Norifumi Miyamoto

Required conditions for the magnetic domain control of narrow-track read heads to achieve high sensitivity and good stability

We found a relationship between the linearity of the transfer curve in read heads and the instability parameter M/sub x/ that is determined by the magnetization direction in the free layer at the edge region using a Landau-Lifshitz-Gilbert equation. To develop read heads with a. linear transfer curve, which leads to a stable playback signal, M/sub x/ must be larger than 0.9. Using this parameter, we showed the possibility of developing read heads with good stability and high sensitivity. Keeping the magnetic domain control field intensity at the track edge, as well as idealizing its distribution, enabled high sensitivity to be achieved while maintaining good stability.

Optical head with optical beam control using acoustic wave device

An optical head is disclosed, in which a plate-shaped optical wave guide comprises an optical system including a collimator lens, a beam splitter and an objective lens; a laser light source for emitting a laser light in the form of a light beam which is to be impinged on an optical recording medium; and electro-acoustic transducers are disposed between the beam splitter and the objective lens, the transducers being adapted to be driven by the outer electrical signal for producing surface acoustic waves in the optical wave guide, thereby establishing a condensation and rarefaction distribution in refractive index in the optical wave guide which distribution influences the direction of transmission and the degree of focusing of the light beam passing therethrough so that regulation of the tracking and the focal length can be effected without any mechanical movements.

Optical and thermal analyses on multilayered thin films of a phase‐change optical recording disk

A computer simulation method to study a laser‐induced transient temperature profile of a multilayered phase‐change optical recording disk (PCORD) has been developed. The simulation program consists of two parts. One part is an optical analysis program based on the optical characteristic matrix method, and the other is a thermal analysis program based on the finite‐element method. A new estimation method for thermal conductivity of recording films was proposed. The estimated thermal conductivity of the thin‐film recording media was found to be 50% lower than that of the bulk. Reflectivity, absorbance, and temperature values obtained with this simulation method were compared with those measured by a spectrophotometer and an infrared radiation thermometer when the samples were irradiated in an Ar+ laser beam. The accuracy using this simulator was within 8% for reflectivity and absorbance and within 10% for temperature. A method of optimizing the laser‐absorbing layer was studied. With this method simulations...

Overwrite measurement method using pseudorandom sequence

A novel overwrite measurement method with pseudorandom bit sequence (PRBS), random pattern overwrite (ROW) to evaluate the recording performance under the more realistic condition is proposed. A pair of 31-b PRBS are utilized in this overwrite measurement. The ROW is defined as the averaged power over a period of normalized cross-correlation function between the waveforms before and after overwriting. The intrinsic correlation between an initially written pattern and an overwritten pattern, and the effect of the noise are eliminated in the ROW calculation. By using this method, we can effectively evaluate the overwrite characteristics in the condition similar to those in a hard disk drive.

Relationship of Exciting Current to Noise-after-Write of Thin Film Head

The behavior of noise-after-write in thin film heads was studied. The probability of noise-after-write events was decreased by applying a constant amplitude current or a decay amplitude current to the head coil, after shutting off the recording current. A constant-amplitude current was more effective for decreasing noise-after-write than a decay amplitude current. Comparison of the noise pulse of an Ni-Fe head and of a Co-Ta-Zr amorphous head showed that the former had a wider pulse width than the latter.