Suppresssion of thermal conductivity by magnetic singlets in TmFeO₃ and implications for quantum magnetism

We report the thermal conductivity (κ) of the rare-earth orthoferrites, RFeO₃, where R = Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb from 3 K to 300 K, An anomalous strong suppression of κ for TmFeO₃ over most of the temperature range is observed. Using a Debye thermal transport model, we demonstrate that this suppression is due to resonant scattering between phonons and the Tm³⁺ 4f singlet crystal field levels. The implications of these results for thermal conductivity studies in quantum magnets where interatomic singlets likely form the basis for collective beahvior is disucessed.