Direct overwrite capability in transition-metal-rich side rare-earth transition amorphous films (abstract)

Abstract

The feasibility of direct overwrite utilizing a demagnetization field was successfully demonstrated by employing transition-metal-rich side Tb-Fe-Co-Cr amorphous films, which is different from previously reported rare-earth-rich side films.1,2 For this purpose, 3.5-in. magneto-optical discs were made in the form SiN/TbFeCoCr/SiN on a pregrooved polycarbonate substrate. To evaluate the capability of direct overwrite, we chose the writing and erasure conditions in such a way that erasure laser power (PE) was set higher than the writing power (PW), applying a constant weak external field (Hex) directed in the direction of erasure. Thermomagnetic writing and erasure at 1.76 MHz were carried out on a disk rotating at 1800 rpm. The carrier-to-noise ratio, C/N, thus obtained was 26 dB in the conditions of PW=8 mW and Hex=-100 Oe. This signal was completely erased by the dc erase procedure (PE=10 mW and Hex=-100 Oe). Furthermore, this signal value was repeatedly obtained by the above writing and erasure sequence. However, when the writing laser power is set higher than the erasure power, the initial readout C/N decreases rapidly within a few write/erasure cycles and cannot be repeatedly reproduced. Observation of the above written bits by using a polarized optical microscope showed no irregular shape domains, but did show a relatively weak light intensity coming from the whole domain area. A more detailed analysis of domain formation will be discussed.