Complex magnetic phase diagram in Ce 3 Pd 6 Sb 5 with a well-ordered superstructure

We report multiple magnetic phase transitions in single-crystalline ${\mathrm{Ce}}₃{\mathrm{Pd}}₆{\mathrm{Sb}}₅$ using magnetic, transport, and thermodynamic measurements. ${\mathrm{Ce}}₃{\mathrm{Pd}}₆{\mathrm{Sb}}₅$ crystallizes in an orthorhombic structure (space group Pmmn), as a defect-induced variant of the well-known tetragonal ${\mathrm{CaBe}}₂{\mathrm{Ge}}₂$ structure. It undergoes two magnetic transitions: a second-order antiferromagnetic transition at ${T}_{\mathrm{N}1}$ = 6.6 K and a first-order one at ${T}_{\mathrm{N}2}=5.8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The hybridization between $4f$ electrons and conduction electrons is relatively weak in ${\mathrm{Ce}}₃{\mathrm{Pd}}₆{\mathrm{Sb}}₅$, as revealed from the nearly full recovery of magnetic entropy $R\mathrm{ln}2$ at ${T}_{\mathrm{N}1}$ and the low value of the electronic specific-heat coefficient of 30 mJ/(Ce-mol ${\mathrm{K}}²$). We construct two field-temperature phase diagrams for magnetic fields applied parallel and perpendicular to the $c$ axis, which, for $H\ensuremath{\parallel}c$, shows multiple field-induced phases between ${T}_{\mathrm{N}1}(H)$ and ${T}_{\mathrm{N}2}(H)$, while Hall resistivity measurements point to the absence of a topological Hall effect. The crystalline electric field effect and modulated crystalline structure with two Ce sites are considered as the primary factors for the complex magnetic properties of ${\mathrm{Ce}}₃{\mathrm{Pd}}₆{\mathrm{Sb}}₅$.