Synthesis and magnetic properties of AlxCoFe2−xO4 ferrite powders

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)