Use of Cernox thermometers in AC specific heat measurements under pressure

Abstract

We report on the resistance behavior of bare-chip Cernox thermometers under pressures up to 2 GPa, generated in a piston-cylinder pressure cell. Our results clearly show that Cernox thermometers, frequently used in low-temperature experiments due to their high sensitivity, remain highly sensitive even under applied pressure. We show that these thermometers are therefore ideally suited for measurements of heat capacity under pressure utilizing an ac oscillation technique up to at least 150 K. Our Cernox-based system is very accurate in determining changes of the specific heat as a function of pressure as demonstrated by measurements of the heat capacity on three different test cases: (i) the superconducting transition in elemental Pb (T c = 7.2 K), (ii) the antiferromagnetic transition in the rare-earth compound GdNiGe 3 (T N = 26 K) and (iii) the structural/magnetic transition in the ironpnictide BaFe 2 As 2 (T s,N = 130 K). The chosen examples demonstrate the versatility of our technique for measuring the specific heat under pressure of various condensedmatter systems with very different transition temperatures as well as amounts of removed entropy. 1 arXiv:1901.05089v2 [cond-mat.mtrl-sci]

Multiple ferromagnetic transitions and structural distortion in the van der Waals ferromagnetVI3at ambient and finite pressures

“…Details of the setup and the measurement protocol are described in Ref. 25. A hybrid piston-pressure cell, made out of Grade 5 titanium alloy (Ti 6Al-4V; outer cell body) and Ni-Cr-Al alloy (inner cell body) 26 , was used to apply pressure up to 2.08 GPa.…”

Hydrostatic and Uniaxial Pressure Tuning of Iron‐Based Superconductors: Insights into Superconductivity, Magnetism, Nematicity, and Collapsed Tetragonal Transitions

“…In our efforts to determine the phase diagram of iron-based superconductors under hydrostatic pressure, which typically undergo a cascade of phase transitions over wide temperature ranges, we recently reported on an optimization of the thermometry of such an ac calorimetry setup to measure specific heat over wide temperature ranges in conventional piston-pressure cells up to 2.5 GPa ( Figure 2). [103] By utilizing commercially available Cernox thermometers to pick up the temperature oscillations of the sample, we demonstrated that we can measure the specific heat of a sample of interest over a temperature range as wide as up to 150 K (and likely even larger). In Sections 3 and 4, we will show how our combined efforts of transport and thermodynamic investigations under hydrostatic pressure (in particular those of the specific heat, using the aforementioned optimized ac calorimetric technique) have advanced the understanding of the phase diagrams of several iron-based superconductors.…”

“…Uniaxial pressure is distinct from hydrostatic pressure, as the applied force, which acts on the crystal, is highly directional. [103] Copyright 2019, AIP Publishing.…”

“…Motivated by the search for bulk superconductivity, we performed a thermodynamic investigation of the temperaturepressure phase diagram up to a pressure of p ≈ 2.36 GPa by utilizing measurements of the specific heat, C. [160] These data were obtained by the technique of ac calorimetry, which was introduced in Section 2. The optimized thermometry of our setup [103] was highly beneficial for this study, since it allows the study of the specific heat of one single sample under pressure from low T, below the superconducting T c , to temperatures as high as at least 100 K, that is, much higher than T s at ambient pressure, as can be seen in example data sets of C∕T versus T in Figure 3b. This therefore allows the identification of all the salient phase transitions which are associated with the temperature-pressure phase diagram of FeSe.…”

Physical properties of RBi2 (R=La,Ce) under pressure

“…Specific heat measurements under pressure were performed using an ac calorimetry technique on a third sample (sample S3) in a cryogen-free cryostat from ICEOxford (Lemon-Dry) with base temperature of 1.4 K. Details of the setup used and the measurement protocol are described in Ref. 23.…”