Sensor free, self regulating thermal switching via anomalous Ettingshausen effect and spin reorientation in DyCo5

Abstract

We propose a sensor free, self regulating thermal switch that combines the anomalous Ettingshausen effect (AEE) with a temperature driven spin reorientation transition (SRT) in the rare earth cobalt compound DyCo$_5$. Using density functional theory and the Kubo linear-response formalism, we compute the anomalous Hall conductivity $\sigma_{xy}(\varepsilon)$ and the finite temperature anomalous Nernst conductivity $\alpha_{xy}(T)$ for two magnetization directions, magnetization parallel and perpendicular to the crystallographic c axis. While the intrinsic $\sigma_{xy}$ at the Fermi level remains sizable for both orientations, $\alpha_{xy}$ exhibits an about two orders of magnitude contrast in the SRT temperature window. This contrast is consistent with the low temperature Mott relation through the energy slope $\partial_\varepsilon \sigma_{xy}(\varepsilon)\rvert_{E_{\mathrm F}}$ and is traced to strongly peaked Berry curvature hot spots generated by spin orbit coupling induced avoided crossings of Co $3d$ bands. Combining $\alpha_{xy}$ with longitudinal transport coefficients, we estimate device level metrics, namely the anomalous Nernst thermopower $S_{\mathrm{ANE}}$ and the Ettingshausen coefficient $\Pi_{\mathrm{AEE}}=T S_{\mathrm{ANE}}$, and demonstrate robust orientation controlled switching under a fixed in plane bias current. These results establish a materials based route to compact thermal control without external sensors or feedback electronics and provide a concrete example that the proposed principle can be realized in an existing ferromagnet.