Influence of NicoreAushell Nanoparticles’ Morphology on Their Magnetic Properties

This paper reveals and describes the features of NicoreAushell 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) × 104 J/m3) 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 near-surface “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 NicoreAushell nanoparticles. This long-term study was completed by the present investigation as the most detailed for magnetic-diamagnetic core–shell systems nanosized nowadays.