Structure features of the nanocrystalline Ni films formed by ion sputtering technique

Thin nanocrystalline Ni films with a thickness of $\sim$ 340–360 nm were synthesized by ion sputtering on single-crystal Si (111) substrates under high vacuum conditions. The structure, magnetic phase composition, and magnetic properties of the as-deposited and thermally annealed Ni films were studied by X-ray diffraction, scanning electron microscopy with microanalysis, vibration magnetometry, and differential thermomagnetic analysis. It was found that, under certain deposition regimes, the as-deposited 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 strain of the crystal lattice of the nickel. It was found that the perpendicular magnetic anisotropy of the annealed films is due to the presence of tensile macrostresses due to differences in the thermal expansion coefficients of the film and substrate.