Magneto-optic recording technology (invited)

Abstract

Magneto‐optic recording has great potential as an erasable/rewritable storage technology. Bit densities of 10⁸/cm² are being achieved and improvements can be expected. This paper reviews the status and discusses the most critical issues of the technology. It is shown that the fundamental broadband signal‐to‐noise ratio in existing rare‐earth transition‐metal media is well above 20 dB and therefore adequate to maintain error rates less than 10⁻¹². Substrate imperfections in optical media lead to error rates of 10⁻⁵–10⁻⁶, but even these relatively high raw bit error rates are corrected to 10⁻¹³ by error correction codes and hardware being used in write‐once optical disk storage systems. The stability of magnetic domains recorded into magneto‐optical materials may be explained by a model involving wall energy, demagnetizing fields, applied fields and wall coercivity, and there exist materials which fulfill the requirements necessary to have recorded data remain stable against fields up to 100 Oe and temperatures from 0 to 100 °C. Of more concern is the stability of the amorphous thin films against long‐term annealing. Passivation with optical dielectrics is essential, and preliminary data on some rare‐earth transition‐metal alloys indicate that recorded data would be stable for five years when stored at 50 °C and that the media could withstand in excess of 10¹⁰ write/erase cycles with less that 10% change in minimum stable domain size. It is concluded that magneto‐optic recording technology is a promising high‐density recording technology with a place in the digital storage hierarchies of the future.