Effect of oxygen vacancy and dopant concentration on the magnetic properties of high spin Co doped TiO2 nanoparticles |
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Authors: | B. ChoudhuryA. Choudhury A.K.M. Maidul IslamP. Alagarsamy M. Mukherjee |
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Affiliation: | a Department of Physics, Tezpur University, Tezpur 784028, Assam, India b Surface Physics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India c Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India |
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Abstract: | Co doped TiO2 nanoparticles have been synthesized by a simple sol-gel route taking 7.5, 9.5 and 10.5 mol% of cobalt concentration. Formation of nanoparticles is confirmed by XRD and TEM. Increase in d-spacing occurs for (0 0 4) and (2 0 0) peak with increase in impurity content. Valence states of Co and its presence in the doped material is confirmed by XPS and EDX. The entire vacuum annealed samples show weak ferromagnetism. Increased magnetization is found for 9.5 mol% but this value again decreases for 10.5 mol% due to antiferromagnetic interactions. A blocking temperature of 37.9 K is obtained, which shows shifting to high temperature as the dopant concentration is increased. The air annealed sample shows only paramagnetic behavior. Temperature dependent magnetic measurements for the air annealed sample shows antiferromagnetic behavior with a Curie-Weiss temperature of −16 K. Here we report that oxygen vacancy and cobalt aggregates are a key factor for inducing ferromagnetism-superparamagnetism in the vacuum annealed sample. Appearance of negative Curie-Weiss temperature reveals the presence of antiferromagnetic Co3O4, which is the oxidation result of metallic Co or cobalt clusters present on the host TiO2. |
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Keywords: | Oxygen vacancy Ferromagnetism Paramagnetism Blocking moment Curie temperature |
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