Thermal processes may limit the lifetime of stored data and ultimately the achievable areal density in magnetic recording. To quantify this important problem, we have studied a series of state-of-the-art thin film CoPtCr longitudinal recording media samples with thicknesses ranging between 5.5 and 13 nm. Static write/read tester experiments are used to measure the remanent coercivity of these films as a function of the applied magnetic field pulse width, which is varied in the range of nanoseconds to seconds. The data are analyzed in terms of an inverse slope parameter, 1/C, which in the framework of a Neel-Arrhenius model is equivalent to the familiar stability ratio EB/kBT. This ratio is then correlated with signal decay measurements, performed over a time range after writing of 2.8 s to ≈ 1 day. Both measurements are carried out at variable temperatures, T, between 300 and 390 K. The onset of strong signal decay in low density square wave bit patterns occurs when 1/C drops below about 36. © 1999 American Institute of Physics.