Detection of thermoelectric effects in magnetic metals by ac higher harmonics technique*

Thermoelectric effects refer to the conversion of a temperature gradient into an electric signal in magnetic conductors. Anomalous Nernst effect (ANE) and anisotropic Seebeck Effect are thermoelectric effects that has been receiving increasing attention due to the development of spin caloritronics and topological material studies. In the measurements, external heater is the most common source of temperature gradient. We present an ac higher harmonics technique to detect thermoelectric effects in metal lines with temperature gradient induced by self-heating. We show that in Ni film, by Joule heating, it is possible to observe longitudinal and transverse thermoelectric effect in the second harmonics, separate from present longitudinal magnetoresistance signal, by using a lock-in detection technique with a circuit bridge. 3ω signals can be used to identify the heating. Besides film samples, our technique can also be applied to focus ion beam microfabricated element from bulk crystal. The ac higher harmonics technique provides a new path to probe the ANE in ferromagnets and anisotropic Seebeck Effect in antiferromagnets, promoting the application of spintronics devices.