Exchange coupling in FePt‐FePt 3 nanocomposite films

In this study, the structural and magnetic properties of exchange coupled nanocomposite FePt‐FePt 3 films were investigated. X‐ray diffraction and transmission electron microscopy results showed that after rapid thermal annealing (600 °C for 6 minutes), a phase transformation from [Pt+Fe] into composite FePt‐FePt 3 phases was obtained. Annealing created an ordered FePt phase that resulted in a large room temperature coercivity (H c ∼ 3200 Oe) compared to the as‐deposited film (H c ∼ 20 Oe). While no exchange bias field (H ex ∼ 0 Oe) was measured at room temperature, the annealed sample showed significant H ex ∼ ‐500 Oe at lower temperatures (150 K ≤ T ≤ 250 K), indicative of exchange coupling between FePt and FePt 3 . The high blocking temperature (∼250 K) indicates FePt 3 exhibits an enhanced Néel temperature. Further increasing the annealing temperature to 700 °C resulted in a reduction of H ex which is attributed to the transformation of FePt 3 into the FePt phase at this higher annealing temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)