Influence of Ni_coreAu_shell Nanoparticles’ Morphology on Their Magnetic Properties

Abstract

This paper reveals and describes the features of Ni core Au shell nanoparticles' magnetic properties. Their activation energy of monodomain thermal relaxation (5.1 × 10 −20 J) and constant of magnetic crystalline anisotropy ((2.0−2.1) × 10 4 J/m 3 ) are higher than bulk nickel has. Compared with nanostructured fcc-Ni powders, there is a decrease in the coercive force, the presence of "hard" magnetization, rising magnetization along with increasing degree of the nanoparticles' oxidation, and a decrease in magnetic characteristics to very low values at 300 K. These features are related to the structure of Ni cores (size and ico-structure of their units), shielding by Au shells, Au−Ni solid solution, and Ni(OH) 2 , and their nearsurface "frozen" spin subsystem. The latter depends on the sizes of nanocores and the Au−Ni interface. All of these features were discussed on the basis of material science research the authors provided for the Ni core Au shell nanoparticles. This long-term study was completed by the present investigation as the most detailed for magneticdiamagnetic core−shell systems nanosized nowadays.

Production of nickel and cobalt metal powders under autoclave conditions

“…В статье [12] показана возможность выделения металлических фаз никеля и кобальта из горячих растворов их солей при помощи гипофосфита натрия. Несколько исследований было посвящено изучению процессов восстановления солей Ni(II) и Сo(II) из водных растворов тетрагидридоборатом натрия [13][14][15]. Однако в этих случаях необходимо принимать во внимание возможность загрязнения металлических порошков продуктами разложения гипофосфита и тетрагидридобората натрия соответственно, что в ряде практических приложений, например в гетерогенном катализе, совершенно недопустимо.…”