Thermodynamic Investigation of Metamagnetic Transitions and Partial Disorder in the Quasi-Kagome Kondo Lattice CePdAl

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Low-temperature (T) thermodynamic properties in magnetic fields (B) of the quasi-Kagome antiferromagnet CePdAl (T N 2.7 K) were studied by means of magnetization and specific-heat C(T,B) measurements. The unusual magnetic phase diagram, including three thermodynamic phases I-III, and crossover anomalies, has been obtained. In low-field phase I, the existence of the partial Kondo screening state on the one-third Ce sites is supported from the thermodynamic point of view: (i) an appearance of the paramagnetic moment with one-third of the full moment around 3 T, and (ii) an occurrence of the entropy release 0.3Rln2 around the observed crossover. On the other hand, a strong enhancement of C/T is found around the point, where T N(B) meets the boundary of phase III, indicating the possible presence of a tri-critical point. Furthermore, it is suggested that the three metamagnetic transitions at B mi (i=1,2,3) come from successive increments of the Ising-type magnetic moment along the c-axis. In high-field state above 20 T, the behavior of f electron can be rather described by the crystal-electric-field model.