Proximity effects in superconductor-ferromagnet heterostructures

TL;DR

This paper reviews the proximity effect in superconductor-ferromagnet heterostructures, highlighting oscillatory behavior of Cooper pairs, effects on critical temperature, and phenomena like domain-wall superconductivity, supported by recent experimental progress.

Contribution

It provides a unified theoretical description of proximity effects in superconductor-ferromagnet systems and discusses recent experimental observations of related phenomena.

Findings

Oscillatory behavior of Cooper pairs in ferromagnets.

Non-monotonous dependence of critical temperature on ferromagnetic layer thickness.

Observation of domain-wall superconductivity.

Abstract

The very special characteristic of the proximity effect in superconductor-ferromagnet systems is the damped oscillatory behavior of the Cooper pair wave function in a ferromagnet. In some sense, this is analogous to the inhomogeneous superconductivity, predicted long time ago by Larkin and Ovchinnikov (1964), and Fulde and Ferrell (1964), and constantly searched since that. After the qualitative analysis of the peculiarities of the proximity effect in the presence of the exchange field, the author provides a unified description of the properties of the superconductor-ferromagnet heterostructures. Special attention is paid to the striking non-monotonous dependance of the critical temperature of the multilayers and bilayers on the ferromagnetic layer thickness and conditions of the realization of the "Pi"- Josephson junctions. The recent progress in the preparation of the high quality hybrid systems permitted to observe on experiments many interesting effects, which are also discussed in the article. Finally, the author analyzes the phenomenon of the domain-wall superconductivity and the influence of superconductivity on the magnetic structure in superconductor-ferromagnet bilayers.