Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, MnFe 2 O 4 , Mn 0.8 Co 0.2 Fe 2 O 4 , Mn 0.8 Zn 0.2 Fe 2 O 4 and Mn 0.8 Ni 0.1 Zn 0.1 Fe 2 O 4 , were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The MnFe 2 O 4 ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The Mössbauer spectrum of the MnFe 2 O 4 ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the Mössbauer spectra of the MnFe 2 O 4 , Mn 0.8 Co 0.2 Fe 2 O 4 , and Mn 0.8 Zn 0.2 Fe 2 O 4 ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe 3+ ions. However, the Mössbauer spectrum of the Mn 0.8 Ni 0.1 Zn 0.1 Fe 2 O 4 ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the Mössbauer spectra could be used to determine the cation distribution equation, and we also explained the variation in the Mössbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure MnFe 2 O 4 , the saturation magnetizations and coercivities were larger in Mn 0.8 Co 0.2 Fe 2 O 4 and smaller in Mn 0.8 Zn 0.2 Fe 2 O 4 , and Mn 0.8 Ni 0.1 Zn 0.1 Fe 2 O 4 . These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.

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The crystallographic and magnetic properties of gallium-substituted cobalt ferrite (CoGa x Fe 2-x O 4 ) were investigated. The new material was synthesized using conventional ceramic methods, with gallium substituted for ferrite in the range of x = 0.0 to 1.0, in steps of 0.2. X-ray diffraction and Mössbauer spectroscopy were used to confirm the presence of crystallized particles in the CoGa x Fe 2-x O 4 ferrite powders. All of the samples exhibited a single phase with a spinel structure, and the lattice parameters decreased as the gallium content increased. The particle size of the samples also decreased as gallium increased. For x ≤ 0.4, the Mössbauer spectra of CoGa x Fe 2-x O 4 could be fitted with two Zeeman sextets, which are the typical spinel ferrite spectra of Fe 3+ with A-and B-sites. However, for x ≥ 0.6, the Mössbauer spectra could be fitted with two Zeeman sextets and one doublet. The variation in the Mössbauer parameters and the absorption area ratio indicated a cation distribution of (Co 0.2-0.2x Ga x Fe 0.8-0.6x )[Co 0.8+0.2x Fe 1.2-0.4x ]O 4 , and the magnetic behavior of the samples suggested that the increase in gallium content led to a decrease in the saturation magnetization and in the coercivity.

The effects of manganese substitution on the crystallographic and magnetic properties of Li-Zn-Cu ferrite, Li 0.5 Zn 0.2 Cu 0.4 Mn x Fe 2.1-x O 4 (0.0 ≤ x ≤ 0.8), were investigated. Ferrites were synthesized via a conventional ceramic method. We confirmed the formation of crystallized particles using X-ray diffraction, field emission scanning electron microscopy and Mössbauer spectroscopy. All of the samples showed a single phase with a spinel structure, and the lattice constants linearly decreased as the substituted manganese content increased, and the particle size of the samples also somewhat decreased as the doped manganese content increased. All the Mössbauer spectra can be fitted with two Zeeman sextets, which are the typical spinel ferrite spectra of Fe 3+ with A-and B-sites, and one doublet. The cation distribution was determined from the variation of the Mössbauer parameters and of the absorption area ratio. The magnetic behavior of the samples showed that an increase in manganese content led to a decrease in the saturation magnetization, whereas the coercivity was nearly constant throughout. The maximum saturation magnetization was 73.35 emu/g at x = 0.0 in Li 0.5 Zn 0.2 Cu 0.4 Mn x Fe 2.1-x O 4 .