Magneto-optical recording of sputtered garnet films using laser diode

Abstract

Sputtered garnet film is so transparent in the near-infrared region that recording using a laser diode was thought to be impossible. However, we have found that it is possible if Cr is applied to a thin garnet film. We investigated the sensitivity for static recording. The optical absorption of Cr film is 60% in the 0.8 μm wavelength range, and temperature elevation ocurrs easily. Recording becomes possible through the heat transfer from the Cr to the garnet film. The sensitivity depends mainly on the thickness of the Cr and garnet films. The optical absorption of the garnet film makes little contribution to the sensitivity. Recording needs only 6mW at a pulse width of 0.15 μs for a 0.1 μm thick garnet film by applying a bias field of 150 Oe. This sensitivity is considered to be sufficient for an optical disk mediun. Furthermore, dynamic recording was carried out using a 5-inch glass disk. We obtained a rather low C/N value of 30 dB. The reason for this low C/N value is due to both the irregular bit shape and the medium noise, resulting from the poor morphology of garnet film.