Super-alignment of magnetic particles on coated discs and its effects on the recording characteristics

Abstract

In order to predict the future trend of the magnetic disc media, we tried to increase the orientation ratio of magnetic particles on γ‐Fe₂O₃ coated discs. By refining the technique of paint‐making, we have realized super‐aligned discs having longitudinal squareness, M_r/M_m of 0.92 and halfwidth of differential M‐H curve, ΔH of 95 Oe with unexpectedly smooth surface. The recording characteristics of the superaligned discs and variously oriented discs were measured using a Mn‐Zn ferrite head. It is found that the reproduced output of highly‐oriented discs is larger than is expected from the increase in M_r and that the half pulsewidth decreases with an increase in M_r/M_m. This suggests the orientation also causes a reduction of magnetization transition length, a. Taking the effect of squareness into consideration, a simple empirical relation, a=ΔH/H_c⋅2tM_r/H_c, was introduced and the obtained data were well explained with this relation. From these results and low noise characteristics of oriented discs, we conclude that the highly‐oriented γ‐FeO₃ coated discs will be suitable for higher recording density, up to 15,000 BPI and 1,000 TPI, having a sufficient S/N ratio.