The magnetic anisotropy energy is among the most important functional properties of magnetic elements. It determines the orientation and stability of the magnetization as well as the mechanisms and the dynamics of the magnetization reversal. New materials with extremely large anisotropy values are currently sought for the development of ultrahigh density magnetic recording media. As one example, FePt or CoPt alloys exhibiting L10 structure are currently in the focus of intensive research, as they were found to exhibit unprecedented anisotropy values. Recently Nebraska MRSEC researchers in collaboration with their international partners at Stuttgart, Vienna and München have discovered that atomically small nanostructures of Fe and Pt can also, under certain conditions, exhibit magnetic anisotropy values similar to those of their L10 bulk counterparts (Phys. Rev. Lett. 102, 067201, (2007)). This discovery was possible after advances in nanostructure synthesis have been made to embed Fe atoms as monatomic Fe stripes or in other configurations into the surface of Pt single crystals. It was found that the Pt plays a critical role in the magnetism of these structures, as it dictates the structure's magnetic anisotropy and thus helps the Fe to stay magnetized. Intriguingly, in the system studied, there is an interesting interplay between ordinary magnetization states and non-collinear spin structures at the nanoscale, leading to rather complex magnetic properties of the FePt nanostructures.
This research is supported by the National Science Foundation, Division of Materials Research, Materials Research Sciences and Engineering Program, Grant 0820521.
STM image of FePt surface alloy with atomic chemical contrast. The Fe atoms (yellow) are embedded in the Pt surface (bluish, not resolved). Fe chains separated by Pt is the key to large magnetic anisotropy.