The magnetization reversal process is investigated in perpendicular spring magnets of epitaxial L10 FePd/FePt (24 nm) thin films with varying FePd thickness. For thin FePd layers, the reversal is initiated by the nucleation of reversed bubble domains and is then mainly accomplished by the depinning and lateral movement of domain walls. For thick FePd layers, the magnetization reversal is predominantly governed by the nucleation process rather than wall motion, resulting in an increased density of bubble domains at more negative magnetic fields. The switching field is reduced significantly with increasing FePd thickness and exchange springs are formed locally due to a tilted magnetization in the FePd. These results arise from the interplay between differently strong perpendicular magnetic anisotropies in FePd and FePt and from layer dependent structural modifications, which is important for high density magnetic recording media.

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