Search for mean-free-path effects in current-perpendicular-to-plane magnetoresistance

Abstract

We search for evidence of ``mean-free-path'' (mfp) effects in the current-perpendicular-to-plane (CPP) magnetoresistance (MR) of sputtered Co/Cu/Co, Co/Ag/Co, and Co/Au/Co exchange-biased spin-valves by examining how the quantity $\sqrt{{(AR}_{\mathrm{AP}})(A\ensuremath{\Delta}R)}$ decreases as only the thickness of the Cu, Ag, or Au layer is increased. Here ${\mathrm{AR}}_{\mathrm{AP}}$ is the specific resistance (area A times resistance R) of the exchange-biased spin-valve when the magnetizations of the pinned and unpinned Co layers are aligned antiparallel (AP) to each other, and $A\ensuremath{\Delta}{R=AR}_{\mathrm{AP}}\ensuremath{-}{\mathrm{AR}}_{P}$ is the difference between ${\mathrm{AR}}_{\mathrm{AP}}$ and ${\mathrm{AR}}_{P}$ when the layer magnetizations are aligned parallel (P). For Co/Cu/Co, the decrease is larger than expected without mfp effects, but on the borderline of experimental uncertainty. For Co/Ag/Co and Co/Au/Co, the decreases can be explained by effects of best-estimate finite spin-diffusion lengths. Due to uncertainties in these lengths and the data, mfp effects cannot be ruled out. But any mfp effects seem to be small enough that analyses neglecting them should be adequate for evaluating potential sensors.