Negative spin-valve effect in ${\mathrm{Co}}_{65}$${\mathrm{Fe}}_{35}$/Ag/${\left({\mathrm{Co}}_{65}{\mathrm{Fe}}_{35}\right)}_{50}$${\mathrm{Gd}}_{50}$ trilayers

A minimum of the magnetoresistance under low fields has been observed with a ${\mathrm{Co}}_{65}$${\mathrm{Fe}}_{35}$/Ag/${\left({\mathrm{Co}}_{65}{\mathrm{Fe}}_{35}\right)}_{50}$${\mathrm{Gd}}_{50}$ trilayer at 4.2 and 300 K. This negative spin-valve effect is explained by the scattering of the conduction electrons by the Co or Fe moments included in two different structures: a polycrystalline (${\mathrm{Co}}_{65}$${\mathrm{Fe}}_{35}$) and an amorphous one [${\left({\mathrm{Co}}_{65}{\mathrm{Fe}}_{35}\right)}_{50}$${\mathrm{Gd}}_{50}$]. The Gd moments allow one to control the magnetic configuration of the transition-metal moments of the layers but are inefficient for the magnetoresistance. This interpretation is confirmed by measurements using high pulsed fields.