Abstract
Co doped TiO2 nanopowder has been synthesized by a simple sol–gel route. XRD and TEM analysis confirms anatase phase of TiO2 with crystallite and particle sizes of 10 and 15 nm respectively. Presence of Co is confirmed by EDX. FTIR shows a slight shift in the Ti-O bonding vibration to lower frequency suggesting dopant incorporation on Ti site. For magnetic measurements the sample with dopant amount x = 0.075 is annealed both in vacuum and air. Weak ferromagnetism and a blocking temperature of 39 K is obtained for vacuum annealed sample while ferromagnetism is lost in the air annealed sample and shows only paramagnetic behavior. Temperature dependent magnetic measurements for air annealed sample shows antiferromagnetic behavior with a Neel temperature of 36.51 K. Here we report that oxygen vacancy and cobalt aggregates is a key factor for inducing ferromagnetism–superparamagnetism in vacuum annealed sample. Appearance of Neel temperature reveals the presence of antiferromagnetic Co3O4 which is the oxidation results of metallic Co or cobalt clusters present on host TiO2 surface.
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