Correlation between the magnetic and thermoelectric properties in Mg2−xMnxSi

• Single crystals of Mg2−xMnxSi were prepared by using a vertical Bridgman method.
• The thermoelectric performance was improved as doping Mn into Mg2Si.
• The magnetic properties were enhanced with Mn dopants.
• The thermoelectric and magnetic properties were strongly correlated in Mg2−xMnxSi.

Single crystals of Mg2−xMnxSi (x = 0, 0.1, 0.2, 0.3, and 0.4) were prepared using a vertical Bridgman method. The formation of desired materials was confirmed using single-crystal and powder X-ray diffraction. The thermoelectric and magnetic properties were investigated for various Mn contents in the temperature range between 2 and 300 K and in magnetic fields up to 70 kOe. For various x values, Mg2−xMnxSi with x = 0.2 possesses the highest figure of merit. The experimental results revealed that the substitutional Mn atoms exhibit mixed valences of +3 (majority) and +2, giving rise to dramatic changes of carrier density and magnetic interaction. At the same time, the Seebeck coefficient and magnetic susceptibility show a sudden change at the same temperature. These results imply that the thermoelectric properties are correlated with the magnetic properties in the Mg2−xMnxSi crystals.