Double-layer particulate magnetic recording tapes

Double-coated particulate magnetic recording media have been used to optimize recording performance and, in some cases, to reduce cost. The concept involves the simultaneous coating (wet on wet) of a relatively thick (typically 2 to 3 microns) lower coercivity or nonmagnetic underlayer, and a much thinner (a few tenths of a micron) higher coercivity top layer. The author examines and compares some of the most recent and most promising implementations of double-coating technology, which permits the fabrication of very thin, uniform, and very smooth top layers, thus reducing demagnetization and improving short wavelength response and signal-to-noise ratio. In the case of Ba-ferrite top layers, lower coercivity underlayers serve to also boost long wavelength output