Low-temperature antiferromagnetic order in orthorhombic CePdAl3

We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of ${\mathrm{CePdAl}}_{3}$. In comparison to the properties of polycrystalline ${\mathrm{CePdAl}}_{3}$ 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 N\'eel temperature ${T}_{1}=5.6$ K. The specific heat at zero field shows two anomalies, namely, a broad transition at ${T}_{1}=5.6$ K followed by a $\ensuremath{\lambda}$-anomaly at ${T}_{2}=5.4$ K. A conservative estimate of the Sommerfeld coefficient of the electronic specific heat, $\ensuremath{\gamma}=121\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}$, indicates a moderately enhanced heavy-fermion ground state. A twin microstructure evolves in the family of planes spanned by the basal plane lattice vectors ${\mathbf{a}}_{\mathrm{o}}$ and ${\mathbf{c}}_{\mathrm{o}}$ , with the magnetic hard axis ${\mathbf{b}}_{\mathrm{o}}$ common to all twins. The antiferromagnetic state is characterized by a strong a${}_{\mathrm{o}}$, c${}_{\mathrm{o}}$ easy-plane magnetic anisotropy where the a${}_{\mathrm{o}}$ 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 ${\mathrm{CePdAl}}_{3}$ to its structural modifications.