We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of $26\mathrm{\text{Tera}}/{\mathrm{in}}^2$ ($1\mathrm{Tera}={10}^{12}$), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. $\mathrm{Co}/\mathrm{Au}(788)$ thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.

• Received 3 March 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.157204