The effects of the size and structure on magnetic behavior of core/shell nanoparticles

Molecular dynamics (MD) simulations have been employed to simulate the structure of Ni nanoparticles (NPs). These NPs consist of 500, 1372, 2916 and 5324 atoms. Various structures of these NPs, consisting of faced-centered cubic (fcc), hexagonal closed packed (hcp), icosahedral (ico) and amorphous states, have been simulated by changing the cooling rate from 2000 to 300 K. The models of mixed core/shell spin (1, 3/2) have been set based on the NPs. Monte Carlo (MC) simulation has been applied to investigate the magnetic behavior and phase diagrams of the models. We have found that the structure of the models plays important role on the characteristic phase diagrams. The effects of the atomic number as well as the exchange coupling J[Formula: see text]/J[Formula: see text] (J[Formula: see text] — the shell coupling and J[Formula: see text] — the core coupling) on the thermal and magnetic behaviors of the models have been presented and discussed. The phase diagrams in k[Formula: see text]T/J[Formula: see text]−J[Formula: see text]/J[Formula: see text] plane also have been observed by changing the structure and the number atoms of the models.