Frustrated Antiferromagnetism and Heavy-Fermion-like Behavior in PrPdAl

We report on the long-range antiferromagnetic ordering with two successive phase transitions at T-N1 = 4.0 K, T-N2 approximate to 1.3 K and the heavy-fermion-like behaviors in PrPdAl, a Kondo lattice with kagome-like structure of non-Kramers Pr ions in the hexagonal basal plane. The ground-state antiferromagnetism forms by two-thirds Pr ions with nearly full magnetic moment and one-third with strongly frustrated and reduced moment. The easy magnetization axis points along c whereas the ordered Pr 4f moments reside in the basal plane, mirroring the important effect of spin frustrations. The electronic specific-heat coefficient is strongly enhanced to similar to 940 mJ/mol K-2, and the Kadowaki-Woods ratio is factor-of-25 smaller than that of conventional heavy-fermion compounds with Kramers doublet ground state. The effective Grfineisen ratio estimated from thermal expansion reveals large values in the vicinity of the broadened phase transition at T-N2, manifesting its instability against pressure. Accordingly, PrNiAl, a chemically pressurized analog of the titled compound, was found to reveal only one antiferromagnetic transition at a considerably higher temperature of 6.9 K. These results demonstrate that PrPdAl and related homologues can offer excellent cases for investigating competing ground states in frustrated Kondo lattices formed by non-Kramers magnetic ions.