The effect of manganese incorporation in Bi2Se3 on the thermal, electrical transport and magnetic properties

Abstract

Thermal, electrical transport, and magnetic measurements have been made on polycrystalline Mnx(Bi2Se3) where Mn was incorporated by melting Mn metal with pre-synthesized Bi2Se3. We find that, unlike Cux(Bi2Se3), this process leads to significant partial substitution of the 3d transition metal ion onto the Bi site rather than the interstitial site in the van der Waals gaps. Mn incorporation led to a systematic reduction in the magnitude of the thermopower and an increase in phonon scattering that resulted in a decrease in the thermal conductivity. The electronic contribution to the thermal conductivity at 300 K is 0.51 W m−1 K−1 for pure Bi2Se3, 0.75 W m−1 K−1 for the 3% Mn sample, but only 0.07 W m−1 K−1 for the 6% Mn incorporated sample. We find that the thermoelectric figure of merit, ZT, is enhanced in the 3% Mn sample by a factor of 1.7 at 300 K and a factor of 1.2 at 200 K. The pure compound has a susceptibility that can be modeled in terms of antiferromagnetic exchange between 0.13% half-filled (single electron) Se vacancies. Mn incorporation does not lead to magnetic order but there are antiferromagnetic interactions that become weaker with increasing Mn concentration. A positive power-law magnetoresistance is observed and it reaches 5.2% at low temperatures for the 3% Mn sample. The magnetoresistance is likely to arise from a Lorentz force effect. A lower magnetoresistance is measured for the 6% Mn sample and attributed to a shorter carrier mean free path from Mn impurity scattering.