Remanence and Coercivity Measurements of Perpendicular ECC Media

This work reports on advanced remanence and coercivity measurements undertaken on a set of perpendicular exchange-coupled composite (ECC) media, where the demagnetizing field, $H_{D}$, has been properly accounted for. We find that, on correction, the shape of the hysteresis loop, and hence the shape of the remanence curve, changes significantly. More importantly, the value of the measured remanent coercivity, $H_{cr}$, is reduced by between 10 and 15% when the correction for $H_{D}$ is implemented. Measurements of the remanence, $M_{r}$, indicate that the normalized $M_{r}/M_{s}$ varies strongly in the uncorrected case as the thickness of the soft layer increases, whereas for the corrected case, $M_{r}/M_{s}$ is almost constant, around 0.82 $\pm$ 0.03. From the data obtained, we have also been able to determine the reversal processes that take place in both the hard and soft layers. Above a soft layer thickness of $\sim$12 nm, $M_{r}/M_{s}$ becomes dominated by the $H_{D}$. Insight has also been gained into the exchange coupling between the soft and hard layers for a low $M_{s}$ soft layer.