Woo Hyun Kwon

Synthesis and Magnetic Properties of Zn, Co and Ni Substituted Manganese Ferrite Powders by Sol-gel Method

The Zn, Co and Ni substituted manganese ferrite powders, Mn1-x(Zn, Co, Ni) x Fe₂O₄, were fabricated by the solgel method, and their crystallographic and magnetic properties were studied. The Zn substituted manganese ferrite, Zn 0.2 Mn 0.8 Fe₂O₄, had a single spinel structure above 400 ℃, and the size of the particles of the ferrite powder increased when the annealing temperature was increased. Above 500 ℃, all the Mn 1-x (Zn, Co, Ni) x Fe₂O₄ ferrite had a single spinel structure and the lattice constants decreased with an increasing substitution of Zn, Co, and Ni in Mn 1-x (Zn, Co, Ni) x Fe₂O₄. The Mossbauer spectra of Mn 1-x Zn x Fe₂O₄ (0.0≤x≤0.4) could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe 3+ ions. For x = 0.6 and 0.8 they showed two Zeeman sextets and a single quadrupole doublet, which indicated they were ferrimagnetic and paramagnetic. And for x = 1.0 spectrum showed a doublet due to a paramagnetic phase. For the Co and Ni substituted manganese ferrite powders, all the Mossbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe 3+ ions. The variation of the Mossbauer parameters are also discussed with substituted Zn, Co and Ni ions. The increment of the saturation magnetization up to x = 0.6 in Mn 1-x Co x Fe₂O₄ could be qualitatively explained using the site distribution and the spin magnetic moment of substituted ions. The saturation magnetization and coercivity of the Mn 1-x (Zn, Co, Ni) x Fe₂O₄ (x = 0.4) ferrite powders were also compared with pure MnFe₂O₄.

Crystallographic and Magnetic Properties of Co, Zn, Ni-Zn Substituted Nano-size Manganese Ferrites Synthesized by Sol-gel Method

Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, MnFe₂O₄, Mn 0.8 Co 0.2 Fe₂O₄, Mn 0.8 Zn 0.2 Fe₂O₄ and Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The MnFe₂O₄ 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 Mossbauer spectrum of the MnFe₂O₄ ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the Mossbauer spectra of the MnFe₂O₄, Mn 0.8 Co 0.2 Fe₂O₄, and Mn 0.8 Zn 0.2 Fe₂O₄ 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 Mossbauer spectrum of the Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄ 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 Mossbauer spectra could be used to determine the cation distribution equation, and we also explained the variation in the Mossbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure MnFe₂O₄, the saturation magnetizations and coercivities were larger in Mn 0.8 Co 0.2 Fe₂O₄ and smaller in Mn 0.8 Zn 0.2 Fe₂O₄, and Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.

Nickel Substitution Effects on Nano-sized Co, Mn and MnZn Ferrites Synthesized by Sol-gel Method

Nickel substituted nano-sized ferrite powders, Co 1-x Ni x Fe₂O₄, Mn 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ (0.0 ≤ x ≤ 0.2), were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently compared. The lattice constants decreased as quantity of nickel substitution increased, while the particle size decreased in Co 1-x Ni x Fe₂O₄ ferrite but increased for the Mn 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ ferrites. For the Co 1-x Ni x Fe₂O₄ and Mn 1-x Ni x Fe₂O₄ (0.0 ≤ x ≤ 0.2) ferrite powders, the Mossbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe 3+ ions. However, the Mossbauer spectrum of Mn 0.8 Zn 0.1 Ni 0.1 Fe₂O₄ consisted of two Zeeman sextets and one single quadrupole doublet due to the ferrimagnetic and paramagnetic behavior. The area ratio of the Mossbauer spectra could be used to determine the cation distribution equation, and we also explain the variation in the Mossbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. The saturation magnetization decreased in the Co 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ ferrites but increased in the Mn 1-x Ni x Fe₂O₄ ferrite with nickel substitution. The coercivity decreased in the Co 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ ferrites but increased in the Mn 1-x Ni x Fe₂O₄ ferrite with nickel substitution. These variations could thus be explained by using the site distribution equations, particle sizes and spin magnetic moments of the substituted ions.

