Conditions on the Occurrence of Magnetic Moments in Quasicrystals and Related Phases

We analyze the criterion for the appearance of magnetic moments in quasicrystals approximants and liquids Al-Mn. In a Hartree-Fock scheme, it is shown that the Stoner criterion (Un_d(E_F) > 1) does not apply to these systems due to the presence of the pseudogap in the density of states. We give an generalized criterion that can take into account the particular density of state. The main result is that the appearance of a magnetic moment on a Mn atom depends strongly on its position in the crystalline structure. Indeed some particular positions of the Mn atoms lead to magnetic moments whereas other positions are more stable when the Mn is non-magnetic. This criterion is used to analyzed the electronic structure of two approximants (1/1-Al-Pd-Mn-Si and T-Al-Pd-Mn) calculated by the self-consistent LMTO-ASA method.