SLS: Magnon-Drag as a Pathway to High-Efficiency Thermoelectric Metals

Sarah Watzman, PhD Candidate, Mechanical Engineering

All dates for this event occur in the past.

E525 Scott Lab
E525 Scott Lab
201 W. 19th Ave.
Columbus, OH 43210
United States

The majority of the world’s energy comes from nonrenewable sources, with nearly 60% of this energy being rejected as waste-heat.  If this waste-heat could be recovered, this would have an effect on humanity equivalent to that of adding a renewable energy source to the system.  One manner in which to do this is utilizing thermoelectric materials, which convert heat to electricity.  When n-type and p-type thermoelectric materials are paired electrically in series between a heat source (waste-heat) and the ambient, a temperature gradient across the couples is induced which is then converted into a usable voltage output via the Seebeck Effect.  Typical thermoelectric materials are semiconductors, which are expensive, brittle, and difficult to form or connect.  Comparatively, metals are cheap, strong, and easy to form or connect.  Unfortunately, metals typically have a low thermoelectric efficiency.  In this work, we explore magnon-drag as a mechanism to enhance the thermoelectric efficiency of metals.  Magnon-drag is advective transport that utilizes magnetization dynamics in a temperature gradient to pull charge carriers through a crystal lattice.  It is thus present in ferromagnets such as iron, cobalt, nickel, and many of their alloys.  We experimentally determine the temperature dependence of thermopower, which characterizes the conversion of a temperature gradient into a voltage in a thermoelectric material, in elemental iron, cobalt, and nickel and illustrate how the effect is impervious to defects.  We develop a macroscopic hydrodynamic model to quantify the magnon-drag contribution to metallic thermopower and compare this to our experimental results, which show magnon-drag does dominate the thermopower of elemental metals over given temperature ranges.  This offers a predicative formula for future work in developing new, high-efficiency thermoelectric alloys.