Transport Thermal Properties of LiTaO3 Pyroelectric Sensor from 15 K to 400 K and Its Application to the Study of Critical Behavior in EuCo2As2

摘要

ac photopyroelectric calorimeters in the standard back configuration, where LiTaO3 is one of the most popular materials to be used as a detector, are commonly used to study phase transitions in solids and liquids. In order to extract the specific heat of a studied sample, a good knowledge of the thermal effusivity of the sensor as a function of temperature is needed. This function has been obtained for the first time in the range 15 K to 400 K by independently measuring LiTaO3 thermal diffusivity and specific heat and combining both of them to give thermal effusivity. Using this photopyroelectric setup and LiTaO3 as sensor, we have carried out the study of the critical behavior of the antiferromagnetic ordering of the Eu2+ spins in EuCo2As2 (a compound with similar structure as EuFe2As2, from which superconductors have been developed) at low temperature by measuring its specific heat. The critical parameters found for EuCo2As2 (alpha = -0.017, A(+)/A(-) = 1.06) agree with the 3D-XY universality class, indicating that the spins present an in-plane arrangement for Eu2+, in agreement with magnetic measurements in the literature.