Low-temperature antiferromagnetic order in orthorhombic CePdAl${}_3$

Abstract

We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of CePdAl${}_3$. In comparison to the properties of polycrystalline 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 order antiferromagnetically below a Néel temperature $T_{\mathrm{N}}$ = 5.6 K. The specific heat at zero-field shows a clear $\hat{I}»$-type anomaly with a broad shoulder at $T_{\mathrm{N}}$. A conservative estimate of the Sommerfeld coefficient of the electronic specific heat, ${\hat{I}}^3=121\mathrm{mJ}{\mathrm{K}}^{-2}\mathrm{mo}{\mathrm{l}}^{-1}$, indicates a moderately enhanced heavy-fermion ground state. A twin microstructure evolves in the family of planes spanned by the basal plane lattice vectors $a_{\mathrm{o}}$ and $c_{\mathrm{o}}$, with the magnetic hard axis $b_{\mathrm{o}}$ common to all twins. The antiferromagnetic state is characterized by a strong magnetic anisotropy and a spin-flop transition induced under magnetic field along the easy direction, resulting in a complex magnetic phase diagram. Taken together our results reveal a high sensitivity of the magnetic and electronic properties of CePdAl${}_3$ to its structural modifications.