Crystallographic and Magnetic Properties of Mn x Fe 3-x O 4 Powders

Mn x Fe 3-x O₄ powders have been fabricated by using sol-gel methods; their crystallographic and magnetic properties were investigated by using X-ray diffraction, scanning electron microscopy, Mossbauer spectroscopy, and vibrating sample magnetometer. The Mn x Fe 3-x O₄ ferrite powders annealed at 500 ℃ had a single spinel structure regardless of the Mn²?-doping amount and their lattice constants became larger as the Mn²? concentration was increased. Their Mossbauer spectra measured at room temperature were fitted with 2 Zeeman sextets due to the tetrahedral and octahedral sites of Fe ions, which made them ferrimagnetic. The magnetic behavior of Mn x Fe 3-x O₄ powders showed that the Mn²?-doping amount made their saturation magnetization increase, but there were no severe effects on their coercivities. The saturation magnetization of the Mn x Fe 3-x O₄ powder varied from 38 emu/g to 70.0 emu/g and their minimum coercivity was 111.1 Oe.

Synthesis and Magnetic Properties of Nano-sized Mn Ferrite Powder and Film

Nano-sized manganese ferrite powders and films, MnFe₂O₄, were fabricated by the sol-gel method, and the effects of annealing temperature on the crystallographic and magnetic properties were studied by using X-ray diffractometry, field emission scanning electron microscopy, Mossbauer spectroscopy, and vibrating sample magnetometry. X-ray diffraction spectroscopy of powder samples annealed above 523 K indicated the presence of spinel structure, and the film samples annealed above 773 K also had spinel structure. The particle size increased with the annealing temperature. For the powder samples, the Mossbauer spectra annealed above 573 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of Fe³? ions. Using the Mossbauer subspectrum area ratio the cation distribution could be written as (Mn 0.52 Fe 0.48 ) [Mn 0.48 Fe 1.52 ] O₄. However the spectrum annealed at 523 K only showed as a doublet due to a superparamagnetic phase. As the annealing temperature was increased, the saturation magnetization and the corecivity of the powder samples increased, as did the coercivity of film samples.

Crystallographic and Magnetic Properties of Li 0.7 Co 0.2 Ti 0.2 V 0.2 Fe 1.7 O 4 Ferrite

This study examined the crystallographic and magnetic properties of vanadium-substituted lithium cobalt titanium ferrite, Li 0.7 Co 0.2 Ti 0.2 V 0.2 Fe 1.7 O₄. Ferrite was synthesized using a conventional ceramic method. The samples annealed below 1040 ℃ showed X-ray diffraction peaks for spinel and other phases. However, the sample annealed above 1040 ℃ showed a single spinel phase. The lattice constant of the sample was 8.351 A, which was relatively unaffected by vanadium-substitution. The average grain size after vanadium- substitution was 13.90 ㎛, as determined by scanning electron microscopy. The Mossbauer spectrum could be fitted to two Zeeman sextets, which is the typical spinel ferrite spectra of Fe 3+ with A and B sites, and one doublet. From the absorption area ratio of the Mossbauer spectrum, the cation distribution was found to be (Co 0.2 V 0.2 Fe 0.6 )[Li 0.7 Ti 0.2 Fe 1.1 ]O₄. Vibrating sample magnetometry revealed a saturation magnetization and coercivity of 36.9 emu/g and 88.6 Oe, respectively, which were decreased by vanadium-substitution.

Mössbauer study of Fe‐doped CuGeO3 system Cu0.9Ge0.9Fe0.2O3

The Fe‐doped system Cu0.9Ge0.9Fe0.2O3 has been investigated by means of X‐ray diffractometry, Mössbauer spectroscopy and superconducting quantum interference device. The structure of this system is orthorhombic and the lattice constants are a=4.784 Å, b=8.472 Å and c=2.904 Å, respectively. Magnetic measurements confirm that the spin‐Peierls transition appears in our sample at about 12 K, which is near to the spin‐Peierls transition temperature (Tsp) 14 K of pure CuGeO3 system.The Mössbauer spectrum shows the superposition of two Zeeman sextets and a broad central line due to Fe3+ ions from room temperature to 4.2 K. The Mössbauer parameters show a discontinuity near Tsp. The jump of the magnetic hyperfine field at temperatures lower than Tsp means increasing of the superexchange interaction among the magnetic ions. The jump of the quadrupole splitting and the isomer shift values could be interpreted as due to decrement in symmetry of lattice sites and spontaneous thermal contraction.