Thermal contact between cerium magnesium nitrate and liquid3He at very low temperatures

Abstract

A new experimental arrangement has been used to measure the times for equilibrium between cerium magnesium nitrate (CMN) and liquid3He. Measurements have been made on a single crystal of CMN from temperatures of 5.5–15 mK and on a powdered specimen from temperatures of 2.5–35 mK. The thermal resistance deduced from the single-crystal data is proportional toT −2. The thermal resistance obtained from the powder data may be separated into three contributions: a resistance which is proportional toT −2in series with a parallel combination of a phonon resistance (with resistivity ρ P =3×10 −4 T −3sec·cm2·K 4 ·erg −1 ) and a magnetic resistance (with resistivity ρ M =9×10 2 T sec·cm 2 ·erg −1 in zero applied magnetic field). A reduction in the magnetic resistance was observed when the powdered CMN was placed in a magnetic field, the magnitude of this reduction being comparable to that expected from a Redfield-like theory. TheT −2resistance is discussed in terms of two-dimensional energy transport within the CMN. The 17-Hz susceptibility of the powdered CMN was measured in magnetic fields of 0, 18.9, 30.2, and 37.8 G. The magnetic temperatureT* (H=37.8 G) was found to differ by +0.5 mK from the magnetic temperature in zero field whenT* (H=0)=3 mK.