Role of carbon in the formation of the structure and magnetic properties of Ni@CNx nanoclusters under reactive magnetron deposition

Abstract

Nanostructured hybrid Ni-CNx 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@CNx 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@CNx nanoclusters, it was established that the saturation magnetization 4πMs 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-CNx 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@CNx elements.

Structure, Thermal Stability, and Magnetism of Ni4N Thin Films

“…Whereas, experimentally, Ni 4 N thin films have been found to be FM at 300 K with . [ 30,31 ] These experimental observations are in contradiction with the theoretical predictions. Here, it is worth mentioning that those Ni 4 N films were either deposited at a high (about 625 K) or some impurity of Ni phase was present.…”

“…Here, it is worth mentioning that those Ni 4 N films were either deposited at a high (about 625 K) or some impurity of Ni phase was present. [ 30–32 ] In addition, the crystal structure of Ni 4 N seems to be unclear hitherto. Two different possible structures for Ni 4 N have been observed namely Ni 4 N‐I and Ni 4 N‐II.…”

“…The magnetization of Ni 4 N is debated to be PM or FM at 300 K. [ 30,31 ] Though, theoretical calculation clearly predicts the PM state of Ni 4 N at 300 K and a FM state below its Curie temperature ( T c ) of about 121 K. [ 4 ] Therefore, the appearance of a FM state at 300 K is dubious in Ni 4 N. [ 30,31 ] From our N self‐diffusion measurements, it becomes clear that N starts to diffuse out from Ni–N, when growth or annealing temperature exceeds 450 K. Therefore, FM Ni 4 N may be due to the presence of FM Ni. This further becomes clear by comparing the polarized neutron reectivity (PNR) pattern (taken at 300 K) of samples grown at and 475 K. As shown in Figure , the observable splitting between spin up () and down () reflectivities in sample confirms its FM nature; [ 54 ] however, the absence of such splitting in the sample signifies its PM state.…”

Some features of the thermoelectric properties of the "metal-carbon film" junction

“…As shown in [7], the temperature dependence of film resistance has classical semiconductor character -the resistance decreases with the temperature increasing. Thus, it is obvious that as a result of the work, the "metal-semiconductor" contact junction was obtained (where the semiconductor is the carbon film), which is the subject of this study.…”

“…Carbon films were deposited on substrates made of dielectric (cover glass) and various metals (titanium, steel, niobium, etc.) [7]. Plasma was created using a planar DC magnetron with a flat cathode and an annular anode.…”