Development of Thermal Conductivity Measurement System for Micro- Single Crystals of Molecular Compounds

Abstract

Development of a thermal conductivity measurement system designed for micro-size single crystals of molecular compounds is reported. This construction aims at measuring absolute values of thermal conductivity and its temperature dependence in a wide temperature range from 0.5 K to near room temperature. To investigate electronic states at low temperatures by this system, it is possible to measure thermal conductivity with external magnetic fields up to 10 T by using RuO2 thermometers. Furthermore, we describe a low-noise switching unit designed for this thermal conductivity measurement system, which allows smooth switching from RuO₂ thermometers for the low-temperature range to type-E thermocouple sensors for temperatures above 10 K without modifying sample set-up and connection of electronics. Using this extension of availability, we conducted an automated high-precision thermal conductivity measurement of small manganin rod-shaped samples for calibration. We also report analyses of the additional noises introduced by this switching system measured by the ac resistance bridge and thermocouples. Furthermore, we examined a method for correcting the effects of radiation heat loss which are inherent to the steady-state measurements typically performed above 150K effectively. This research improves the feasibility of the thermal conductivity measurement over a wide temperature range for molecular compounds in which a variety of electronic states emerging with interesting phonon dynamics.