Unexpected heavy-electron behavior at low temperatures in PrInAg 2

Abstract

Specific heat, magnetic susceptibility, and electrical resistivity were measured as a function of temperature in polycrystalline PrInAg 2. A broad peak, similar to a conventional Kondo anomaly, occurs in the specific heat at 400 mK. Below the peak, an enhanced linear contribution is observed with a Sommerfeld coefficient of ∼ 6.5 J/mol K 2. This is the first Pr-based compound to display heavy-fermion behavior, and it has a Kondo temperature of ∼ 1 K. Inelastic -neutron-scattering experiments by Galera et al. found that the non-Kramers doublet ( Γ 3) in PrInAg 2 is the ground state with a first excited level at 5.9 meV. Since the ground state does not have a magnetic moment, our results point to the possibility of a new type of interaction between the conduction electrons and the quadrupolar moments of the localized 4f electrons. The magnetic susceptibility follows a Curie-Weiss law above ∼ 50 K with an effective moment of 3.67 μ B. At low temperatures, the susceptibility falls below simple Curie-Weiss behavior, and it has a value close to that estimated for a Van Vleck contribution with the crystal electric field levels observed in neutron scattering. The electrical resistivity monotonically decreases with temperature and then saturates below ∼ 10 K. A weak decrease is observed in the resistivity around 1 K which is consistent with the small Kondo temperature.