# Control of superconductivity with a single ferromagnetic layer in niobium/erbium bilayers

## TL;DR

This paper demonstrates control over superconductivity in Nb/Er bilayers by manipulating the magnetic state of the ferromagnetic Er layer, affecting the critical temperature and transition shape, revealing new insights into S-F interactions.

## Contribution

It shows that a simple superconductor/ferromagnet bilayer can be controlled via remanent magnetization, expanding the understanding of superconducting spintronics beyond multi-layer devices.

## Key findings

- Control of T_c and R(T) shape via magnetic history in Nb/Er bilayers
- Modeling of remanent magnetization as an effective exchange field
- Observation of stepped R(T) features linked to inhomogeneous ferromagnetism

## 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 thin Er 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.