Large Tunable Thermoelectric Effects in Superconducting Spin Valves with Commercially Available Materials

P. Tuero, J.B. Tjernshaugen, C. Sánchez, C. González-Ruano, Y. Lu, J. Linder, F. Aliev Kazanski

PRX Energy Vol. 4, nº. 3, pp. 033003

Summary:

Recent studies have revealed magnetically controllable thermoelectric effects in superconductor/ferromagnet (S/F) structures. A tunable cryogenic thermoelectric generator needs not only a high conversion factor between electricity and heat, but also a large change in the thermoelectric output when switching the magnetic state of the device. However, the reported modifications in thermoelectric power are either minimal, involve superconductors with relatively low critical temperatures (below 1 K), or do not utilize commercially available spintronic materials. Here, we experimentally measure and numerically model thermoelectric effects in fully epitaxial ferromagnet/superconductor/ferromagnet (F/S/F) junctions based on commercially available easily grown materials, as well as their dependence on the magnetic configuration of the ferromagnetic (F) electrodes. We observe sizeable Seebeck coefficients for the parallel alignment of the F electrodes, reaching values of about 100 µV/K. Importantly, we find a decrease of the thermoelectric signal of more than an order of magnitude when switching from a parallel to an antiparallel configuration, constituting a large thermoelectric spin-valve effect. Theoretical modeling based on a self-consistent nonequilibrium Keldysh-Usadel Green's function theory, combined with micromagnetic simulations, qualitatively reproduce the experimental findings. The thermoelectric effect is optimized when there is a large spin-dependent electron-hole asymmetry in the superconductor combined with spin-dependent transmission through the interfaces. These findings pave the way for the development of efficient and versatile cryogenic thermoelectric heat engines.

Spanish layman's summary:

El trabajo demuestra que dispositivos ferromagneto/superconductor pueden generar electricidad a partir del calor de forma controlable magnéticamente. Usando materiales comerciales, logran una señal termoeléctrica alta que cambia drásticamente al modificar la orientación magnética, útil para generadores criogénicos eficientes.

English layman's summary:

This work shows that ferromagnet/superconducting devices can generate electricity from heat in a magnetically controllable way. Using commercial materials, they achieve a high thermoelectric signal that changes dramatically by modifying the magnetic orientation, which is useful for efficient cryogenic generators.

Keywords: Electrical conductivity; Electrical properties; Magnetism; Micromagnetism; Spintronics; Superconductivity; Thermoelectrics

DOI reference: https://doi.org/10.1103/xbgg-gttc

Published on paper: September 2025.

Published on-line: July 2025.

Citation:
P. Tuero, J.B. Tjernshaugen, C. Sánchez, C. González-Ruano, Y. Lu, J. Linder, F. Aliev Kazanski, "Large Tunable Thermoelectric Effects in Superconducting Spin Valves with Commercially Available Materials", PRX Energy, Vol. 4, nº. 3, pp. 033003, September 2025. [Online: July 2025] doi: 10.1103/xbgg-gttc