Structure Features of the Nanocrystalline Ni Films Formed by Ion Sputtering Technique

Thinnanocrystalline Ni films with a thickness of similar to 340-360 nm are synthesized by ion sputtering on single crystal Si(111) substrates under high vacuum conditions. X-ray diffraction, scanning electron microscopy with microanalysis, vibration magnetometry and differential thermomagnetic analysis are used to study structure, magnetic phase composition, and magnetic properties of the initial and thermally annealed Ni films. It is found that, under certain deposition modes, the initial nickel films at room temperature have a saturation magnetization by an order of magnitude lower than that of nickel, and after thermal annealing at a temperature of 723 K, they exhibit magnetic anisotropy perpendicular to the surface. It is shown that the reduced value of the saturation magnetization is associated with a significant (3%) tensile deformation of the crystal lattice of nickel. It is found that the perpendicular magnetic anisotropy in the annealed films is due to the presence of tensile macro-stresses because of the differences in the thermal expansion coefficients of the film and the substrate.