Ferromagnetism and Superparamagnetism in Co-doped TiO2 Nanoparticles

Strategic Insights -

Ferromagnetism and superparamagnetism have been observed in Co-doped TiO2 nanoparticles, which is attributed to the presence of oxygen vacancies and cobalt aggregates. The doped nanoparticles were synthesized using a sol-gel route with varying cobalt concentrations. The researchers found that the increase in d-spacing and valence states of Co confirmed the presence of the dopant material. The vacuum-annealed samples showed weak ferromagnetism, while the air-annealed sample exhibited only paramagnetic behavior. The temperature-dependent magnetic measurements revealed antiferromagnetic behavior in the air-annealed sample.

Key Takeaways:

  • Co-doped TiO2 nanoparticles were synthesized with cobalt concentrations of 7.5, 9.5, and 10.5 mol%.
  • The increase in d-spacing for the (0 0 4) and (2 0 0) peaks confirmed the presence of impurity content.
  • XPS and EDX analysis revealed the valence states of Co and its presence in the doped material.
  • Weak ferromagnetism was observed in vacuum-annealed samples, while air-annealed samples displayed paramagnetic behavior.
  • A blocking temperature of 37.9 K was obtained, which shifted to higher temperatures with increased dopant concentration.
  • Temperature-dependent magnetic measurements revealed antiferromagnetic behavior in air-annealed samples with a Curie-Weiss temperature of -16 K.
  • Oxygen vacancy and cobalt aggregates were identified as key factors in inducing ferromagnetism-superparamagnetism in vacuum-annealed samples.
  • The appearance of negative Curie-Weiss temperature indicated the presence of antiferromagnetic Co3O4, resulting from the oxidation of metallic Co or cobalt clusters.
  • Tezpur University researchers concluded that the presence of oxygen vacancies and cobalt aggregates affects the magnetic properties of Co-doped TiO2 nanoparticles.

Statistics:

  • 7.5, 9.5, and 10.5 mol% cobalt concentrations were used in the synthesis of Co-doped TiO2 nanoparticles.
  • A 37.9 K blocking temperature was obtained, which shifted to higher temperatures with increased dopant concentration.
  • -16 K Curie-Weiss temperature was observed in air-annealed samples indicating antiferromagnetic behavior.

Sources:

  • B. Choudhury, et al. (2011). Effect of oxygen vacancy and dopant concentration on the magnetic properties of high spin Co2+ doped TiO2 nanoparticles. Journal of Magnetism and Magnetic Materials, 323(5), 440-446.
  • A. Choudhury, Tezpur University, Dept. of Physics, Tezpur 784028, Assam, India.
  • Elsevier Science BV, PO Box 211, 1000 AE Amsterdam, Netherlands.