Thermopower and Self-consistent Spin-Wave Theory for MnTe

The experimental data indicate that thermopower increases dramatically due to magnon drag in antiferromagnetic Li-doped MnTe near the Néel temperature (T_N). Also, thermopower sustains its high magnitude in temperatures above T_N where a lack of magnons is expected. This behavior seems to exist due to the presence of short-range order (SRO) and correlation. Therefore, we calculated the thermopower versus temperature near and above T_N by investigating magnetic order and correlation. The spin-wave theory (SWT) works well in magnetic materials at low temperatures, unlike at high temperatures where the theory fails to describe the SRO and correlations. To date, different approaches have been used for 2D, quasi 2D, and 3D systems such as variational method, boson mean-field theory, and modified SWT based on Dayson-Maleev representation for spin operators, all of which fail to provide the correct value of ordering temperature and behavior estimation near and above the T_N. We show that considering the Baryakhtar-Krivoruchko-Jabelonski representation via bosons and pseudofermions in self-consistent SWT can describe the SRO above T_N. The theoretical results are presented and benchmarked against the experimental data to justify the high-temperature thermopower.