The contribution of the magnetic medium to phase shift and resolution in magnetic recording

Abstract

Phase shift in a 16-bit 3200 flux-change-per-inch (fci) coded pattern was studied. The pattern was written on thick particulate γ-Fe 2 O 3 tapes, and statistical data were accumulated with a measurement accuracy of about one tenth of one percent. All tapes were unoriented, with remanent moments ranging from 5 to 70 EMU/cm3, coercivities between 200 and 360 Oe, and coating thicknesses between 160 and 700 μin. The position of a peak in time (its phase information) affects recording resolution. To date, most definitions of recording resolution have concerned the properties of isolated pulses such as the half pulsewidth. It is clear that the isolated pulsewidth conveys no information on the timing of the pulse. Resolution, in the context of isolated pulses, is expected to increase as the ratio H_{c}/I_{r} increases. Our results show that phase shift is not minimized, in general, for the medium with maximum H_{c}/I_{r} . In addition, asymmetric phase shifts in a coded pattern were observed, and these cannot be explained by time-independent linear superposition of fundamental pulses. It is suggested that such phase shift studies are a necessary addition to isolated pulsewidth studies if recording resolution and reliability are to be better understood.