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

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FePt thin films with different thicknesses (2.5-30 nm) were deposited alternately with Fe and Pt layers on amorphous SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> multilayer on amorphous SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrate after annealing at 700°C for 30 min. The increasing degree of L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ordering was probably due to the thicker films providing more L1 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> -ordering nucleation sites. The island-like FePt grains formed on the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrates as the film was thinner than 7.5 nm. Both the values of out-of-plane squareness (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> ) and coercivity (Hc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> ) were higher than those of in-plane ones for all film thicknesses. The values of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> are close to 1 and Hc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> 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.