Structural modification and metamagnetic anomaly in the ordered state ofCeOs2Al10

Abstract

A caged compound ${\text{CeOs}}_{2}{\text{Al}}_{10}$, crystallizing in the orthorhombic ${\text{YbFe}}_{2}{\text{Al}}_{10}$-type structure, undergoes a mysterious phase transition at ${T}_{0}=29\text{ }\text{K}$. We report the results of electron diffraction, magnetization, and magnetoresistance for single crystals. Superlattice reflections characterized by a wave vector $\mathbit{q}=(0,\ensuremath{-}2/3,2/3)$ observed at 15 K indicate a structural modification in the ordered state. Activation-type behavior of the electrical resistivity along the three principal axes below 50 K suggests gap opening in the conduction band. The magnetic susceptibility $\ensuremath{\chi}=M/B$ is highly anisotropic, ${\ensuremath{\chi}}_{a}>{\ensuremath{\chi}}_{c}>{\ensuremath{\chi}}_{b}$, all of which sharply decrease on cooling below ${T}_{0}$. Furthermore, a metamagnetic anomaly in the magnetization and a step in the magnetoresistance occur at $B=6--8\text{ }\text{T}$ only when the magnetic field is applied parallel to the orthorhombic $c$ axis. However, ${T}_{0}$ hardly changes under magnetic fields up to 14 T, irrespective of the field direction. By using these data, we present a $B\text{\ensuremath{-}}T$ phase diagram and discuss several scenarios for the mysterious transition.