Noise characteristics of Co-Ni obliquely evaporated tape

In Co-Ni obliquely evaporated tape, the magnetic properties and the microstructure are greatly affected by the oxygen gas introduced during the evaporation phase. When the oxygen flow rate is low, the dc-erased noise which is caused by the inhomogeneous structure of the magnetic layer, is greater than the ac-erased noise. The modulation noise level is also high and increases as the carrier frequency increases, as in longitudinal thin-film media having zig-zag transitions. As the oxygen flow rate increases, the signal output level increases to a maximum and the ac-erased, dc-erased, and modulation noise levels decrease. Tape prepared using the optimum oxygen flow rate does not show any increase in the modulation noise as carrier frequency is increased. Analysis of the three noises in the normal and reverse head transport directions made it clear that the ac-erased noise can be affected by the inhomogeneousness of the microstructure in the column, the modulation noise by the irregularity of the magnetic transition region which includes the microstructure, and the dc-erased noise not only by the inhomogeneousness of the microstructure but also by the partial switching caused by the magnetic field of the trailing edge of the Sm-Co magnet. Co-Ni obliquely evaporated tape prepared using the optimum oxygen flow rate is a particlelike medium with a high signal output level and low-noise characteristics.