The effect of an inhomogeneous magnetic field on the structure of thin Co films obtained by magnetron sputtering

•C/Co/C coatings were deposited by magnetron sputtering in external magnetic field.•The direction of an external magnetic field influences on cobalt layer structure.•Horizontal magnetic field impedes the process of cobalt grains growth.•Vertical magnetic field promotes strong growth of crystalline cobalt grains. The strong influence of the orientation of an external magnetic field of a system of permanent magnets on the crystal structure of cobalt films grown on an amorphous carbon sublayer was revealed by the methods of transmission electron microscopy and selected area diffraction. While the horizontal component of the magnetic field strength impedes the process of cobalt grains growth, the vertical one, on the contrary, contributes to this process. The vertical component of the magnetic field promotes strong growth of crystalline cobalt grains with an axis [0001] perpendicular to the film surface at the expense of grains with different orientations. As the strength of the vertical component of the magnetic field increases to H ≈ 1.2 × 104 Oe, the size of some crystalline grains with orientation [0001] reaches about 1 μm in the cobalt film with a nominal thickness of 8 nm. In a horizontal magnetic field of the order of 1.2 × 104 Oe, the average grain size is only 16 nm, which is only twice the nominal film thickness. The paper discusses issues related to the influence of magnetic crystallographic anisotropy and external magnetic field on the processes of nucleation during structure rearrangement.