Magnetic Reptation and the Exchange-Spring Effect in Composite Perpendicular Recording Media

The switching mechanism in two different types of hard-soft stacked, exchange-coupled composite perpendicular recording media was investigated through studies on magnetic viscosity, hysteresis reptation and reversibility. For the first set of samples, the anisotropy of the soft layer was much smaller and its intergranular exchange much stronger than that of the hard layer. For this set, the viscosity and reptation coefficients correlated with the switchability, as did peak recoil susceptibility. The athermal reversibility, which was obtained from the reptation measurements and is a measure of the reversible moment after subtracting thermal agitation, also correlated with the switchability. This media set exhibited a switching mechanism consistent with the exchange-spring effect in all aspects. For the second set of samples, where the anisotropy of the soft layer was only slightly smaller and its intergranular exchange slightly stronger than that of the hard layer, the media still exhibited improved switchability. However, no clear evidence for the exchange-spring effect could be found either in the viscosity or reptation curves, in the peak recoil susceptibility, or in the athermal reversibility. Thus the observations were consistent with the exchange-spring effect for the first set and not so for the second set.