Magnetic thermometry to below one millikelvin with lanthanum-diluted cerium magnesium nitrate

Abstract

Measurements are presented of the pressure and magnetic temperature coordinates of the phase diagram of liquid 3He using a powdered CeoosLao.9s magnesium nitrate thermometer in the shape of a right circular cylinder with diameter equal to height. The lowest magnetic temperature observed with the thermometer is 0.41 inK. The magnetic temperature of the intersection of the second-order line with the melting curve is 2.625mK, and the critical temperature at zero pressure is 1.055mK. The difference between To* and TaB* extrapolated to melting pressure is 0.57 mK, in excellent agreement with the difference TA --T~ found from measurements along the melting curve. The present data are compared with the La Jolla provisional absolute scale based on noise thermometry and zero sound. We make the assumption that the absolute temperature T and the present magnetic temperature T* are related by T = T* + A and use the resultant scale to reanalyze a variety of experimental results that had been given in terms of the La Jolla provisional scale.

A microkelvin cryogen-free experimental platform with integrated noise thermometry

“…Other convenient methods of temperature measurement, such as carbon resistance sensors [24], shot noise in tunnel junctions [25] or Coulomb blockade [26] also prove difficult to implement below a few mK. The most common approach is to rely on the Curie-law paramagnetism of nuclear spins [27] or the magnetism of dilute electronic paramagnets [28] calibrated with a fixed point device. Other methods are possible if a sample of superfluid 3 He is part of the set-up [29].…”

On the use of CMN thermometry in specific heat measurements below 10 mK

“…It has been shown [7] that this P-T relation can be established through application of the second law of thermodynamics and measurements of the latent heat of solidification of 3He. Two more recent thermometry techniques based on 195pt nuclear magnetic resonance [8] and the susceptibility of La diluted CMN [9] appear to give results consistent with the melting curve scale. At the time that the melting curve work was done an attempt was made [7] to relate this new temperature scale to that of CMN, which was then the prevalent thermometric technique.…”

A magnetically diluted CMN thermometer

“…A negative value of d would affect the proposed phase diagram of Paulson et al [4], who used a similar thermometer and assumed d = + 0.10 mK, and might even remove the discrepancy between their temperatures and the Helsinki scale [5]. However, there is no reason why L1 should be the same for different samples and in our case at least trapped flux may be causing the salt to behave anomalously.…”