Spin Effects Making zT > 1

Recent studies of thermoelectric properties of the antiferromagnetic MnTe:Li have revealed the existence of a strong spin effect that extends across a broad range of temperature leading to zT>1 [1,2]. While carrier mobility and heat capacity were strongly affected by spin contributions near the Neel temperature, T_N=307K, the thermopower demonstrated robust spin effects extending up to 900K. Spin contribution to those properties below T_N has been attributed to the magnon-drag effect [3]. A recent study [2] attributed the thermopower enhancement to paramagnon-drag effect originated from the mid or short-range magnetic ordering above T_N. Neutron scattering study showed an agreement to that theory to some extent while some competing theories such as the spin-fluctuations and spin entropy can also explain thermopower enhancement in magnetic materials [1,4]. The objective of this work is to show the agreements and disagreements of different spin-based theories in describing the transport properties of MnTe:Li and to compare similar material systems to gain better insight to the underlying physics.
[1] Vashaee, D., et al., Spin-Cal. IX, June 2018
[2] Yuanhua, Z., et al., Am. Phys. Soc., March 2018
[3] Wasscher, J. D., Phys. Lett. 8, 302-304,1964
[4] Gratz, E., Physica B 237-238, 1997