  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.
