Role of carbon in the formation of the structure and magnetic properties of Ni-CN$_x$ nanoclusters under reactive magnetron deposition

Nanostructured hybrid Ni-CN$_x$ films were grown by magnetron sputtering of a composite graphite-nickel target. Atomic force microscopy showed the clustered nature of the films deposition on the substrate surface: a relatively high pressure in the low-temperature magnetron plasma made it possible to form the Ni@CN$_x$ nanoclusters type “core-shell”, where metallic nickel is the core and carbon nitride is the shell. When studying the role of carbon in the formation of the structure and properties of Ni@CN$_x$ nanoclusters, it was established that the saturation magnetization 4$\pi$M$_s$ of nanoclusters drops sharply with a carbon content above 30 at.%. The reason is the formation of an increasingly saturated solid solution of carbon in nickel. At a carbon concentrations above 38 at.%, amorphous Ni-CN$_x$ nanoclusters are formed in the magnetron plasma, which are deposited on the substrate. An increase in the substrate temperature leads to the crystallization of Ni atoms, and the C and N atoms are forced out onto the surface of the nickel core, forming an array of Ni-CN$_x$ elements.