Overwrite modulation in Ba-ferrite particulate media

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Abstract
Overwrite modulation (OWM) represents one of the more difficult problems in utilizing Ba-ferrite particulate media for high density recording applications. Any thick particulate medium of high coercivity with preferred perpendicular anisotropy is subject to OWM problems, but Ba-ferrite is even more susceptible in that some of the fundamental properties that contribute to its outstanding recording performance exacerbate its OWM behavior. These properties include a large angular dependence of the remanence coercivity of oriented media, which is reflected in a small transverse field demagnetization and derives from the high uniaxial anisotropy field and the high morphological perfection of the Ba-ferrite platelets. Several possible solutions to the OWM problem are discussed: use separate wide-gap erase heads, wider write gaps, metal-in-gap or other high flux density heads; lower the coercivity; lower the thickness of the media; and longitudinal instead of perpendicular orientation. In addition to these, two other novel solutions are presented: one involves the use of higher than optimum write currents; the other involves the use of thin-film and MR heads (a rather surprising result).