Thermal Equilibrium Between LiquidHe3and Powdered Cerium Magnesium Nitrate at Very Low Temperatures

Abstract

We have discovered that the thermal relaxation time of a mixture of powdered cerium magnesium nitrate (CMN) and liquid He 3 is anomalously small at very low temperatures. We believe that this effect is important for the future development of experimental physics at low temperatures. It may also be used to explain the heat-capacity results of Peshkov 1 without recourse to the assumption of superfluidity in He 3 . Moreover, a certain interpretation of the experimental results may bear on the temperature dependence of the thermal conductivity of He 3 down to magnetic temperatures of order 2 mdeg K on the temperature scale valid for powdered CMN in the form of a right circular cylinder with diameter equal to height.The observations reported here were obtained from an analysis of the temperature-time curves of the heat-capacity experiment of Abel et al. 2 In this experiment, by a difference method, it was possible to obtain both the heat capacity of the He 3 and of the powdered CMN, the latter being used to cool the He 3 and to measure its temperature. It has long been supposed that the principal thermal resistance between the He 3 and the CMN is the Kapitza thermal boundary resistance, although the latter is very poorly understood from an experimental viewpoint. 3 A bath of He 3 and a bath of CMN would come to thermal equilibrium in a timewhere R is the thermal resistance between the two baths (ocT~3 for a "normal" Kapitza resistance 3 ), C 3 is the heat capacity of He 3 (nearly proportional to T at low T), and C^MN is tne heat capacity of the CMN (nearly proportional to T~2 at high temperatures). Thus if R is the Kapitza resistance, one expects roc T~5 a t high temperatures and r oc T~2 at low temperatures. The experimental results for r are shown in Fig. 1. Neither of the above limits is observed, but rather a maximum in r is found, the actual values of r being remarkably short for the present temperature range and the size and heat capacity of the sample. 273

On the anomalous CMN-He3 3 thermal boundary resistance

“…In 1966, Abel et al 2 discovered that the Kapitza resistance between the dilute magnetic salt cerium magnesium nitrate (CMN) and pure liquid He 3 between 2 and 20 mdeg is not only orders of magnitude smaller than in any other known case at these temperatures, but appears to decrease linearly with T. No similar anomaly was found in experiments 3 on dilute solutions of He 3 in He 4 which went down to 10 mdeg. The measurements of Abel et al 2 were made on samples in which He 3 penetrated into the pores in powdered CMN, and at first there was some suspicion that the true surface area of the pores had been grossly underestimated.…”

“…In 1966, Abel et al 2 discovered that the Kapitza resistance between the dilute magnetic salt cerium magnesium nitrate (CMN) and pure liquid He 3 between 2 and 20 mdeg is not only orders of magnitude smaller than in any other known case at these temperatures, but appears to decrease linearly with T. No similar anomaly was found in experiments 3 on dilute solutions of He 3 in He 4 which went down to 10 mdeg. The measurements of Abel et al 2 were made on samples in which He 3 penetrated into the pores in powdered CMN, and at first there was some suspicion that the true surface area of the pores had been grossly underestimated. If this were so, the CMN-He 3 boundary resistance proper might give a negligible contribution to the observed temperature drop between the bulk liquid and the CMN, which would then be governed mainly by the intrinsic thermal resistivity of the liquid in the pores; since the latter is known to be proportional to T, this would explain the observed anomalous temperature dependence.…”

Review paper: Heat transfer between liquid helium and solids below 100 mK

“…Following the work of Abel et al 110 was well separated from the sample, so that a magnetic field could be applied to the sample without affecting the thermometer.…”

Spin relaxation of 3He to paramagnetic centers in surfaces at very low temperatures

“…The difference in prefactors is probably a consequence of the slightly different effective distances of the closest approach of the 3He spins to the electron spins, which changes the effective dipole-dipole strength. (b) In (39) it was implicitly assumed that toe/kFvv << 1. In (B 16) we have relaxed this assumption.…”

“…In (B 16) we have relaxed this assumption. Consequently, the last term in (39) corresponds to the last several terms of (B16). When we/kFVF<< 1, both expressions for 1/T1 are identical except for the numerical prefactor.…”