Head-to-media spacing losses in perpendicular recording

The perpendicular recording process is essentially demagnetization-free at high bit densities, and the head-to-medium spacing losses become perhaps the most constraining factor in realizing the ultimate capabilities of this technology. In this study we investigated the recording losses resulting from head-to-medium spacing for a double layer madium using a single-pole head and a narrow gap ring head. The spacing was introduced by sputtering Ti overlayers onto the CoCr film in the range of 0.02 microns to 0.18 microns. The recording experiments were performed using a tape deck and a closed tape loop running at low speed. For a spacing d and a wavelength λ, the spacing loss when writing and reading with the single pole head was found to be -99d/λ (dB) for any bit density up to 4Kbpmm (kilo-bits per mm). The spacing losses for the ring head, however, depend on bit density, and are much larger at lower bit densities. In an attempt to separate the writing from the reading spacing losses, we recorded with the single pole head and read back with the ring head. The results of this experiment show that the large spacing losses observed with a ring head at the lower bit densities are primarily incurred during the writing process.