Kwang Pyo Chae

Crystallographic and magnetic properties of CoCrxFe2−xO4 ferrite powders

Abstract The CoCr x Fe 2− x O 4 (0.0⩽x⩽1.0) ferrite powders are fabricated by a sol–gel method. The crystallographic and magnetic properties of powders are investigated by X-ray diffraction (XRD), Mossbauer spectroscopy, scanning electron micrography (SEM) and vibrating sample magnetometer (VSM). The structures are spinel, and the lattice constants and the size of particle decrease with increasing Cr contents in CoCr x Fe 2− x O 4 . The Mossbauer spectra, consisted of two Zeeman sextets (0.0⩽ x ⩽0.6) due to Fe 3+ ions at tetrahedral and octahedral sites, changed gradually to doublet (0.8⩽ x ⩽1.0) at room temperature. The variation of Mossbauer parameters has been discussed with the crystallographic and magnetic properties of powders. The magnetic hyperfine fields and the Neel temperature decrease with increasing Cr contents. The coercivity decreases fast but the saturation magnetization slowly decreases with increasing x in CoCr x Fe 2− x O 4 .

Mössbauer study of Fe2O3(Al2O3)x(CuO)1-x system

Abstract The Fe 2 O 3 (Al 2 O 3 ) x (CuO) 1-x system (0.0≤x≤0.8) has been investigated in the range of 0.0≤x≤0.8 by means of X-ray diffractometry and Mossbauer spectroscopy. The structure of the system is a cubic spinel type although it is strongly nonstoichiometric in the entire composition range. A pair of well defined Zeeman splittings from Fe 3+ ions at A- and B-sites for x=0.0, and three Zeeman lines from Fe 3+ ions at A- and B-sites and Fe 2+ ions at B-sites for x ranging from 0.2 to 0.8 have been observed at room temperature. The observed hyperfine fields and Neel temperatures could be explained on the basis of the superexchange and supertransferred hyperfine interactions.

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.

Mössbauer study of Y3-xFe5+xO12 and Y3-xInxFe5O12 (x=0.0, 0.18, 0.33) system

Abstract The Y 3−x Fe 5+x O 12 and Y 3−x In x O 12 systems have been investigated by means of X-ray diffractometry and Mossbauer spectroscopy. From the X-ray diffraction analysis, the specimens have been found to be of the garnet structure in the entire composition range. The Mossbauer spectrum for x=0.0 at room temperature consists of two Zeeman sextets, one due to the Fe 3+ on octahedral sites and the other due to the Fe 3+ on tetrahedral sites, respectively. However, in the range between x=0.18 and 0.33, the spectra show four Zeeman sextets which could be assigned to two octahedral sites and two tetrahedral sites.

Crystallographic and Magnetic Properties of Nickel Substituted Manganese Ferrites Synthesized by Sol-gel Method

Nickel substituted manganese ferrites, Mn 1-x Ni x Fe₂O₄ (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 Fe₂O₄ ferrite sintered above 523 K indicated a spinel structure; particles increased in size with hotter sintering. The Mossbauer 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 Fe₂O₄ ferrite sintered at 773 K were 53.05 emu/g and 142.08 Oe. In Mn 1-x Ni x Fe₂O₄ (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 Mossbauer spectra could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and the octahedral sites of the Fe³? ions. The variations of saturation magnetization and coercivity with changing Ni content could be explained using the changes of particle size.

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.

Crystallographic and Magnetic Properties of Nano-sized Nickel Substituted Cobalt Ferrites Synthesized by the Sol-gel Method

Nano-sized nickel substituted cobalt ferrite powders, Ni x Co 1-x Fe₂O₄ (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 Mossbauer absorption spectra of NixCo1-xFe2O4 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 Fe₂O₄. This could be explained using the cation distribution, which can be written as, (Co 0.28-0.28x Fe 0.72+0.28x )[Ni x Co 0.72-0.72x Fe 1.28-0.28x ]O 4 . 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.

Magnetic Properties of Ti-Doped Ultrafine CoFe2O4 Powder Grown by the Sol Gel Method

Ultrafine Ti-doped CoFe2O4 powders, Ti0.2Co1.2Fe1.6O4, are fabricated by the sol gel method and their magnetic and crystallographic properties depending on annealing temperature are investigated by X-ray diffractometer, Mössbauer spectroscopy, and a vibrating sample magnetometer. With X-ray diffraction and Mössbauer spectroscopy measurements, the formation of nanocrystallized particles is confirmed when Ti0.2Co1.2Fe1.6O4 ferrite is annealed at 473 K. The samples annealed between 673 and 773 K, show that the ferrimagnetic phase and paramagnetic phase coexist. That is, the sample annealed at 673 K has the 18% ferrimagnetic phase, and the sample annealed at 773 K has the 88% ferrimagnetic phase. But the samples annealed at and above 873 K have only a single-phase spinel structure and behave ferrimagnetically. The Néel temperature of our sample is 643 K, which is lower than that of pure cobalt ferrite powder. The magnetic behaviour of Ti0.2Co1.2Fe1.6O4 powder shows that an increase in the annealing temperature yields a decrease in the coercivity and, in contrast, an increase in the saturation magnetization. The maximum coercivity and the saturation magnetization of Ti0.2Co1.2Fe1.6O4 ferrite powder are 1.56 kOe and 62.6 emu/g, respectively.

Cation distribution of indium‐substituted garnet, Y2.4In0.6Fe5O12

The cation distribution of the Y2.4In0.6Fe5O12 system has been studied by means of Mossbauer spectroscopy and x‐ray diffractometry. The structure of the system is yttrium‐iron‐garnet structure with a lattice constant of 12.387 A. Four Zeeman lines from Fe3+ ions at the a,a’ and d,d’ sites have been observed at room temperature. Using the temperature dependence of the absorption area of Mossbauer line and the results of x‐ray diffractometry, the cation distribution of the system can be written as {Y2.4In0.6Feα−β}(Fe2−α) [Fe3+β]O12.

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.