Synergy of exchange bias with superconductivity in ferromagnetic-superconducting layered hybrids: the influence of in-plane and out-of-plane magnetic order on superconductivity

TL;DR

This study explores how exchange bias and magnetic order influence superconductivity in ferromagnetic-superconducting hybrids, revealing that magnetic coupling and stray fields can enhance or suppress superconductivity depending on magnetic configuration.

Contribution

It provides a systematic analysis of magnetic and transport behaviors in FM-SC hybrids, highlighting the role of magnetic coupling and stray fields in superconductivity modulation.

Findings

Magnetic coupling affects superconductivity in FM-SC hybrids.

Stray fields from multidomain states influence superconducting properties.

Exchange bias can either promote or suppress superconductivity.

Abstract

It is generally believed that superconductivity and magnetism are two antagonistic long-range phenomena. However, as it was preliminarily highlighted in D. Stamopoulos et al. [Phys. Rev. B 75, 014501 (2007)] and extensively studied in this work under specific circumstances these phenomena instead of being detrimental to each other may even become cooperative so that their synergy may promote the superconducting properties of a hybrid structure. Here, we have studied systematically the magnetic and transport behavior of such exchange biased hybrids that are comprised of ferromagnetic (FM) Ni80Fe20 and low-Tc superconducting (SC) Nb for the case where the magnetic field is applied parallel to the specimens. Two structures have been studied: FM-SC-FM trilayers (TLs) and FM-SC bilayers (BLs). Detailed magnetization data on the longitudinal and transverse magnetic components are presented for both the normal and superconducting states. These data are compared to systematic transport measurements including I-V characteristics. The comparison of the exchange biased BLs and TLs that are studied here with the plain ones studied in D. Stamopoulos et al. [Phys. Rev. B 75, 184504 (2007)] enable us to reveal an underlying parameter that may falsify the interpretation of the transport properties of relevant FM-SC-FM TLs and FM-SC BLs investigated in the recent literature: the underlying mechanism motivating the extreme magnetoresistance peaks in the TLs relates to the suppression of superconductivity mainly due to the magnetic coupling of the two FM layers as the out-of-plane rotation of their magnetizations takes place across the coercive field where stray fields emerge in their whole surface owing to the multidomain magnetic state that they acquire.