Quantitative noncontact measurement of thermal Hall angle and transverse thermal conductivity by lock-in thermography

We propose and demonstrate a quantitative noncontact measurement method for the thermal Hall effect (THE) based on magnetic-field-modulated lock-in thermography. This method enables visualization of THE-induced temperature change and quantitative estimation of the thermal Hall angle ${\theta }_{\mathrm{T}\mathrm{H}\mathrm{E}}$ by applying periodic magnetic fields to a sample and obtaining the first harmonic response of thermal images. By combining this method with LIT-based measurement techniques for the longitudinal thermal conductivity ${\kappa }_{xx}$, we also quantify the transverse thermal conductivity ${\kappa }_{xy}$. We validate our measurement methods by estimating ${\theta }_{\mathrm{T}\mathrm{H}\mathrm{E}}$, ${\kappa }_{xx}$, and ${\kappa }_{xy}$ in a ferromagnetic Heusler alloy Co${}_2$MnGa slab showing large THE.