Anomalies in the thermal resistivity of praseodymium ethylsulphate below 4 K.

The magnetic field dependence of the thermal conductivity of praseodymium ethylsulphate has been measured between 0.4 and 4 K. Results below 1K can be explained in terms of phonon scattering between magnetic levels. Above 1K anomalies occur for which a satisfactory explanation is not yet available, although they seem to have some connection with extra lines observed in the optical spectru