Effects of Ge Doping on Micromorphology of MnSi in MnSi ∼1.7 and on Their Thermoelectric Transport Properties

• Published in: Japanese Journal of Applied Physics 2005-12, Vol.44 (12R), p.8562
• Main Authors: Aoyama, Ikuto, Fedorov, Mikhail I., Zaitsev, Vladimir K., Solomkin, Fedor Yu, Eremin, Ivan S., Samunin, Aleksandr Yu, Mukoujima, Mika, Sano, Seijiro, Tsuji, Toshihide
• Format: Article
• Language: English
• ISSN: 0021-4922; 1347-4065
• DOI: 10.1143/JJAP.44.8562

MnSi layers in Ge-doped MnSi ∼1.7 increased with increasing Ge content up to x =0.00133, began to break at x =0.00265 and finally disappeared at x =0.00530. An experimental equation for the growth of MnSi was proposed for the interval between the MnSi layers and amount of doped Ge content. The crystallinity of Ge-doped MnSi ∼1.7 increased initially with increasing doped Ge content and saturated at high Ge content. Thermoelectric transport properties along the c -axis of Ge-doped MnSi ∼1.7 were measured as a function of Ge content at room temperature. Electrical conductivity and thermoelectric power of Ge-doped MnSi ∼1.7 were compared to those of Al-doped MnSi ∼1.7 in our previous work. A maximum in the electrical conductivity and a minimum in the thermoelectric power of Ge-doped MnSi ∼1.7 were observed at x =0.00133, reflecting a change in hole density which was influenced by the volume ratio of MnSi. Hole mobility depended on the existence of MnSi layers and/or of interfaces between MnSi ∼1.7 and MnSi and on the crystallinity of MnSi ∼1.7 . The thermal conductivity of Ge-doped MnSi ∼1.7 had a maximum at x =0.00053. The increase in thermal conductivity at low Ge doping can be explained by the increase in the amount of MnSi segregated in doped MnSi ∼1.7 , while the decrease at high Ge content was caused by the increase in phonon scattering of Ge. A maximum figure of merit of Ge-doped MnSi ∼1.7 was obtained at x =0.00974, reflecting a maximum power factor.