Room-temperature ferromagnetism in Ni2+ doped TiO2 nanocrystals synthesized from nanotubular precursors

Highlights: • Ni2+ doped TiO2 nanocrystals from titania nanotubes. • RT ferromagnetism (Hc ∼ 150–200 Oe) in Ni2+ doped TiO2 nanocrystals. • Crystal structure of TiO2 matrix is independent on dopant concentration. • The magnetic properties are influenced by the nickel concentrations in different ways. -- Abstract: Hydrothermal synthetic route for synthesis of Ni2+ doped TiO2 nanocrystals showing room temperature ferromagnetism, using dispersion of titania nanotubes in the presence of Ni2+ ions at different pHs as precursors, is reported. Morphologies of tubular precursors and Ni2+ doped TiO2 nanocrystals were characterized by transmission electron microscopy. Titania nanotubes have outer diameter of about 10 nm while the length varies widely even reaching few hundred nanometers. Ni2+ doped TiO2 nanoparticles synthesized at pH 3 have polygonal shape and dimension of about 20 nm. Transmission electron microscopy analysis revealed presence of mixed shapes (polygonal and rod like) in the sample of Ni2+ doped TiO2 nanoparticles synthesized at pH 5. X-ray diffraction analysis of resultant powder and selected area electron diffraction pattern confirmed the anatase crystal phase of Ni2+ doped TiO2 nanoparticles independently of dopant concentrations (0.09, 0.25, 0.86, 1.48 and 1.80 at%), followed by slight changes of their microstructural parameters. Reflection spectra of Ni2+ doped TiO2 nanoparticles revealed their altered optical properties in comparison to undoped TiO2 nanoparticles. Room temperature ferromagnetic ordering with saturation magnetic moment in the range of 10−3–5 × 10−2 μB per Ni atom was observed for all measured films made of Ni2+ doped TiO2 nanoparticles