Stabilization of superparamagnetic nickel nanoparticles in a sepiolite matrix

Superparamagnetic nickel-rich nanoparticles at room temperature have been obtained in a silicate matrix (sepiolite) by a chemical route. During the synthesis process, the control of the acid treatment of the matrix allows nickel cations being incorporated in different locations, into the octahedral site of the structural channels or being deposited onto the sepiolite surface. Thus, two different types of nickel nanoparticles have been obtained depending on the nature of the acid attack: small (similar to 7 nm) and embedded superparamagnetic, or large (similar to 27 nm) deposited single domain nickel nanoparticles for strong or weak acid attack, respectively. Moreover, the embedded nanoparticles have been revealed to possess a remarkable stability against complete oxidation. According to the usage of characterization techniques (transmission electron microscopy, X-ray diffraction and magnetic measurements), embedded nanoparticles seem to be coated with a non-ferromagnetic coating that hinders the oxygen diffusion.