Direct overwriting capability in TM-rich side rare-earth transition metal amorphous films

The feasibility of a new method for direct overwrite with a power-modulated laser beam under a constant external bias field Hex fixed in the same direction as an initializing field Hinit was demonstrated by means of a dynamic disk tester. TbFeCoCr amorphous films with compensation temperature (Tcomp) far below room temperature were employed, but coercivity falls below 200 Oe at 200°C, while the saturation magnetization remains high. We found that written pits are formed by a demagnetization field Hd in the region of a weak Hex, whereas for a stronger Hex they are formed by a effective external field H eff(=Hex-Hd) fixed in the same direction as Hinit. By using a power modulation between 9 and 5 mW under a constant field of -100 Oe, we were able to demonstrate direct overwrite, although the readout carrier-to-noise ratio was low (18 dB).