Superferromagnetism in chain-like Fe@SiO₂ nanoparticle ensembles

One-dimensional (1D) chain-like nanocomposites, created by ensembles of nanoparticles of with diameter ∼ 13 nm, which are composed of an iron core (∼4 nm) and a silica protective layer, were prepared by a self-assembly process. Chain-like Fe@SiO₂ ensembles were formed due to strong magnetic dipole–dipole interactions between individual Fe nanoparticles and the subsequent fixation of the Fe particles by the SiO₂ layers. X-ray near edge absorption spectra measurements at the Fe K absorption edge confirm that the presence of a silica layer prevents the oxidation of the magnetic Fe core. Strong magnetic interactions between Fe cores lead to long-range ordering of magnetic moments, and the nanoparticle ensembles exhibit superferromagnetic characteristics demonstrated by a broad blocking Zero-field cooling (ZFC)/field-cooling distribution, nearly constant temperature dependence of ZFC magnetization, and non-zero coercivity at room temperature. Low room-temperature coercivity and the presence of electrically insulating SiO₂ shells surrounding the Fe core make the studied samples suitable candidates for microelectronic applications.