Low-temperature antiferromagnetic order in orthorhombic CePdAl3

We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of CePdAl3. In comparison to the properties of polycrystalline CePdAl3 reported in the literature, which displays a tetragonal crystal structure and no long-range magnetic order, our single crystals exhibit an orthorhombic structure (Cmcm) and antiferromagnetic order below a Néel temperature T1=5.6 K. The specific heat at zero field shows two anomalies, namely, a broad transition at T1=5.6 K followed by a λ-anomaly at T2=5.4 K. A conservative estimate of the Sommerfeld coefficient of the electronic specific heat, γ=121mJK-2mol-1, indicates a moderately enhanced heavy-fermion ground state. A twin microstructure evolves in the family of planes spanned by the basal plane lattice vectors ao and co, with the magnetic hard axis bo common to all twins. The antiferromagnetic state is characterized by a strong ao, co easy-plane magnetic anisotropy where the ao direction is the easy axis in the easy plane. A spin-flop transition induced under magnetic field along the easy directions, results in complex magnetic phase diagrams. Taken together, our results reveal a high sensitivity of the magnetic and electronic properties of CePdAl3 to its structural modifications.