We report on the experimental realization of tetragonal Fe-Co alloys as a constituent of ${\mathrm{Fe}}_{0.36}{\mathrm{Co}}_{0.64}/\mathrm{Pt}$ superlattices with huge perpendicular magnetocrystalline anisotropy energy, reaching $210\mu \mathrm{eV}/\mathrm{\text{atom}}$, and a saturation magnetization of $2.5{\mu }_{\mathrm{B}}/\mathrm{\text{atom}}$ at 40 K, in qualitative agreement with theoretical predictions. At room temperature the corresponding values $150\mu \mathrm{eV}/\mathrm{\text{atom}}$ and $2.2{\mu }_{\mathrm{B}}/\mathrm{\text{atom}}$ are achieved. This suggests that Fe-Co alloys with carefully chosen combinations of composition and distortion are good candidates for high-density perpendicular storage materials.

• Received 7 September 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.037205