Heavy-fermion behavior of itinerant frustrated systems: (beta)-Mn, Y(Sc)Mn2, and LiV2O4

These three metallic systems do not exhibit any magnetic ordering despite experiments showing the existence of localized moments with large anti-ferromagnetic exchange: we propose that this is a direct consequence of the strong geometric frustration since Y(Sc)Mn2 and LiV2O4 have the pyrochlore structure, while (beta)-Mn has a more complicated frustrated structure. Another similarity between these compounds is their very large specific-heat coefficient (gamma)=C/T (420 mJ mol–1 K–2 for LiV2O4). Several explanations have been proposed for this "3d heavy-fermion behavior", including a 3d-Kondo effect. However, the similarities between the three compounds indicate that frustration plays a big role. We describe a new model in which we take into account the existence of two types of 3d-electrons (localized and itinerant) and a frustrated anti-ferromagnetic exchange between the localized 3d electrons.