Paramagnon drag in high thermoelectric figure of merit Li-doped MnTe.

ABSTRACT: Local thermal magnetization fluctuations in Li-doped MnTe are found to increase its thermopower ? strongly at temperatures up to 900 K. Below the Néel temperature (T N ~ 307 K), MnTe is antiferromagnetic, and magnon drag contributes ?md to the thermopower, which scales as ~T 3. Magnon drag persists into the paramagnetic state up to >3 × T N because of long-lived, short-range antiferromagnet-like fluctuations (paramagnons) shown by neutron spectroscopy to exist in the paramagnetic state. The paramagnon lifetime is longer than the charge carrier-magnon interaction time; its spin-spin spatial correlation length is larger than the free-carrier effective Bohr radius and de Broglie wavelength. Thus, to itinerant carriers, paramagnons look like magnons and give a paramagnon-drag thermopower. This contribution results in an optimally doped material having a thermoelectric figure of merit ZT > 1 at T > ~900 K, the first material with a technologically meaningful thermoelectric energy conversion efficiency from a spin-caloritronic effect.

SUBMITTER: Zheng Y 

PROVIDER: S-EPMC6744264 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature