A simple high frequency characterization technique extended from DC disk erasure is presented to measure the write field degradation for frequencies up to 500 Mfc/s (250 MHz) on plated NiFe and sputtered laminated FeN heads. The results show that eddy currents appear to be the main cause for high frequency write field degradation. Overwrite recording measurements, which may be used to approximate the non-linear write effects, also indicate that FeN heads, despite low efficiency, may be adequate for writing up to 100 MHz on a disk with a coercivity of 2500 Oe. This disk is capable of supporting 5-10 Gb/in/sup 2/ densities.
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