Control of Superconductivity with a Single Ferromagnetic Layer in Niobium/Erbium Bilayers

Abstract

Superconducting spintronics in hybrid superconductor-ferromagnet (S-F) heterostructures provides an exciting potential new class of device. The prototypical super-spintronic device is the superconducting spin-valve, where the critical temperature, T c , of the S-layer can be controlled by the relative orientation of two (or more) F-layers. Here, we show that such control is also possible in a simple S/F bilayer. Using field history to set the remanent magnetic state of a thinEr layer, we demonstrate for a Nb/Er bilayer a high level of control of both T c and the shape of the resistive transition, R(T), to zero resistance. We are able to model the origin of the remanent magnetization, treating it as an increase in the effective exchange field of the ferromagnet and link this, using conventional S-F theory, to the suppression of T c . We observe stepped features in the R(T) which we argue is due to a fundamental interaction of superconductivity with inhomogeneous ferromagnetism, a phenomena currently lacking theoretical description. * g.burnell@leeds.ac.uk

Proximity effect in [Nb(1.5 nm)/Fe(x)]10/Nb(50 nm) superconductor/ferromagnet heterostructures

“…Similar steps were already observed in several works [ 19 , 30 , 49 – 50 ]. Up to now there exists no explanation of such steps except for cases related to different imperfections of the sample (e.g., thickness gradient, crystal inhomogeneity, or oxide at S/F interface) [ 19 , 30 , 49 – 50 ]. However, a detailed study of our systems using various structural methods allows us to exclude these cases.…”

“…This state is characterized by a ≈50% suppressed resistance and the absence of the Meissner effect. Similar steps were already observed in several works [19,30,49,50]. Up to now there exists no explanation of such steps except for cases related to different imperfections of the sample (e.g., thickness gradient, crystal inhomogeneity, or oxide at S/F interface) [19,30,49,50].…”

Сверхпроводящие Спиновые Вентили На Основе Спиральных Магнетиков

“…Такое переключение ориентации возможно, потому что в подобных структурах реализована кубическая кристаллическая решетка без центральной симметрии, что создает 4 эквивалентных направления магнитной спирали в MnSi типа (111). В кристаллических решетках гольмия и эрбия, использовавшихся в экспериментах [15,21,28], подобного не наблюдается, так как пленки Ho обладают сильной магнитной анизотропией, что предотвращает существование эквивалентных спиральных направлений, поэтому они не являются лучшим выбором при конструировании сверхпроводниковой памяти.…”

Gauge theory of the long-range proximity effect and spontaneous currents in superconducting heterostructures with strong ferromagnets

“…1. Recently the proximity effect in helical magnets has been observed experimentally [55,56]. In this case the magnetization texture is described by h = h(cos α, sin α cos θ, sin α sin θ ), where we assume that the angle α is spatially independent and θ = θ (x).…”