CHANGE IN CONDUCTANCE IS THE FUNDAMENTAL MEASURE OF SPIN-VALVE MAGNETORESISTANCE

The absolute change of sheet conductance (DELTAG) 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 DELTAR/R or DELTAR, DELTAG 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 angstrom/Cu 25 angstrom/NiFe 50 angstrom/FeMn 90 angstrom/Ta 50 angstrom/Cu t(Cu)/Ta 50 angstrom, in which only the thickness t(Cu) is varied, the values and the thermal variations of DELTAR/R(T) and DELTAR(T) are strongly influenced by t(Cu) through its shunting effect. In contrast DELTAG is found to be independent of shunting.