Fine structure and possible growth mechanisms of some electrodeposited CuCo granular films

Abstract

Granular thin-films of the alloy Cu100−xCox within the composition range 6<x<35 have been grown by electrodeposition. The films have been investigated both magnetically and structurally and a comparison made between both types of measurements. Low field susceptibility measurements have been made which, in principle, allow us to determine the distribution of blocking temperatures and thus make an estimate of particle sizes. Before structural examination, the films were thinned either electrochemically or by ion-etching; both standard electron diffraction and TEM techniques have been employed. We believe that we are able to see Co-rich regions in the vicinity of sub-grain boundaries and that it is these regions that account for the magnetic behaviour of the samples. Whereas electron diffraction patterns from thin sections correspond to the FCC phase only, in thicker sections, additional reflections corresponding to interplanar spacings that cannot be indexed in terms of an FCC phase are observed. The possible origins of these extra reflections are discussed in terms of either double-diffraction at microtwins or, alternatively, in terms of extended, Co-rich HCP phases formed at matrix/twin interfaces. A possible mechanism for the growth of the HCP phase, which is a consequence of the electrodeposition technique, is discussed.