Synthesis and magnetic properties of AlxCoFe2?xO4 ferrite powders

Abstract

AlxCoFe2−xO4(0.00 ≤ x ≤ 0.20) ferrite powders were fabricated by the sol–gel method. The growth of particles and the crystallographic and magnetic properties of powders were investigated using X-ray diffraction, field emission electro microscopy, Mössbauer spectroscopy, and a vibrating sample magnetometer. AlxCoFe2−xO4 (x = 0.20) ferrite powder annealed at 773 K has only a single spinel structure and behaves ferrimagnetically. Powder annealed at 673 K has a coexistence of paramagnetic and ferrimagnetic phases. Study on the magnetic behavior of powders show that an increase in the annealing temperature yields a decrease in coercivity and an increase in saturation magnetization. In the AlxCoFe2−xO4 (x = 0.20) ferrite powder, the maximum coercivity is 950 Oe. All the structures of AlxCoFe2−xO4 (0.00 ≤ x ≤ 0.20) ferrite powders annealed at 1073 K are spinel, and the lattice constants decrease with increasing x. The room temperature Mössbauer spectra consisted with two Zeeman sextets due to Fe3+ ions at tetrahedral and octahedral sites. The variation of Mössbauer parameters has been discussed in terms of the crystallographic and magnetic properties of powders. The magnetic hyperfine fields decrease when x is increased in AlxCoFe2−xO4 (0.00 ≤ x ≤ 0.20). Likewise, coercivity and saturation magnetization also decrease when x is increased in AlxCoFe2−xO4 (0.00 ≤ x ≤ 0.20). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)