Coexistence of the quantum anomalous Hall and anomalous Nernst effects in Cr-doped NaMgX (X = P, As, Sb) monolayers

Abstract

The integration of both the quantum anomalous Hall effect (QAHE) and the anomalous Nernst effect (ANE) into a single material system is critical yet remains a significant challenge for the advancement of multifunctional quantum devices. Herein, based on first-principles calculations, we predict that Cr-doped NaMgX (X = P, As, Sb) monolayers constitute a promising multifunctional platform for the simultaneous realization of both effects. The monolayers demonstrate robust structural, dynamic, and thermal stability—as evidenced by cohesive energy calculations, phonon spectra, and AIMD simulations—alongside high Curie-temperature (T_C) ferromagnetism that remains insensitive to Hubbard U variations. Our analysis reveals that Na₁₂Mg₁₀Cr₂X₁₂ monolayers behave as 100% spin-polarized Weyl semimetals and maintain their topological stability under strain in the absence of spin–orbit coupling (SOC). Upon the introduction of SOC, the ferromagnetic Weyl semimetal phase undergoes a transition into a ferromagnetic topological insulator, characterized by a Chern number |C| = 1, well-defined chiral edge states, and a quantized Hall conductivity plateau. Notably, substantial anomalous Nernst coefficients are achieved, peaking at 6.02 A (m K)⁻¹ for Na₁₂Mg₁₀Cr₂As₁₂ at 50 K. These findings establish Cr-doped NaMgX monolayers as a versatile platform hosting concurrent QAHE and ANE, paving the way for integrated, low-power microelectronic and thermal energy conversion devices.