Cascade of Magnetic Transitions in the Frustrated Antiferromagnetic CePtPb

Synopsis

CePtPb is an antiferromagnetic, heavy-fermion, metallic compound that crystallizes in the ZrNiAl-type structure with space group P-62m, where the Ce-ions form a quasi-Kagome lattice in the ab-plane. Other compounds in this family with a quasi-Kagome magnetic lattice such as CePdAl and YbAgGe have shown a complex temperature-versus-magnetic field (T-H) phase diagram with multiple magnetically-ordered phases. In this thesis, a T-H phase diagram for single crystal CePtPb is constructed from electric resistivity and specific heat measurements. The constructed phase diagram also shows multiple magnetically-ordered phases as the Neel temperature TN = 0.9 K is suppressed continuously to T = 0.4 K by applied field with an extrapolated zero-temperature critical field H_c = 7 kOe. In zero-field, muon spin relaxation measurements show residual spin dynamics at 25 mK, consistent with the magnetic structure proposed for CePdAl, where 2/3 of the Ce-4f spins order antiferromagnetically and the other 1/3 of the Ce-4f spins remain fluctuating. From a power-law analysis of the electrical resistivity (p=p_0+AT^n), neither Fermi-liquid (n = 2) nor non-Fermi-liquid (n < 2) behaviour have been observed down to T = 0.4 K for H >= H_c. Instead, there is an anomalous evolution of n that increases from n = 2.5 at H = H_c to n = 4.1 at H = 90 kOe, with a tendency towards saturation near the value n = 4 for H > 30 kOe. The phase diagram and the measurements are compared to CePdAl and YbAgGe.