EFFECT OF ICOSAHEDRAL AND CUBOCTAHEDRAL SYMMETRIES ON THE ELECTRONIC AND MAGNETIC-STRUCTURE OF MNAL(N)

The effect of local symmetry on the magnetic moment at the Mn sites in MnxAl1-x quasicrystals has been investigated by modeling the quasicrystals by clusters. Our studies based on the self-consistent density-functional calculations on clusters having a central Mn surrounded by Al(n) (n less-than-or-equal-to 54) atoms in cuboetahedral and icosahedral arrangement show that the Mn sites do carry a moment at small cluster sizes. The moment is, however, quenched as the cluster size is increased irrespective of the geometry. This quenching is shown to be a direct consequence of the mixing between the Mn d states and the Al p states in these geometries. The existing theoretical picture, which is based on calculations on smaller clusters and predicts that the magnetic Mn sites in MnAl quasicrystals are a result of icosahedral symmetry, is shown to be incorrect.