Ettingshausen effect

The Ettingshausen effect (named for Albert von Ettingshausen) is a thermoelectric (or thermomagnetic) phenomenon that affects the electric current in a conductor when a magnetic field is present.[1]

Thermoelectric effect
Principles Thermoelectric effect Seebeck effect Peltier effect Thomson effect Seebeck coefficient Ettingshausen effect Nernst effect
Applications Thermoelectric materials Thermocouple Thermopile Thermoelectric cooling Thermoelectric generator Radioisotope thermoelectric generator Automotive thermoelectric generator

Ettingshausen and his PhD student Walther Nernst were studying the Hall effect in bismuth, and noticed an unexpected perpendicular current flow when one side of the sample was heated. This is also known as the Nernst effect. Conversely, when applying a current (along the y-axis) and a perpendicular magnetic field (along the z-axis) a temperature gradient appears along the x-axis. Because of the Hall effect, electrons are forced to move perpendicular to the applied current. Due to the accumulation of electrons on one side of the sample, the number of collisions increases and a heating of the material occurs. This effect is quantified by the Ettingshausen coefficient P, which is defined as:

${\displaystyle P={\frac {dT/dx}{|B_{z}|\cdot J_{y}}}}$

where dT/dx is the temperature gradient that results from the y-component J_y of an electric current density and the z-component B_z of a magnetic field.

temperature gradient due to Ettingshausen effect with applied magnetic field and electric current

In most metals like copper, silver and gold P is on the order of 10⁻¹⁶ Km/(TA) and thus difficult to observe in common magnetic fields. In bismuth the Ettingshausen coefficient is several orders of magnitude larger because of its poor thermal conductivity.

${\displaystyle P_{\mathrm {bismuth} }=7.5\pm 0.3\times 10^{-4}{\frac {K\cdot m}{T\cdot A}}}$[2]