Magnetoresistance in NiFe/Au multilayers and spin-valve structures (abstract)

Permalloy has been widely studied and used in industry for magnetic recording heads and sensors. This article presents a study of the magnetoresistance of (NiFe/Au)n multilayer films and NiFe/Au/NiFe sandwich structures. Gold is used as the spacer layer because of its low solid solubility in NiFe and the tendency of NiFe and Au to phase separate. Films were grown by dc sputtering with a series of different permalloy and Au thickness. In the multilayer films, the thickness of permalloy varies from 20 to 40 Å and Au varies from 8 to 25 Å. A difference in the sign and magnitude of magnetoresistance for transverse and longitudinal field directions with respect to current indicates the presence of anisotropic magnetoresistance (AMR) effect. The magnitude of Δρ/ρ is small because of shunting by Au layers. In the sandwich structures, the thickness of permalloy layers is different on each side of the Au and varies from 150 to 800 Å. The Au spacer layer varies from 20 to 60 Å. The measurements show mainly anisotropic magnetoresistance. There was a small opposite jump at ∼8 Oe on resistivity measurement, which indicates spin valve effect superimposed on the AMR effect. After annealing, the change in magnetoresistance is much more sensitive in low field ∼15 Oe, a property which is critical to many applications.