On the thermal decay of magnetization in the presence of demagnetizing fields and a soft magnetic layer

The presence of a soft magnetic layer adjacent to a magnetic recording medi um reduces the demagnetization of both perpendicular and longitudinal recor ding media. However, for perpendicular media. there is no reduction in the worst case, DC, demagnetizing field and no lessening of the decay. For long itudinal media, the highest demagnetizing fields occur at high densities. T he soft layer or keeper can reduce these fields significantly and slow the initial decay. The soft underlayer also induces a small anisotropy field th at assists the thermal stability of a perpendicular medium. A similar layer with a longitudinal medium, however, causes a small reduction in thermal s tability, but only at low levels of demagnetizing field. For longitudinal r ecording media the overall effect of the keeper on thermal stability is qui te complicated: the initial decay may be delayed significantly (a factor of ten in time) but the final decay to zero may still proceed more rapidly. ( C) 1999 Elsevier Science B.V. All rights reserved.