Ab-initio Prediction of Gigantic Anomalous Nernst Effect in Ferromagnetic Monolayer Transition Metal Trihalides

The anomalous Hall conductivity of all transition metal trihalides was explored using first-principles calculations. Employing the Fukui-Hatsugai-Suzuki method, we found that ferromagnetic monolayers X Br 3 ( X = Pd, Pt) possessed the quantized anomalous Hall conductivity (QAHC) with and without carrier doping. Due to unique QAHC, their transverse thermoelectric properties of X Br 3 ( X = Pd, Pt) were investigated. Employing the semi-classical Boltzmann transport theory, the transverse thermoelectric coefficient of each monolayer was analyzed. Anomalous Nernst coefficients (ANCs) of the X Br 3 monolayers were prominent both at and near the Fermi level. Under an assumed relaxation time of 10 fs, the maximum ANCs for the PdBr 3 (PtBr 3 ) monolayer reached −54.1 (−23.3) µ V K −1 at T = 300 K upon doping with 1.21 × 10 14 (5.64 × 10 13 ) holes cm −2 . The large ANCs of the X Br 3 monolayers were attributed to the opening of a narrow bandgap generated by spin–orbit coupling both at and near the Fermi level, which led to a large Seebeck-induced charge current and large anomalous Nernst conductivity. These results suggest that ferromagnetic X Br 3 monolayers have significant potential for application in thermoelectric devices.