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

Keywords: Cobalt ferrite Gd-substitution Raman spectroscopy Magnetic properties Neel temperature a b s t r a c t Polycrystalline gadolinium (Gd) substituted cobalt ferrites (CoFe 2Àx Gd x O 4 ; 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 (GdFeO 3) 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 P 0.3). No contribution from ortho-ferrite GdFeO 3 phase is noted to the magnetic properties. The increase in the magnetic saturation magnetization is attributed to the higher magnetic moment of Gd 3+ (4f 7) residing in octahedral sites is higher when compared to that of Fe 3+ (3d 5) and as well due to the migration of Co 2+ (3d 7) ions from the octahedral to the tetrahedral sites with a magnetic moment aligned anti-parallel to those of rare earth (RE 3+) ions in the spinel lattice. Increase in coercivity with increase in Gd 3+ is content is attributed to magnetic anisotropy in the ceramics. Ferrimagnetic materials, are an important class of magnetic ceramics, have drawn much attention for the past few decades due to their remarkable properties like high saturation magnetiza-tion, large permeability at high frequency, low eddy current, and high electrical resistivity to be utilized in solid state electronics and magneto-electronics [1–15]. Particularly, rare earth (RE) ion substituted spinel ferrites are reported to be promising candidates for applications in high-density storage (magnetic cores of read write heads for high-speed digital tape or disk recording), magnetic sensors, magnetic fluids, telecommunication equipments, magnetically guided drug or radioactive nuclide delivery, remote detoxification, radio frequency coils, transformer cores, rod antennas, and are also good candidates for microwave applications [2,3]. In AB 2 O 4 type centrosymmetric spinel ferrites, the metal ions are situated in two different sub-lattices designated tetrahedral (A-site) and octahedral (B-site) in a unit cell. Magnetic and electrical properties of these ferrites depend on the nature and distribution of their cations in the two tetrahedral and octahedral sub-lattices of a cubic structure [4,5]. These high Curie temperature magnetic insulators …