Current-in-plane transport in granular single layers and multilayers of CoFe in Al2O3

The dependence of current-in-plane resistance (R) and magnetoresistance (MR) of Al2O3(30 A)/[Co80Fe20(13 A)/Al2O3(30 A)]n granular layered films on the number of bilayers n was studied. It was found experimentally that R is proportional to 1/n, whereas MR is practically independent of n. According to simple model calculations, significant deviations from R∝1/n should be expected for thick interlayer Al2O3 spacers sperpendicular, combined with thin intergrain bridges within the layers, sparallel<sperpendicular. The discrepancy between the model and the experiment is attributed to the effects of inhomogeneities in sparallel and sperpendicular and to the presence in each layer of a small amount of large metallic patches, which can effectively shortcut the neighboring layers. For buffer Al2O3 layer thickness above 50 A both R and MR decrease drastically, which is explained by the appearance of more patches at smoother Al2O3 surface. In contrast to the granular layered structures based on SiO2 and HfO2, the annealing in our system lowers MR values, presumably due to the oxidation of CoFe granules already existing in the as-deposited layers