Superconducting state of very thin Pd films deposited on a diluted insulating EuxSr1-xS ferromagnet

Abstract

The electronic transport in very thin Pd films deposited on insulating EuxSr1-xS (0 <= x <= 1) is investigated. The temperature dependent resistance R(T) of films with d(Pd) >= 14 nm shows metallic behavior and a logarithmic increase toward low temperatures characteristic of (anti-)localization and electron-electron interaction effects also observed for Pd films on Si(111). Films with d(Pd) = 7 nm are superconducting below a transition temperature T-c which decreases with increasing Eu concentration from T-c = 0.9 K for x = 0 to T-c < 50 mK for x = 1. The origin of superconductivity in the thin Pd films is presumably due to the formation of an interfacial Pd-S alloy and/or to a charge transfer at the Pd/EuxSr1-xS interface. The decrease of T-c vs x is attributed to the magnetic pair breaking of the ferromagnetic EuxSr1-xS underneath. The R(T) behavior of films with d(Pd) >= 10 nm suggests that these are not superconducting or have a strongly reduced Tc presumably due to the proximity effect of the nonsuperconducting S-free upper part of the Pd film.