Controlling the electromagnetic proximity effect by tuning the mixing between superconducting and ferromagnetic order

Abstract

We present low-energy muon-spin rotation measurements on $\mathrm{Cu}/\mathrm{Nb}/{\mathrm{AlO}}_{x}/\mathrm{Co}$ thin films that probe the newly described electromagnetic (EM) proximity effect. By varying the thickness of the insulating ${\mathrm{AlO}}_{x}$ layer we control the degree of coupling between the superconductor and ferromagnet and thus the EM proximity effect. For barrier thicknesses up to 4 nm we find both a small contact-dependent reduction in the standard Meissner effect and a larger diamagnetic contribution originating at the $\mathrm{Nb}/{\mathrm{AlO}}_{x}/\mathrm{Co}$ interface which decays away over a lengthscale far exceeding the superconducting coherence length. This second component we attribute to the EM proximity effect. Our analysis provides compelling experimental evidence for previously neglected electromagnetic effects within proximity coupled systems.