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.