Structural perfection and the electrical and magnetic responses of icosahedral AlPdMn quasicrystals

Abstract

According to reports in the literature, icosahedral i-AlPdMn quasicrystalline samples of a similar composition can exhibit very different magnetic and electrical properties, for example, the spin-glass state, the Kondo compensation of Mn magnetic moments, diamagnetism, and the maximum and minimum in the electrical resistivity. In order to shed light on the origin of these differences, we performed x-ray diffraction (XRD), electrical resistivity, magnetic susceptibility, and nuclear magnetic resonance (NMR) relaxation studies on three i-AlPdMn samples with high structural quasiperiodic order that were grown by two different techniques-the Czochralski and the self-flux. The measured parameters-the resistivity with its negative temperature coefficient, the fraction of magnetic Mn atoms, and the partial s-state electronic density of states (s-DOS)--of the investigated samples were found to be quite different, despite their comparable XRD-determined structural qualities. The Czochralski-grown samples were found to be less magnetic and more resistive than the self-flux-grown sample. The amount of magnetic Mn atoms increases with the increased metallic character of the samples. The NMR-determined s-DOS at the Fermi energy was compared to a theoretical ab initio calculation for an Al 7 1 Pd 2 1 Mn 8 approximant, and good agreement was found. Our results are in qualitative agreement with the previously observed empirical trend that high resistivity is associated with high structural quality of the i-AlPdMn quasicrystals, but the observed small differences in the structural perfection of the investigated samples do not give convincing support to the hypothesis that this could be the main origin of the large differences in the electrical and magnetic response between the samples.