Origin of open recoil curves in L10-A1 FePt exchange coupled nanocomposite thin film

•L10-A1 FePt nanocomposites thin films of different thickness have been fabricated by DC sputtering.•Hysteresis curve measurements exhibit perfect single phase (L10) like behavior for thicker films.•SFD reveals that the openness of recoil curves is directly linked with the amount of uncoupled soft (A1) phase.•Monte Carlo simulation predicts that the extent of exchange interaction increases with thickness of the film.

Mixed phase FePt systems with intergranular coupling may be looked upon as natural exchange spring systems. The coupling strength between the soft and hard phase in these systems can be analyzed using recoil curves. However, the origin of open recoil curves depicting the breakdown of exchange coupling or anisotropy variation in hard phase is still an ambiguity and requires an in-depth analysis. In order to investigate this, an analysis of the recoil curves for L10–A1 FePt nanocomposite thin films of varying thickness have been performed. The switching field distribution reveals that the maximum of openness of recoil curve is directly proportional to the amount of uncoupled soft phase present in the system. The coupling between the hard and soft phase is also found to increase with the thickness of the film. Monte Carlo simulations on a model three dimensional array of interacting nanomagnetic grains provide further insight into the effect of inter granular exchange interactions between the soft and hard phases.