Purley Peltier: Making YIG cool again

This week its back to the much loved Pt/YIG system, but not for Spin Hall magnetoresistance measurements, rather for measurements of the spin Peltier effect (SPE).  The SPE is the Onsager reciprocal of the spin Seebeck effect (SSE), and is the generation of a magnon heat current in a magnetic insulator by a spin current at the interface with a metal.  In this paper, the spin current in the Pt layer is experimentally realised by the spin Hall effect.  The spin current transfers spin angular momentum with magnons in the YIG at the interface, and the direction of the transfer of the spin angular momentum depends on the relative orientations of the spin magnetic moment in the Pt and the magnetization of the YIG.  This change of angular momentum of the magnons generates a temperature difference between the magnons and phonons in the YIG, and so through magnon-phonon scattering this temperature difference is relaxed by lattice cooling or heating.  Experimentally the SPE is observed by processing a device where thermopile are places near the Pt/YIG interface.  The first harmonic voltage measured across the thermopile switches as the magnetization in the YIG switches with an external magnetic field, and the use of thermal modelling reveals that the measured voltage difference corresponds to a temperature difference of 0.25mK at the thermopile, 39% of the value at the interface itself.  The data and thermal modelling of the SPE and SSE confirm their reciprocity.

Image: @Doug88888,CC BY-NC-SA 2.0