Crystallographic and magnetic properties of TixCo1+xFe2-2xO4 ferrite powders

The TixCo1+xFe2-2xO4(0.0 less than or equal to x less than or equal to 0.7) ferrite powders are fabricated by a sol-gel method. The growth of particles, crystallographic and magnetic properties of powders are investigated by X-ray diffraction, Mossbauer spectroscopy and vibrating sample magnetometer. TixCo1+xFe2-2xO4 (x = 0.2) ferrite powder annealed at and above 873 K have only a single spinel structure and behave ferrimagnetically. Powder annealed at 773 K has a typical spinel structure and shows a paramagnetic and ferrimagnetic nature, simultaneously. The formation of nano-crystallized particles is confirmed when TixCo1+xFe2-2xO4 (x = 0.2) powder is annealed at 673K. The magnetic behavior of powders annealed at and above 673 K shows that an increase in the annealing temperature yields a decrease in the coercivity and, in contrast, an increase in the saturation magnetization. In the TixCo1+xFe2-2xO4 (x = 0.2) ferrite powder the maximum coercivity and the saturation magnetization are 1564 Oe and 62.6 emu/g, respectively. All the structures of TixCo1-xFe2-2xO4 (0.0 less than or equal to x less than or equal to 0.7) ferrite powders are spinel, and the lattice constants increase with increasing x. The Mossbauer spectra at room temperature, consisted of two Zeeman sextets (0.0 less than or equal to x less than or equal to 0.4) due to Fe3+ ions at tetrahedral and octahedral sites, changed gradually to a doublet (x = 0.7). The variation of Mossbauer parameters with the crystallographic and magnetic properties of powders have been discussed. The magnetic hyperfine fields decrease with increasing x in TixCo1+xFe2-2xO4(0.0 less than or equal to x less than or equal to 0.7). The coercivity decreases fast but the saturation magnetization decreases slowly with increasing x in TixCo1+xFe2-2xO4. (C) 2001 Elsevier Science B.V. All rights reserved.