Magnetic properties of dilute FePt:C nanocluster films

Abstract

Nanocluster-assembled dilute (FePt)xC100−x films with 30⩾x⩾5 (x denotes volume fraction) were produced using a gas-aggregation technique. FePt clusters with an average size of about 4.0nm (with standard deviation σ∕d=0.09) were embedded in high volume fraction of carbon matrix, which is used to isolate the FePt clusters. Postdeposition annealing was used to realize the high-anisotropy L10 phase. Single-crystal features of well-isolated clusters were observed by transmission electron microscope (TEM) in annealed dilute films. The coercivity of the films annealed at 700°C for 5min was a few hundred Oersteds at room temperature, while a coercivity about 4kOe was observed at low temperature 10K for x=5, indicating partial ordering of the clusters. The coercivity strongly depends on annealing temperature and annealing time, and increases with decreasing FePt volume fraction. For a dilute FePt cluster film with x=5 annealed at 700°C for 60min, a room-temperature coercivity of about 30kOe and low-temperature (10K) coercivity of about 40kOe were obtained, which imply an anisotropy field of 83kOe, assuming the clusters are noninteractive. The results are discussed by comparing with simulations for Stoner–Wohlfarth particles.