A comparison of the thermal stability factors in single layer and exchange-coupled longitudinal media

We have measured the time-dependent remanent coercivity in a series of films to determine the thermal stability of antiferromagnetically exchange coupled multilayers [synthetic ferrimagnetic media (SFM)]. Samples were deposited by dc magnetron sputtering on glass substrates. Antiferromagnetic coupling between the magnetic layers was induced by a 0.7-nm-thick Ru spacer. The measurements were done using an alternating gradient magnetometer and in the series of samples the upper layer thickness was changed. The thermal stability factor (KV/kT) and the intrinsic switching field (H0) were extracted from the fit of the experimental data points to Sharrock’s formula. Single layer samples showed a linear growth of H0 with the magnetic layer thickness with some increase in KV/kT. In contrast, no substantial change in H0 with thickness was observed in the SFM. However, a significant increase in the stability factor of 30% and 44% was observed in SFM samples with effective thicknesses of 7 and 12 nm, respectively, compared to single layer media samples with comparable thicknesses. Data confirm the strong dependence of the stability factor on the properties of the top layer.