Title: Long-range proximity effect in Nb-based heterostructures induced by a magnetically inhomogeneous permalloy layer,
Abstract: Odd-frequency triplet Cooper pairs are believed to be the carriers of
long-range superconducting correlations in ferromagnets. Such triplet pairs are
generated by inhomogeneous magnetism at the interface between a superconductor
(S) and a ferromagnet (F). So far, reproducible long-range effects were
reported only in complex layered structures designed to provide the magnetic
inhomogeneity. Here we show that spin triplet pair formation can be found in
simple unstructured Nb/Permalloy (Py = Ni_0.8Fe_0.2)/Nb trilayers and Nb/Py
bilayers, but only when the thickness of the ferromagnetic layer ranges between
140 and 250 nm. The effect is related to the emergence of an intrinsically
inhomogeneous magnetic state, which is a precursor of the well-known stripe
regime in Py that in our samples sets in at thickness larger than 300 nm.