Hard ferromagnetism in two-dimensional FePt surface alloys

The rapidly increasing information density in magnetic storage media during the last decades is an achievement of the successful down-scaling of bit structures into the submicrometer regime. However, limits are set to further miniaturization by thermal excitation of the spins, decreasing the stability of the magnetically stored information. The challenge for scientists is in achieving stable magnetization in nanostructures with respect to temperature and other external factors that may lead to erasure of magnetically stored information. In this respect, FePt alloys are extensively studied by industry and applied physics research groups due to their large magnetocrystalline anisotropy. In our experiments we concentrated on two-dimensional surface-supported alloy layers and found that these films achieve anisotropy energy values comparable to those of bulk L10 structures. We will show that the detailed analysis of the properties of alloy nanostructures can help to identify principles to design high-anisotropy materials.