No abstract

Nano-sized nickel substituted cobalt ferrite powders, Ni x Co 1-x Fe 2 O 4 (0.0 ≤ x ≤ 1.0), were fabricated by the sol-gel method, and their crystallographic and magnetic properties were studied. All the ferrite powders showed a single spinel structure, and behaved ferrimagnetically. When the nickel substitution was increased, the lattice constants and the sizes of particles of the ferrite powders decreased. The Mössbauer absorption spectra of Ni x Co 1-x Fe 2 O 4 ferrite powders could be fitted with two six-line subspectra, which were assigned to a tetrahedral A-site and octahedral B-sites of a typical spinel crystal structure. The increase in values of the magnetic hyperfine fields indicated that the superexchange interaction was stronger, with the increased nickel concentration in Ni x Co 1-x Fe 2 O 4 . This could be explained using the cation distribution, which can be written as,The two values of the saturation magnetization and the coercivity decreased, as the rate of nickel substitution was increased. These decreases could be explained using the cation distribution, the magnetic moment, and the magneto crystalline anisotropy constant of the substituted ions.

Nickel substituted manganese ferrites, Mn 1-x Ni x Fe 2 O 4 (0.0 ≤ x ≤ 0.6), were fabricated by sol-gel method. The effects of sintering and substitution on their crystallographic and magnetic properties were studied. X-ray diffractometry of Mn 0.6 Ni 0.4 Fe 2 O 4 ferrite sintered above 523 K indicated a spinel structure; particles increased in size with hotter sintering. The Mössbauer spectrum of this ferrite sintered at 523 K could be fitted as a single quadrupole doublet, indicative of a superparamagnetic phase. Sintering at 573 K led to spectrum fitted as the superposition of two Zeeman sextets and a single quadrupole doublet, indicating both ferrimagnetic and paramagnetic phase. Sintering at 673 K and at 773 K led to spectra fitted as two Zeeman sextets due to a ferrimagnetic phase. The saturation magnetization and the coercivity of Mn 0.6 Ni 0.4 Fe 2 O 4 ferrite sintered at 773 K were 53.05 emu/g and 142.08 Oe. In Mn 1-x Ni x Fe 2 O 4 (0.0 ≤ x ≤ 0.6) ferrites, sintering of any composition at 773 K led to a single spinel structure. Increased Ni substitution decreased the ferrites' lattice constants and increased their particle sizes. The Mössbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and the octahedral sites of the Fe 3+ ions. The variations of saturation magnetization and coercivity with changing Ni content could be explained using the changes of particle size.