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 α strongly at temperatures up to 900 K. Below the Néel temperature (TN ~ 307 K), MnTe is antiferromagnetic, and magnon drag contributes αmd to the thermopower, which scales as ~T3. Magnon drag persists into the paramagnetic state up to >3 × TN 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.

Largely Suppressed Magneto-Thermal Conductivity and Enhanced Magneto-Thermoelectric Properties in PtSn 4

“…These results on PtSn 4 provide a paradigm for tuning highly conductive semimetals for both longitudinal and transverse thermoelectric conversion by applying a magnetic field. Interestingly, some recent work had paid attention to the relationship between thermoelectric performance and internal magnetic interactions, for example, superparamagnetic behavior [45], paramagnon drag [46], and spin fluctuation [47]. These works together with our current study on PtSn 4 demonstrate that introducing magnetic interaction as an additional influence on the transport properties, either by applying an external magnetic field or by introducing an internal magnetic moment, could open a new direction in thermoelectric research.…”

Thermoelectric, Magnetic, and Mechanical Characteristics of Antiferromagnetic Manganese Telluride Reinforced with Graphene Nanoplates

“…However, the spindisorder scattering in MnTe is in the range of a few tens of femtoseconds. [33] GNP addition will add more interface scattering to the material, although such defect scatterings are in the picosecond ranges and will not affect the carrier mobility significantly.…”

“…Along with discovering novel TE compounds and the continued interest in developing efficient chalcogenide TE materials, [27][28][29][30][31][32] lead-free MnTe, an antiferromagnetic (AFM) transition metal-semiconductor, has shown potential as an efficient TE material. [33,34] This material has been investigated since the late 1930s [35,36] as either undoped [37][38][39][40] or doped compounds such as MnTeLi, [38] (GeTe) 1Àx (MnTe) x , [41,42] (Ge, Pb) 1Àx Mn x Te, [43] Cd 1Àx Mn x Te, [44] Sn 1Àx Mn x Te, [45] and Zn 1Àx Mn x Te. [46] MnTe has a Néel temperature (T N ) of 307-310 K [47,48] and a bandgap of 1.27 eV, [47,49,50] with a high Seebeck coefficient (%450 μV K À1 ) [49,51] and spin-wave excitation (magnon) drag effect.…”

“…[46] MnTe has a Néel temperature (T N ) of 307-310 K [47,48] and a bandgap of 1.27 eV, [47,49,50] with a high Seebeck coefficient (%450 μV K À1 ) [49,51] and spin-wave excitation (magnon) drag effect. [33,34] Also, in contrast to other manganese chalcogenides such as MnO, MnS, and MnSe, which form with a cubic NaCl-type crystal structure, MnTe has a hexagonal NiA-type crystal structure in its ground state. [49] However, MnTe suffers from two properties, mainly low electrical conductivity and chemical instability, which can compromise its potential application as an efficient TE material.…”

Anomalous Thermopower and High ZT in GeMnTe 2 Driven by Spin’s Thermodynamic Entropy

“…For this reason, the theory does not tell us how to tune the spin entropy under finite temperature. Recently, the Seebeck coefficient in Li-doped MnTe was found to be significantly enhanced by the magnetic phase transition, while the enhancement is strongly dependent on the transition temperature and carrier concentration [ 36 – 38 ]. The phenomenon was explained by magnon (or paramagnon) drag, but not spin entropy.…”