Evolution of granular to particulate structure of (001) FePt on amorphous substrates (invited)

Well-aligned (001)-oriented granular or particulate L 1 0 FePt films on amorphous Si O 2 or glass substrates were obtained by depositing atomic-scale Fe ∕ Pt ∕ Si O 2 multilayers followed by various postannealing conditions. After 350 ° C annealing, (001) Fe Pt - Si O 2 granular films were obtained with an average grain size of 5.14 nm , perpendicular coercivity of 7.7 kOe , and squareness of 0.95. The diffusion of Si O 2 to grain boundaries and free surface of FePt accelerated the diffusion of Fe and Pt atoms to form the L 1 0 phase; therefore, low-temperature ordering of FePt was achieved. By further raising the annealing temperature to 700 ° C , isolated particles of aligned (001) single crystals were achieved. The nucleation of voids occurred at low temperatures due to the existence of low-surface-energy Si O 2 , and then an agglomeration process proceeded, leading to a particulate structure. The isolated particles showed a perpendicular coercivity of 60 kOe and squareness of unity.