Low temperature calorimetric and magnetic properties of Al-Mn and Al-Mn-Si quasi-crystals

We report on the low temperature specific heat C_p and magnetic measurements for the following Al-Mn alloys: solid solution Al-3at.%Mn, Al₈₆Mn₁₄ and Al₇₅Mn₂₀Si₅ in quasi-crystalline phases. From the amplitude of the electronic specific heat determined below 0.3 K, we propose, in agreement with the electrical resistivity values, that the large density of states in the quasi-crystalline phases are due to virtual bound states related to a regime of isolated manganese “impurities”. Both C_p and magnetic measurements indicate a rapid evolution of the magnetic interactions from Al₈₆Mn₁₄ to Al₇₅Mn₂₀Si₅. In the latter, the _ξac data together with the nuclear magnetic hyperfine specific heat confirm a spin glass state similar to that of canonical spin glasses such as Cu-Mn and Au-Mn. We emphasize that a small fraction of Mn s atoms are magnetic sites (probably less than 10%) in both quasi-crystalline phases.