Electronic excitations at the threefold-symmetric surface of the quasicrystal Al–Pd–Mn

In the search for the electronic origin of the peculiar magnetic behavior of the Al70Pd20Mn10 quasicrystal, we have performed electron energy-loss spectroscopy measurements on a surface, oriented perpendicular to one of the threefold-symmetry directions of this icosahedral alloy. Two different surface structures, a cubic and a quasicrystalline surface phase, are induced by Ar+ ion bombardment and annealing on the same bulk quasicrystal. Comparative measurements on these surfaces indicate that the 3p–3d transition in the quasicrystal is so weak that it is effectively masked by plasmon excitations. This transition would disappear for a fully occupied 3d band and, for this case, local magnetic moments at the Mn site would be quenched.