Room temperature ferromagnetism in Cu2+ doped TiO2 nanocrystals: The impact of their size, shape and dopant concentration

Abstract

Cu2+ doped TiO2 nanocrystals were synthesized using dispersions of titania nanotubes in the presence of Cu2+ ions as a precursors. The morphologies of nanotubular titania precursors and resulted Cu2+ doped TiO2 nanocrystals were characterized by TEM. Structural and optical properties were studied by XRPD analysis and UV-vis spectroscopy in reflectance mode, respectively. Their magnetic properties were investigated using SQUID magnetometer. Tetragonal anatase crystalline structure was confirmed in all synthesized samples. Polygonal (d similar to 15 nm) and spheroid like (length, up to 90 nm) Cu2+ doped TiO2 nanocrystals in samples synthesized at different pHs were observed by TEM. Ferromagnetic ordering with almost closed loop (H-c similar to 200 Oe) was detected in all Cu2+ doped TiO2 nanoparticle films. The saturation magnetization values varied depending on the Cu2+ concentration, nanoparticles shape, size and consequently different number of oxygen vacancies. This study revealed possibility to control magnetic ordering by changing the shape/aspect ratio of Cu2+ doped TiO2 nanocrystals.