Defect-mediated high-temperature ferromagnetism in oxide nanocrystallites was studied. The development of room-temperature ferromagnetism in nanosized Co-doped barium titanate particles with a size of about 14nm, and synthesized using a solvothermal drying method, was studied. A combination of X-ray diffraction with state-of-the-art electron microscopy techniques confirmed the intrinsic doping of Co into BaTiO3. The development of the room-temperature ferromagnetism was traced to the various donor defects: hydroxyl groups at the oxygen site (OH•(O)) and oxygen vacancies (V••(O)), and their relative concentrations at the surface and the core of the nanocrystal. These could be controlled by post-synthesis drying and thermal treatments.

Defect Controlled Room Temperature Ferromagnetism in Co-Doped Barium Titanate Nanocrystals. S.Ray, Y.V.Kolenko, K.A.Kovnir, O.I.Lebedev, S.Turner, T.Chakraborty, R.Erni, T.Watanabe, G.Van Tendeloo, M.Yoshimura, M.Itoh: Nanotechnology, 2012, 23[2], 025702