Theory of superconducting and magnetic proximity effect in S$\mid$F structures with inhomogeneous magnetization textures and spin-active interfaces

TL;DR

This paper develops a comprehensive numerical theory for the superconducting and magnetic proximity effects in superconductor-ferromagnet structures, considering inhomogeneous magnetization textures and spin-active interfaces, with implications for experimental long-range triplet correlations.

Contribution

It introduces a numerical approach that includes spin-dependent interfacial phase shifts and inhomogeneous magnetization textures, advancing understanding of proximity effects in realistic S|F structures.

Findings

Bloch and Néel domain walls influence superconducting correlations.

Conical ferromagnets can sustain long-range triplet correlations.

Spin-DIPS can cause anti-screening of induced magnetization.

Abstract

We present a study of the proximity effect and the inverse proximity effect in a superconductor$\mid$ferromagnet bilayer, taking into account several important factors which mostly have been ignored in the literature so far. These include spin-dependent interfacial phase shifts (spin-DIPS) and inhomogeneous textures of the magnetization in the ferromagnetic layer, both of which are expected to be present in real experimental samples. Our approach is numerical, allowing us to access the full proximity effect regime. In Part I of this work, we study the superconducting proximity effect and the resulting local density of states in an inhomogeneous ferromagnet with a non-trivial magnetic texture. Our two main results in Part I are a study of how Bloch and N\'eel domain walls affect the proximity-induced superconducting correlations and a study of the superconducting proximity effect in a conical ferromagnet. The latter topic should be relevant for the ferromagnet Ho, which was recently used in an experiment to demonstrate the possibility to generate and sustain long-range triplet superconducting correlations. In Part II of this work, we investigate the inverse proximity effect with emphasis on the induced magnetization in the superconducting region as a result of the "leakage" from the ferromagnetic region. It is shown that the presence of spin-DIPS modify conclusions obtained previously in the literature with regard to the induced magnetization in the superconducting region. In particular, we find that the spin-DIPS can trigger an anti-screening effect of the magnetization, leading to an induced magnetization in the superconducting region with \textit{the same sign} as in the proximity ferromagnet.