Junko Nakamura

High Storage Density Optical Recording with a Stable Micro Green Second Harmonic Generation Laser Consisting of Nd:YVO4 and KTP

A stable micro second harmonic generation (SHG) laser consisting of a diode- pumped Nd:YVO4 laser doubled by KTiOPO4 achieves 3 times higher storage density than usual on an erasable optical disk.

High-density SHG laser readout with Pt/Co MO disk

To increase the recording bit density of a magneto-optical disk using a shorter-wavelength laser, readout characteristics of disks with Pt/Co multilayered films were investigated by using a 532 nm SHG laser. The experiment using a (lambda) /4 - (lambda) /2 plate differential detection system showed that the disk noise of the Pt/Co disk was caused by a fluctuation of Kerr rotation angle, and that this noise component was reduced by sputter etching the surface of a SiN under-layer. A C/N ratio greater than 40 dB with a 0.45 micrometers domain length was obtained from this noise-suppressed Pt/Co disk.

Anomalous torque curves in PtCo/TbFeCo exchange-coupled bilayer films

Abstract The torque curves, T (α), of PtCo/TbFeCo (RE-dominated) bilayers behave unexpectedly when the applied field H is directed close to the perpendicular ( α =0). The Pt/Co and TbFeCo films separately are characterized by positive effective magnetic uniaxial anisotropy. Consequently we expect T (α)/α to be negative near α = 0. However, we find T (α)/α to be large, positive and approximately constant near α = 0. In this angular region the relaxation of the wall associated with the bilayer exchange coupling drives the Pt/Co and TbFeCo layer magnetizations in opposite directions. On the thin wall model basis, the wall energy, σ w , inferred from the ensuing torque slope is about two and a half times the σ w computed from Kerr loop shifts. The bilayer magnetic energy density, E (α), must be even [ E ( α ) = E (− α )] and in the form of an inverted parabola near α = 0. Physically more realistic distributed wall models must conform to the required symmetry as well as to fit experimental data.

Magneto‐optic disks for high‐density recording with a shorter wavelength laser (abstract)

In order to increase the recording density of the optic disks, it is necessary to shorten the wavelength of the laser beams. Recently, Pt/Co multilayered films have been investigated for the optic recording media using the laser with the wavelength shorter than 600 nm because of the high Kerr rotation. It is, however, difficult to write the magnetic domains with the diameter less than 0.5 μm stably due to the small coercivity and the uniaxial anisotropy field. On the other hand, it is easy to write the domains with the diameter of 0.3 μm on the conventional media of TbFeCo. To use this advantage, the exchange‐coupled double‐layered film of (Pt/Co)/(TbFeCo) has been developed. The disk structure is Al‐alloy/nitride/(Pt/Co)/TbFeCo/nitride/substrate. The multilayered film of Pt/Co has been optimized to write smaller domains and have a higher Kerr rotation for high output signal. Consequently, the thickness is 20 A/5 A, respectively. It has been confirmed that the 0.3 μm φ domains can be written clearly and t...