Magnetic insulators (MIs) carry magnetic moments without charge dissipation, making them attractive for spintronic applications and proximity-effect-mediated superconducting device engineering, particularly at cryogenic temperatures. However, only a limited number of MI materials can be deposited as thin films on Si/SiOx substrates and processed using standard lithographic techniques. EuS is a promising MI that exhibits stable and reproducible magnetic properties even in polycrystalline thin films. This makes it a strong candidate for integration into low-temperature spintronic and superconducting devices. We have characterized the magnonic properties of EuS thin films at low temperatures, extracting a Gilbert damping on the order of 10⁻³ at 2 K in polycrystalline samples (1,2). This low damping highlights the potential of EuS for coherent magnonic experiments at cryogenic temperatures. In heavy metal/EuS heterostructures, we demonstrate spin injection and propagation through EuS films via the spin Seebeck effect (1). Furthermore, EuS proves to be an excellent material for inducing magnetic proximity effects in BCS superconductors such as Al. In particular, we investigate the transport properties of EuS/Al/AlOx/Al junctions, where we observe both the Josephson effect and multiple Andreev reflections (3). Overall, our results establish EuS as a versatile magnetic insulator platform for cryogenic spintronics and superconducting transport studies.
1) M. Xochitl Aguilar-Pujol, S. Catalano et al., Phys. Rev. B 108 (2023) 224420
2) M. Xochitl Aguilar-Pujol, S. Catalano et al., submitted to Phys. Rev. Mat.
3) D. Caldevilla, G. O. Steffensen, S. Catalano et al., accepted in Phys. Rev. Lett