Induced-moment systems: paramagnetic region of La3Tl--Pr3Tl

Superconducting and magnetic properties in the La₃Tl-Pr₃Tl system are discussed. Superconductivity persists up to very high Pr concentrations, Pr³⁺ being in a crystal-field-singlet ground state. The Van Vleck susceptibility per Pr³⁺ ion at T=0 increases with increasing Pr concentration, indicating ferromagnetic exchange coupling between the Pr ions. At concentrations higher than 93-at.% Pr the system becomes ferromagnetic. No current theoretical model accounts for the observed magnetic behavior.