Interactive effect of impurities on giant magnetoresistance of Co–Fe/Cu multilayers

Giant magnetoresistance of Co–Fe–B/Cu multilayers fabricated in the sputtering atmosphere, where the amount of oxygen impurity is varied, is discussed in connection with their interfacial roughness. The magnetoresistance (MR) ratio of Co–Fe/Cu multilayers is enhanced by up to 33% when the oxygen content is varied between 10 and 100 ppm of processing Ar gas. The enhancement of the MR ratio was due to the flattening effect of impurity oxygen on the multilayer interfaces: the root mean square roughness of the multilayer was decreased from 7.5 to 5 Å. With increasing boron content in Co–Fe layers, however, the enhancing effect of MR ratio by oxygen diminished and nearly vanished for 12 at%-B–(Co–Fe) case. The strong affinity of boron for oxygen is suggested as a probable mechanism.