Magnetotransport properties of magnetically soft spin-valve structures (invited)

TLDR

The study examines magnetotransport in soft ferromagnetic/nonmagnetic multilayers, where Ni, Co, and NiFe layers separated by Cu, Ag, or Au exhibit large low‑field resistance changes. One ferromagnet was pinned by exchange anisotropy (e.g., NiFe/FeMn) to vary the relative magnetization orientation. Room‑temperature ΔR/R reached 4.1 % in 10 Oe for a NiFe/Cu/NiFe/FeMn stack and 8.7 % in 20 Oe for a Co/Cu/Co stack; magnetoresistance peaks near 80 Å ferromagnetic thickness, decreases exponentially with Cu/Au interlayer thickness, and shows distinct Ag‑interlayer behavior, indicating bulk spin‑dependent scattering dominates over interfacial effects.

Abstract

The magnetic and magnetotransport properties of several series of sandwiches consisting of two ferromagnetic layers (Ni, Co, Ni80Fe20) separated by a noble metal (Cu, Ag, Au) are described. In order to vary the relative orientation of the magnetizations of the two ferromagnets, one of them was constrained by exchange anisotropy (e.g., NiFe/Fe50Mn50). The ferromagnetic layers are magnetically soft and not coupled antiparallel, giving very large changes of resistance at low fields. At room temperature relative changes ΔR/R of 4.1% in 10 Oe for Si/Ta 50 Å/NiFe 62 Å/Cu 22 Å/NiFe 40 Å/FeMn 70 Å/Ta 50 Å and 8.7% in 20 Oe has been obtained for a structure based on Co/Cu/Co layers. The magnetoresistance versus the thickness of the ferromagnetic layer shows a broad peak near 80 Å for Ni, Co and NiFe, demonstrating the importance of bulk rather than interfacial spin-dependent scattering, in contrast to Fe/Cr multilayers. The magnetoresistance decreases exponentially with increasing interlayer (Cu and Au) thickness, indicating that the magnetoresistance is due to the exchange of polarized electrons from one ferromagnetic layer to the other. The variation with Ag interlayer thickness is different for structural reasons.