Complex Magnetic Behavior of the Ce sawtooth chains in CeRhSn${}_2$

Abstract

Conflicting reports exist on the ground state of the intermetallic compound CeRhSn${}_2$. This can be rooted in the sawtooth-like arrangement of two inequivalent Ce sites in the unit cell, which suggests potential geometric magnetic frustration. To resolve, we conducted a comprehensive study on high-quality single crystals of CeRhSn${}_2$ by means of magnetization ($M$), specific heat ($C_p/T$), and resistivity ($\ddot{I}$). The system exhibits strong magnetic anisotropy, confirming the $b$-axis as the easy magnetic axis. We establish three successive transitions, an AFM order at $T_N=3.65$K, a first-order FM order at $T_C=1.7$K and final transition, at $T=1.5$K. The transition temperatures are highly field-directional dependent: in a magnetic field, the lowest transition is immediately suppressed while $\mathbf{H}\parallel b$ rapidly merges $T_C$ and $T_N$ into a single second-order transition. Conversely, $\mathbf{H}\parallel c$ suppresses the FM order and reduces $T_N$. Additional ab initio calculations affirm the FM ground state of CeRhSn${}_2$. The observation of an enhancement of the Sommerfeld coefficient (${\hat{I}}^3=76.5$mJ/mol$\cdot$K${}^2$) may arise from geometric frustration, but it is most consistently attributed to weak Kondo hybridization as frustration cannot be conclusively established through our data.

10 pages, 8 figures, accepted for publication in Phys. Rev. B