A comparative study of ultra-low-temperature thermal conductivity of multiferroic orthoferrites RFeO3 (R = Gd and Dy)

Ultra-low-temperature thermal conductivity (κ) of GdFeO3 and DyFeO3 single crystals is studied down to several tens of milli-Kelvin. It is found that the κ is purely phononic and has strong magnetic-field dependence, indicating a strong spin-phonon coupling. Moreover, the low-T κ(H) with H∥c show rather different behaviors in these two materials. In particular, the κ of GdFeO3 can be strongly enhanced in several tesla field and becomes weakly field dependent in higher fields up to 14 T; whereas, the κ of DyFeO3 is continuously suppressed with increasing field and does not show any signature of recovery at 14 T. The results can be well understood by the difference in the spin anisotropy of Gd3+ and Dy3+ ions.