Exploiting bi-modulated magnetic field and drive current modulation to achieve high-sensitivity Hall measurements on thermoelectric samples

Hall mobility measurements of samples with high carrier density are challenging due to the low Hall voltage. Increasing the drive current enhances the Hall voltage, but risks Joule heating at the contacts resulting in unreliable measurements. Measurement noise suppression can be achieved by modulating either the magnetic field or the drive current during the Hall measurement. The Parallel dipole line (PDL) AC Hall measurement technique is a very practical way to realize pure harmonic magnetic field modulation in a very compact design using rotating permanent magnets. In this work, we combine magnetic field modulation with alternating polarity drive current, i.e., using a simultaneous two-parameter modulation at very different frequencies to gain further noise reduction. It makes possible to determine the charge carrier mobility in materials featuring very high free carrier density (over 1 E21 cm⁻³). The reliability and the applicability of the bi-modulation method was tested on Sn doped NbCoSb thermoelectric samples. The results exhibited excellent sensitivity to the chemical composition of the samples and therefore proven to be an efficient method for the development of such materials. Graphical abstract: [Figure not available: see fulltext.]