Stray-fields based features observed for low and high magnetic fields in Ni$_{80}$Fe$_{20}$-Nb-Ni$_{80}$Fe$_{20}$ trilayers

TL;DR

This study investigates how stray magnetic fields influence the transport and magnetic properties of NiFe-Nb-NiFe trilayers at low and high magnetic fields, revealing the role of stray fields in magnetoresistance and superconducting behavior.

Contribution

It demonstrates the impact of transverse stray fields on low-field transport properties and proposes a general condition for strong magnetoresistance effects in trilayers.

Findings

Stray fields affect the Nb interlayer's transport properties at low fields.

Coercive field alignment of outer layers enhances magnetoresistance.

Critical field suppression occurs at low magnetic fields.

Abstract

We report on the influence of stray fields for both low and high magnetic fields applied parallel to trilayers consisting of a low-T Nb interlayer and two outer Ni Fe layers having in-plane anisotropy. At low magnetic fields these trilayers exhibit a pronounced magnetoresistance effect. Its dynamic transport behavior is presented through detailed I-V characteristics. More importantly, the detailed evolution of the longitudinal and transverse magnetic components of the trilayers is presented from close to well below T . These data clearly show that below T and for low magnetic fields the transport properties of the Nb interlayer are influenced by transverse stray-fields that motivate subsequent transverse magnetic coupling of the outer Ni Fe layers. By generalizing this experimental finding we propose that the generic prerequisite for the occurrence of intense magnetoresistance effects in relative trilayers is that the coercive fields of the outer ferromagnetic layers should almost coincide since the simultaneous occurrence of magnetic domains all over their surface will promote a transverse magnetic coupling mediated by the accompanying transverse stray fields. Finally, the trilayer's upper-critical field exhibits a pronounced suppression for low magnetic fields indicative of a behavior, while for high values the conventional behavior is recovered. A similar process is observed in both Nb-Ni Fe bilayers and Nb single layers. However, significant qualitative and quantitative differences exist between these samples. Based on a mechanism that is motivated by longitudinal stray-fields existing exclusively in the high-field regime we propose a possible interpretation for this experimental finding.