Ferromagnetism in Cr-, Fe-, and Ni-doped TiO₂ samples

Highlights: • Cr-, Fe-, and Ni-doped TiO₂ (0.2%) nanopowders were prepared by a solid-state method. • PL studies revealed the presence of oxygen defect related emission peaks in all the samples. • The Ms values for the Cr-, Fe-, and Ni-doped TiO₂ are 3.2, 4.6, and 2.9 µ_B, respectively. • The Hc values for the Cr-, Fe-, and Ni-doped TiO₂ are 385, 209, and 382 Oe, respectively. • The high FM was interpreted by the F-center model, in which both V_O and TM ions are involved. - Abstract: Ferromagnetic Cr-, Fe-, and Ni-doped TiO₂ nanopowder samples (with 0.2% Cr, Fe, or Ni) were synthesized using the solid-state reaction method. The X-ray diffraction pattern showed that all the samples possessed typical anatase structure, and no other impurity phases were observed. Ultraviolet–visible spectroscopy (UV–vis) measurements revealed that the band gap decreased due to the incorporation of Cr, Fe, or Ni. The photoluminescence results showed the presence of oxygen defect related emission peaks in Cr-, Fe-, and Ni-doped TiO₂. Room temperature ferromagnetism is observed in all the Cr-, Fe-, and Ni-doped TiO₂ samples. Saturation magnetic moment is the highest for Fe-doped TiO₂. The Fe:TiO₂ samples were found to have a magnetic moment of 4.58 µ_B/Fe, and they seem to have greater ferromagnetism than the Cr/Ni-doped TiO₂ samples. The structural and magnetic investigations demonstrate that ferromagnetism at room temperature is an intrinsic property of the samples. Thus, ferromagnetism does not originate from clusters or secondary phases; it is due to the Cr/Fe/Ni:TiO₂ matrices. This study has shown that substituting a very light percentage of Cr, Fe, or Ni for Ti in TiO₂ gives rise to appreciable room temperature ferromagnetic ordering useful for spintronic applications.