Enhanced structural and magnetic ordering of FePt/Mn-oxide bilayers by ion-beam bombardment and annealing

Abstract

Structural and magnetic properties of FePt thin films were affected strongly by capped MnO x layers prepared by ion-beam bombardment and post-annealing. As-deposited FePt/MnO x bilayer exhibited a magnetically soft fcc phase, and it turned to an ordered fct FePt phase with large coercivity (∼8 kOe) after annealing at 550°C. Increasing the %O 2/Ar in capped MnO x layer during deposition resulted in smaller ordered FePt grains separated by grain boundaries of MnO x. We found that the superlattice (001) peak is broadened considerably with larger amount of MnO x incorporated into FePt, likely due to the hindered formation of hard phase. Our results indicate that FePt/MnO x films deposited with lower %O 2/Ar, the oxygen atoms may occupy the interstitial positions in the FePt lattice to induce a local strain thus enhancing the FePt ordering. Further increased %O 2/Ar in capped MnO x layer, the excess oxygen atoms act a diffusion barrier effectively to inhibit the FePt grain growth and ordering. © 2011 IEEE.