An evaluation of methods for measuring thermomagnetic transport properties of bulk and thin film materials

In the “method of four coefficients,” experimental data for electrical conductivity, Seebeck, Hall, and Nernst coefficients are fit to models based on Boltzmann transport theory to estimate quantities such as the carrier effective mass, concentration, mobility, and scattering exponent. This powerful method provides experimental information about the electronic structure and charge carrier scattering mechanisms in solids, and has been used to understand enhanced performance in some thermoelectric materials. Nevertheless, there is relatively little literature available regarding descriptions of experimental apparatuses and methods of measurement of all four coefficients on a single sample in a single measurement cycle. We recently constructed a custom system for measurement of thermomagnetic properties from 8 K to 400 K. Here we report on a study of different approaches for experimentally measuring these four coefficients on both bulk and thin films samples. For example, we have investigated the effect of mounting the sample in a flat vs. vertical geometry, which can be important for adiabatic vs. isothermal Nernst measurements. Our results provide useful guidance for constructing such apparatuses to measure the thermomagnetic properties used in the method of four coefficients.