Phys. Rev. Lett. 113, 027601 (2014)

A temperature difference between two metals in contact generates a voltage — the Seebeck effect. The opposite phenomenon, known as the Peltier effect, implies heating or cooling at the interface of such a junction when an electric current flows through it. The two processes are Onsager reciprocals, as they obey the reciprocal relations derived by Lars Onsager for irreversible thermodynamic processes.

Now, similar thermoelectric effects for spin currents are being explored. Following the discovery of the spin Seebeck effect at the interface between a magnetic insulator and a metal, Joost Flipse and colleagues now report its Onsager reciprocal, the spin Peltier effect.

The authors' device consists of a platinum film grown on top of Y3Fe5O12 (yttrium iron garnet, an insulating ferrimagnet). A charge current through the platinum layer, in combination with an external magnetic field, results in spin accumulation at the interface — the spin Hall effect. This spin build-up is picked up by the magnetic insulator and converted into magnons (collective excitations of the crystal lattice's spin structure). Heat is transferred from the electrons in the platinum film to the magnons — or vice versa, depending on the direction of the magnetization in Y3Fe5O12.