Formation and strain distribution of Ni/NiO core/shell magnetic nanoparticles fabricated by pulsed laser deposition

Abstract

Nucleation and growth lead to substantial strain in nanoparticles embedded in a host matrix. The distribution of strain field plays an important role in the physical properties of nanoparticles. Magnetic Ni/NiO core/shell nanoparticles embedded in the amorphous Al₂O₃ matrix were fabricated by pulsed laser deposition. The results from a high-resolution transmission electron microscope also revealed that the core/shell nanoparticles consist of a single crystal Ni core with a faced-centered cubic structure (Space Group FM-3M) and polycrystalline NiO shell with a trigonal/rhombohedral structure (Space Group R-3mH). The growth strain of Ni/NiO core/shell nanoparticles embedded in the Al₂O₃ matrix was investigated. Finite element calculations clearly indicate that the NiO shell incurs large compressive strain. The compressive strain existing at the NiO shell area enables the shell material at the interface to adapt to the lattice parameters of Ni core. This process results in a relatively good crystallinity near the interface, which may be associated with the higher exchange coupling between the ferromagnetic Ni core and antiferromagnetic NiO shell.