Change in conductance is the fundamental measure of spin-valve magnetoresistance

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Abstract
The absolute change of sheet conductance (ΔG) of spin-valve multilayers is shown analytically and experimentally to be the macroscopic observable most directly related to the physical mechanism of giant magnetoresistance. Unlike the changes in resistance ΔR/R or ΔR, ΔG is directly connected to the changes in the Fermi spheres of the ferromagnetic layers induced by the variation in magnetic alignment. In structures comprising Si/Co 80 Å/Cu 25 Å/NiFe 50 Å/FeMn 90 Å/Ta 50 Å/Cu tCu/Ta 50 Å, in which only the thickness tCu is varied, the values and the thermal variations of ΔR/R(T) and ΔR(T) are strongly influenced by tCu through its shunting effect. In contrast ΔG is found to be independent of shunting.