A new application of the liquid thermoelectrics: The detection of magnetic phase transitions

During last years, both solid and liquid thermoelectric materials proved to be useful tools for thermal inspection of condensed matter samples. Used in contact techniques, the liquid thermoelectrics are very suitable in investigating the thermal properties of solids, mainly due to the perfect solid sample-liquid sensor thermal contact. The paper proposes a new application of the liquid thermoelectrics (LTE): the detection of phase transitions. In order to prove the suitability of this application, Cr2O3 single crystal was selected as a sample - Cr2O3 is a well-known antiferromagnetic material involved in a phase transition at a Néel temperature around 34 °C. A LTE material (octanol + 10−2 mol/l tetrabutylammonium nitrate (TBAN)) was used as a sensor for the detection of the antiferro-paramagnetic phase transition of Cr2O3. Based on the recently developed theory of the photothermoelectric (PTE) method, the measured amplitude and phase of the complex PTE signal were converted in thermal parameters. As a consequence, the behavior of the static volume specific heat and dynamic thermal diffusivity, conductivity and effusivity of Cr2O3, around the Néel point, have been obtained. A comparison with similar investigations, obtained by using CuCrO2 (a solid thermoelectric materials) as a sensor, was performed. The results obtained with LTE as a sensor proved to be more accurate, due to the previously mentioned “perfect liquid sensor-solid sample” thermal contact.