perpendicular magnetic disk with fine grains exhibiting superior magnetic and recording performance was fabricated at high average deposition rate by controlling microwave power, that is, microwave was changed from high power to low power during Co-Cr-Ta film deposition.
Thermal-assisted magnetization time decay for most magnetic recording media exhibits nonlinear behavior against logarithmic time scale, when a long-term(for example 24-hour)measurement is performed. On the basis of measured date for MP and Ba ferrite tapes, the temporal change of magnetization viscosity was approximated by two kinds of distribution function. For Ba ferrite tape, which exhibited the most distinct non-linear magnetization time decay, time constants distributed from 50 to 10^5 sec for the uniform distribution, and the mean-time=5000 sec with standard deviation time=200 sec for the log-normal distribution were obtained.
Since a single pole head for perpendicular double layer media had a very sharp field distribution, it was expected a narrow erase-band width. In this paper, we discussed the dependence of erase-band width on recording densities through the measuring of off-track profiles with a spin-stand. The range of the recording densities during the measurement was from 20 kFRPI to 200 kFRPI. Measured track-widths were almost the same as the mechanical width of the main-pole, and erase-band width around 30 nm was obtained with almost no dependence on recording density and current.
The bit writing process in perpendicular recording media was studied at high frequencies for ring and single pole heads. The effect of varying the writing field strength, the head waveform and the writing frequency were examined. Recording at frequencies of up to 7 Gbit/s appears to be possible in media of less than 200Å thickness. For thicker media S/N ratios are higher if a small amount of exchange coupling is introduced.
We developed the new signal processing system that improves the signal-reproduction performance even under the non-linear distortion(asymmetry), which disturb the precise decording. The system consists of the adaptive equalizer which can detect an accurate error using run length constraint and partial response characteristic, and the viteribi decoder which can control the target levels according to the asymmetry information from the adaptive equalizer. Experimental result with a ROM disk shows that the new techniques improve the error rate characteristics effectively. In this paper, we also describe the new modulation code, which can improve the recording density of an optical disk.