Enhanced Structural and Magnetic Ordering of FePt/Mn-Oxide Bilayers by Ion-Beam Bombardment and Annealing

摘要

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