Gambardella, P.Rusponi, S.Veronese, M.Dhesi, S. S.Grazioli, C.Dallmeyer, A.Cabria, I.Zeller, R.Dederichs, P. H.Kern, K.Carbone, C.Brune, H.2009-04-142009-04-142009-04-14200310.1126/science.1082857https://infoscience.epfl.ch/handle/20.500.14299/37177WOS:0001828865000403689The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum ( 111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops infinite-sized magnetic particles.Magnetism at the Atomic Leveltext::journal::journal article::research article