Morphology and structure of the interface in Ni/Ge thin films being due to the mutual diffusion of these elements are investigated with the help of atomic force microscope, high resolution electron microscope and micro-diffraction. Strong effect of interface in magnetic behavior of Ni layers is demonstrated and explained by formation of magnetic order in the interface and rough boundaries between layers.

The surface morphology and local structure of layers in the Ni-Ge and Ge-Ni-Ge-Ni-Ge films have been investigated. It has been shown that the surface of the films follows the roughnesses of the substrate surface, which have characteristic dimensions of 2–4 nm in height and ∼100 nm in plane. It has been found that an interface with the depth ranging from 9 to 18 nm is formed at the boundaries between the Ni and Ge layers. The data obtained have been used to explain the specific features of the magnetic properties of the studied films, such as the asymmetry of hysteresis loops at low temperatures and the difference between the temperature dependences of the magnetization of the samples for two cooling modes: in a magnetic field and without a magnetic field.

Magnetic and magneto-optical properties of layered Ge–Ni–Ge–Ni–Ge films have been investigated with the morphology of the film surface being studied also. It is shown that the films reproduce roughness of the glass-substrate surface which is similar to the grains 2–4nm high and 100–400nm long in any direction within the film plane. Thermal treatment results in a decrease of the grains height and their broadening. Non-monotonous change of the Faraday rotation (FR) value due to thermal treatment has been revealed. The inverse linear FR value dependence on the intermediate Ge layer thickness has been obtained. The exchange bias effect is observed at temperatures lower than approximately 50K which was ascribed to the formation of the complex composition interface due to the Ge and Ni mutual diffusion.

Magnetic and magneto-optical properties of the Ni-Ge bilayer films are studied. The unusual temperature behavior of the magnetization curves is revealed: the hysteresis loops at room temperature have a near-rectangular shape; when the films are cooled down to 4.2 K, the coercive force increases by more than an order of magnitude and the asymmetry and displacement of the loop along the field axis are observed. These effects are stronger in thinner Ni layers. The observed features are attributed to the effect of the interlayer between the Ni and Ge layers, which has a complex magnetic structure.