Magnetic Properties of Ultra-Thin FePt Films Grown on Oxidized Si Substrates

Abstract

We report the effects of thickness and post annealing temperature on the structural and temperature dependent magnetic properties of FePt (x = 5–50 nm) thin films deposited at ambient temperature on the oxidized Si substrate with an MgO (y = 5, 10 nm) underlayer. All the as-deposited samples show face centered cubic structure, but transformed into L1₀ ordered structure upon annealing. The formation of L1₀ ordered structure depends strongly on the films thickness and annealing temperature. The coercivity of the FePt films with thickness lower than 20 nm was obtained to be less than 3 kOe, but increases rapidly to above 6 kOe for more thicker films. Room temperature magnetic properties and high temperature magnetic properties of the FePt films were studied by analyzing the magnetization data as a function of temperature to understand the stability of the L1₀ ordered structure. High temperature coercivity variation exhibits a linear variation of coercivity up to 540 K and transforms into soft magnetic phase above 640 K. The obtained results are discussed in correlation with the improvement in the L1₀ ordering with annealing and the reduction in the temperature dependence of magnetocrystalline anisotropy energy.