All electrical detection of thermal Hall angle by on-slab thermocouples

We propose a simple and reliable measurement method for the thermal Hall effect by the use of thermocouples fabricated directly on a target material. The thermal Hall angle has been typically characterized by measuring diagonal and off diagonal terms of the thermal conductivity tensor with manually attached bulk thermometers such as thermocouples and resistance temperature sensors. However, the presence of contact thermal resistance between the material and thermometers and the ambiguity of actual temperature information under a magnetic field hinder the quantitative evaluation of the thermal Hall angle. In this work, to characterize the temperature gradient with low contact thermal resistance, we deposit a thermoelectric NiCu thin film directly on the target materials, pattern it into a crossbar shape, and attach two Au wires at the hot and cold junctions to form a closed electrical circuit, i.e., an on-slab thermocouple. Owing to the ideal fourfold symmetry of the structure, we can determine the thermal Hall angle simply from the ratio of the measured thermoelectric voltages in the longitudinal (input) and transverse (output) directions for the on-slab thermocouples under the out-of-plane magnetic field. The measurements for the Co2MnGa Heusler alloy and Ni slabs by the proposed method find that the thermal Hall effect was clearly detected in a wide temperature range from 60 to 330 K, which is quantitatively consistent with the literature. This approach offers a simple and reliable route to investigate the thermal Hall effect and reveal the wide variety of carrier transport and thermal conversion phenomena.