Evidence for a self-organized growth in granular Co/Al2O3 multilayers

Abstract

By sequential deposition of thin layers of cobalt and alumina by sputtering, we have fabricated granular multilayers consisting of successive planes of nanosized cobalt clusters separated by alumina along the growth direction. Combining grazing-incidence small-angle x-ray scattering and transmission electron microscopy experiments, we show that, in a given range of thickness, the vertical arrangement of clusters from plane to plane is not random but shows a topology-induced self-organization.

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

“…We give in Table I a list of the important parameters obtained from these experiments for all samples studied. Finally, the TEM pictures reveal a quasi-ordered arrangement of the Co clusters 16 that is induced by the topology of the layers: the clusters of a layer nucleate preferentially in the hollows left by the previous layer. In each layer, the average distance between the borders of adjacent clusters is of order 2 nm and approximately independent of t Co .…”

“…A given sample is usually made by piling up a number N (1 to 100 for the samples studied here) of these layers. 16 The deposition rates of both Co and alumina were respectively 0.114Å s −1 and 0.43Å s −1 . It was found that the amount of Co deposited on the surface is larger than the Co mass which forms clusters visible by transmission electron microscopy (TEM).…”

“…[14][15][16] The Co aggregates were prepared by sputter deposition of Co atoms on a smooth alumina surface. The amount of deposited Co is given here by the nominal thickness t Co that the deposits would have if they were homogeneous.…”

“…It was also found that, for a range of thicknesses, a relatively ordered disposition of the particles is obtained, in which they are arranged in layers separated from the adjacent ones by a controllable distance. 16 The paper is organized as follows. In the first two sections we briefly describe the method employed to prepare the samples and their physical characterization.…”

“…We present the magnetic characterization of a new type of systems of Co nanoparticles, embedded in an amorphous matrix of Al 2 O 3 , prepared by sequential deposition of both materials. [14][15][16] By varying the deposition time, the diameter of the aggregates can be controlled between below 1 nm and 7 nm. An important advantage of this preparation method is that it gives a rather homogeneous dispersion of the particles in the matrix.…”