The thermal conductivity of double nitrate crystals below 1 K

The thermal conductivity was measured in Lanthanum Magnesium Nitrate (LMN) and Cerium Magnesium Nitrate (CMN) in zero external magnetic field and was found to be independent of the particular rare-earth ion which occupied the La site, the concentration of that ion, the thickness of the sample and the condition of its surfaces. The thermal conductivity, measured both in the direction perpendicular to that axis, was observed to vary according to a power of the temperature which lay between 2.8 and 3.0'. It is suggested therefore that the thermal conductivity in the double nitrate crystals is determined by an internal scattering mechanism which is approximately independent of frequency. The phonon mean free paths, calculated in the usual way from the thermal conductivities of the individual samples, were appreciably greater than the smallest dimensions of the respective samples. A depression observed in the thermal conductivity of samples doped with the non-Kramers rare-earth ions Pr+3 and Ho+3 was determined to be caused by the resonant scattering of phonons by these ions due to electronic transitions between the magnetic hyperfine levels. The splitting, in zero external magnetic field, between the hyperfine levels in the Pr+3 ion inCMN is 0.048 K. This splitting in the Ho+3 ion inLMN is estimated to be on the order of or less than 0.03 K.U of I OnlyThesi