Chemical bonding and magnetic properties of gadolinium (Gd) substituted cobalt ferrite

Polycrystalline gadolinium (Gd) substituted cobalt ferrites (CoFe2-xGdxO4; x = 0-0.3, referred to CFGO) ceramics have been synthesized by solid state reaction method. Chemical bonding, crystal structure and magnetic properties of CFGO compounds have been evaluated as a function of Gd-content. X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure. However, a secondary ortho-ferrite phase (GdFeO3) nucleates for higher values of Gd-content. A considerable increase in the saturation magnetization has been observed upon the initial substitution of Gd (x = 0.1). The saturation magnetization drastically decreases at higher Gd content (x >= 0.3). No contribution from ortho-ferrite GdFeO3 phase is noted to the magnetic properties. The increase in the magnetic saturation magnetization is attributed to the higher magnetic moment of Gd3+ (4f(7)) residing in octahedral sites is higher when compared to that of Fe3+ (3d(5)) and as well due to the migration of Co2+ (3d(7)) ions from the octahedral to the tetrahedral sites with a magnetic moment aligned anti-parallel to those of rare earth (RE3+) ions in the spinel lattice. Increase in coercivity with increase in Gd3+ is content is attributed to magnetic anisotropy in the ceramics. (C) 2015 Elsevier B.V. All rights reserved.