On remanence loops and recording performance

Abstract

Magnetization transitions in recording media have frequently been modeled by a distribution of the form Mr arctan (x/a), where the transition length ‘‘a’’ is presumably determined by the Mrt/Hc ratio of the medium and the head field gradient. We propose that the remanence loop parameters are more relevant to the magnetic recording process than the hysteresis loop parameters. Measured from the remanence loop in the direction of orientation, the important parameters for recording include the switching field distribution (SFDr), the initial slope of the remanence curve, and, of course, the remanence (Mr) and remanence coercivity (Hr). In this respect, medium perfection is reflected in perfectly rectangular remanence loops. Furthermore, a large angular dependence of Hr (from the easy to the hard axis of the media) is also very desirable in minimizing sidetrack writing and recording demagnetization. This proposal is justified by comparing the hysteresis, remanence, and recording properties of various advanced particulate (Co-modified iron oxide and Ba-ferrite longitudinally oriented media) and metal thin-film media. A rather surprising result was the attainment of superior high density response and a high signal output in BaFe media with extremely small SFDr, even though the half-pulsewidth is not commensurately small because it is masked by the contributions of effective spacing, media thickness, and gap length. These thicker BaFe media provide equivalent recording performance to that of much thinner and higher coercivity metal thin-film media.