Structural and phase transformation of cobalt films grown on amorphous carbon

Publication date: 31 January 2017
Source:Thin Solid Films, Volume 622
Author(s): E.N. Zubarev, A.Yu. Devizenko, O.V. Penkov, V.V. Kondratenko, D.V. Sevriukov, V.A. Sevryukova, I.A. Kopylets
Structural evolution of the ultra-thin cobalt layers grown on amorphous carbon by DC magnetron sputtering were studied in detail by transmission electron microscopy and low-angle X-ray diffraction for a range of the cobalt thickness from 1.5nm to 4.6nm. It was shown that atomic structure of cobalt layers was amorphous at the layer thicknesses below 2nm, an amorphous matrix with embedded nuclei of the crystalline phase with in-plane size of 1–2nm in the thickness range from 3nm to 3.2nm, and polycrystalline with the randomly oriented HCP cobalt grains at thicknesses over 4nm. Increase of the cobalt thickness from 3.2nm to 4.6nm led to growth of the cobalt grains with in-plane average size up to ~70nm by the normal grain coarsening process. Transition of the atomic structure of cobalt from the isotropic amorphous state to the anisotropic crystalline state in the thickness range of ~2–4nm was accompanied by deterioration of the magnetization vector direction within the ferromagnetic domains due to high magnetic anisotropy of HCP lattice of cobalt.