Giant magnetoresistance of magnetically soft sandwiches: Dependence on temperature and on layer thicknesses

Abstract

We present comprehensive results on the magnetoresistive properties of spin-valve sandwiches comprising glass/M(1)/Cu/Ni80Fe20/Fe50Mn50/Cu, where M(1) is a ferromagnetic transition metal or alloy (Co,Ni,Ni80Fe20). We discuss the thermal variation of the magnetoresistance (R/R) and its dependence on the thicknesses of the layers constituting the active part of the spin-value sandwich [i.e., M(1)/Cu/NiFe]. An almost linear decrease of R/R is observed between 77 and 320 K. For a given ferromagnetic material, R/R extrapolates to zero at a temperature T0SV significantly lower than the Curie temperature, and independent of the ferromagnetic layer thickness. We have identified spin- and spin- intermixing by spin-wave scattering as responsible for the thermal decrease of the magnetoresistance. We show that the magnetoresistance arises within the active parts of the ferromagnetic layers of thickness of about 90 located next to the M/Cu interfaces. We give a phenomenological expression relating R/R to the longer of the two spin-dependent mean free paths, and to current shunting in the inactive part of the sandwich. The thickness of the active region is independent of temperature. © 1992 The American Physical Society.