Magnetic field dependence of the thermal conductivity in EuxSr1-xS

The thermal conductivity κ of two Eu_xSr_1-x single crystals (x = 0.25 and 0.54) was measured between 1.5 and 25 K. In magnetic fields of ≈ 7 T κ is enhanced for temperatures up to 20 K with respect to κ(B = 0). At 1.5 K, where the relative increase κ(B)/κ(0) is largest, this ratio is 1.5 for x = 0.54 and ≈ 4 for x = 0.25. Two possible mechanisms for this effect, i.e. freezing of phonon scattering by magnetic excitations in a magnetic field, and heat transport by field-induced magnons, are discussed.