Phase diagram of a superconductor / ferromagnet bilayer

TL;DR

This paper explores how ferromagnetic domain structures influence the phase diagram of a superconductor, revealing significant modifications in critical temperature and critical field behavior due to inhomogeneous stray fields.

Contribution

It provides a detailed analysis of the impact of different ferromagnetic domain configurations on the superconductor's phase diagram, highlighting new effects like asymmetry and dimensional crossover.

Findings

Band-like domains reduce Tc and increase the slope of Hc2(T).

Bubble domains cause asymmetric phase boundaries due to field compensation.

Inhomogeneous domains induce a crossover from 1D to 2D superconducting behavior.

Abstract

The magnetic field (H) - temperature (T) phase diagram of a superconductor is significantly altered when domains are present in an underlying ferromagnet with perpendicular magnetic anisotropy. When the domains have a band-like shape, the critical temperature Tc of the superconductor in zero field is strongly reduced, and the slope of the upper critical field as a function of T is increased by a factor of 2.4 due to the inhomogeneous stray fields of the domains. Field compensation effects can cause an asymmetric phase boundary with respect to H when the ferromagnet contains bubble domains. For a very inhomogeneous domain structure, Tc~H^2 for low H and Tc~H for higher fields, indicating a dimensional crossover from a one-dimensional network-like to a two-dimensional behavior in the nucleation of superconductivity.