A study on thin-film-media noise by magnetic domain observation

Magnetic domain structures of signal-recorded and reverse-DC-erased thin-metal-film media with different signal-recorded noise characteristics have been observed by a spin-polarized scanning electron microscope to determine the noise-generating mechanism. In noisy media, magnetic domains around 10-μm wide grow at 38 KFCI, and recorded transitions are observed inside them. At the maximum reverse-DC-erase noise condition, which corresponds to the DC demagnetized condition, magnetic domains from 2- to 5-μm wide are observed. In low-noise media, no large, distinct domains are seen for either condition. The squareness (M_r/M_s) of noisy media is 10% higher and the switching field distribution (Δh/H_r) is 40% lower than those of low-noise media. The results indicate that large signal-recorded noise is generated from large irregular magnetic domains that grow through strong exchange coupling between crystallites