Development of a relaxation calorimeter for temperatures between 0.05 and 4 K

Abstract

A detailed description of an isoperibol calorimeter for temperatures between 0.05 and 4 K is presented. The proposed setup can provide absolute values of the heat capacity C of small samples (typically 1 mg). The extremely simple design of the sample platform, based on a sapphire substrate, and the experimental setup, which makes use only of a lock-in amplifier and a temperature controller, make the construction of such a calorimeter easy and inexpensive. The thermal-relaxation method is employed, which utilizes a permanent thermal link k between the sample platform and the low-temperature bath. The temperature dependence of k(T) is shown for several platforms throughout the entire temperature range: k(T)/T is nearly constant down to 1 K, where it starts to decrease smoothly. The observed behavior is thoroughly explained by considering the thermal resistances of the platform constituents. A comparison between the values of k(T)/T for platforms based on sapphire and on silver is presented where no significant difference has been observed. Each platform can be assembled to have a particular value of k/T at 1 K. Since the sample relaxation time tau approximately C/k, k(T) can be adjusted to C(T) to give a reasonably fast measuring time. Here, it is demonstrated how this calorimeter can be used in so-called single-shot refrigerators ((3)He or demagnetization cryostats), where the time for a single measurement is limited. In addition, it can be used in moderate magnetic fields B<or=10 T, because the platform constituents are weakly field dependent.

Specific Heat Determination of Metallic Thin Films at Room Conditions

“…A similar tendency was observed by Lai et al [32] by using a differential scanning calorimeter for Sn samples with thickness from 0.1 to 2 nm, and by Yu et al [17] for Cu films with thickness from 20 to 320 nm and a microcalorimeter at vacuum conditions. The reported values were estimated from the mean heating profiles of three pulses of different times (20,40, and 100 ls). From Fig.…”

“…Thus, several calorimeters for specific heat determination have been reported for different temperature conditions and film thickness values [19][20][21][22]. Normally, specific heat of thin films is usually measured under low vacuum conditions and controllable atmosphere.…”