Magnetic properties and microstructure of the granular films processed by annealing FePt-based multilayers

To explore the possibility of FePt-based soft/hard nanocomposite magnets, granular films were prepared by annealing Pt/Fe, FePt/Fe, and FePt/Fe₃Pt multilayers. Although a high coercivity of 12 kOe was obtained by annealing the Fe₃Pt/FePt multilayers, only a small remanence was obtained due to random orientation of L1₀ FePt grains. By introducing oxygen during the film deposition, a few nanometer oxide particles were observed within the FePt grains and H_c increased at the expense of M_r. A possible way to achieve a higher value of (BH)_max is discussed based on the relationship between the microstructure and magnetic properties.