Thermal Effects in High-Density Recording Media
Magnetic recording is an efficient method to record, store and retrieve vast amounts of digital information. In such a storage system, instability of the stored data or data loss cannot be tolerated. This chapter reviews the effects of thermal excitations on the stability of stored data in magnetic recording media. In order to understand the effect of thermal excitations we first consider energy barriers that prevent the system from spontaneous transitions between different states. In granular magnetic recording media, as used today, these energy barriers are governed by the product of the anisotropy energy density and the grain volume. As head and media parameters are scaled to smaller dimensions, which has been the main path toward achieving higher areal densities, grain volumes are reduced in order to keep the number of grains per bit cell approximately constant. As a result, energy barriers become smaller and thermal excitations may give rise to superparamagnetic effects, which in turn may lead to signal loss over time. In order to avoid superparamagnetic effects and to ensure data stability one typically compensates for the reduction in grain volume by increasing the anisotropy energy density. This approach, however, results in higher write coercivities and is naturally limited by the available write field of the recording head, which traces the thermal stabihty problem in magnetic recording media more to a switching field and writing problem than to an intrinsic media grain stability problem.
KeywordsMagnetization Reversal Areal Density Stability Ratio Switching Field Magnetic Recording Medium
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