Effect of Film Thickness on Magnetic Properties of FePt Thin Films Deposited on Amorphous ${\rm SiO}_{2}$ Substrate Directly

FePt thin films with different thicknesses (2.5-30 nm) were deposited alternately with Fe and Pt layers on amorphous SiO₂ substrate without any underlayer and then were postannealed at 700°C for 30 min. The dependences of microstructures, degree of ordering, and magnetic properties on FePt film thickness were investigated. The fct-FePt (001) texture films could be obtained by dc magnetron sputtering of (Fe/Pt)_n multilayer on amorphous SiO₂ substrate after annealing at 700°C for 30 min. The increasing degree of L1₀ ordering was probably due to the thicker films providing more L1₀-ordering nucleation sites. The island-like FePt grains formed on the SiO₂ substrates as the film was thinner than 7.5 nm. Both the values of out-of-plane squareness (S_⊥) and coercivity (Hc_⊥) were higher than those of in-plane ones for all film thicknesses. The values of S_⊥ are close to 1 and Hc_⊥ are in the range of 9.0-15 kOe for FePt thin films with a thickness of 5-15 nm after annealing at 700°C for 30 min.