Stoichiometry–anisotropy connections in epitaxial L10 FePt(001) films.

The order parameters and anisotropy constants of a series of epitaxial L10 FePt films with compositions in the range of 45–55 at. % Fe and nominal thicknesses of 50 nm have been characterized. The films were made by cosputtering the elements onto single crystal MgO(001) substrates. The substrates were coated with 1 nm Pt/1 nm Fe bilayer seeds prior to alloy deposition. Both the bilayer seed and the alloy film were deposited at 620 °C. Lattice and order parameters were obtained by x-ray diffraction. Film compositions and thicknesses were determined by Rutherford backscattering spectrometry, and room-temperature magnetocrystalline anisotropies were determined with a torque magnetometer. It was found that the order parameter had a maximum for the film composition closest to the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the Fe content increased from below to slightly above the equiatomic composition. These results imply that nonstoichiometric FePt compositions, with a slight excess of Fe, may in fact be preferred for applications that require high anisotropy. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]