The limits to magnetic recording - media considerations

At present longitudinal magnetic recording systems are the basis of all low cost high-density information storage systems. During the recent past the data density stored on rigid disk media which is the higher density format have increased at the rate of 60% per annum compound. However, very recentl y due to the introduction of new advanced GMR spin-valve heads this rate of advance has increased to 100% per annum in laboratory demonstrations. Henc e, it is pertinent at this time to enquire as to where the fundamental phys ical limitations of longitudinal magnetic recording may lie. In this contex t there are two principle areas of interest: the first of these is limitati ons to data rate. These are concerned with the fundamental physics of the m aximum rate at which a magnetic moment may reverse from one direction to th e other. The theoretical calculation of these limits is complex and not wel l understood but the limits of our understanding will be reviewed in this p aper. Secondly, and of principle concern is the limit to the density at whi ch information can be stored in a magnetic thin film, This latter limitatio n is based around the signal to noise ratio and also the question of the st ability of increasingly small written bits. Signal to noise considerations are extremely complex and derive from factors such as the shape of bits and cross-talk between neighbouring bits or even neighbouring tracks. In this article the fundamental origins of noise will be reviewed in terms of the b asic physics that gives rise to variation in transition shapes. Cross-talk and cross-track interference will not be discussed as these are generally a ddressed through issues associated with the resolution of the servo-mechani sm that positions the head above a track and is not associated with the fun damental physics of the medium itself Thermal stability of a bit of informa tion is of critical importance particularly as media is made ever thinner a nd will form a major aspect of the discussion in this work. Finally, possib le material physics solutions to some of these limitations will he presente d in terms of measurable parameters which to some limited degree may be con trolled by process conditions. (C) 1999 Elsevier Science B.V. All rights re served.