• Journal of the Korean Chemical Society
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• v.56 no.5
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• pp.609-616
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• 2012

Ba-ferrite ($BaFe_{12}O_{19}$) nanoparticles were synthesized by chemical coprecipitation method in an aqueous solution. The particle size and the crystallization temperature of the Ba-ferrite nanoparticles were controlled varying the precipitation temperature. The precipitate that was prepared at $0^{\circ}C$ showed the crystal structure of Ba-ferrite in X-ray diffraction when it was calcined at the temperature above $580^{\circ}C$, whereas what was prepared at $50^{\circ}C$ showed the crystallinity when it was calcined at the temperature higher than about $700^{\circ}C$. The particle sizes of the synthesized Ba-ferrite were in a range of about 20-30 nm when it was prepared by being precipitated at $0^{\circ}C$ and calcined at $650^{\circ}C$. When the precipitation temperature increased, the particle size also increased even at the same calcination temperature. The magnetic properties of the Ba-ferrite nanoparticles were also controlled by the synthetic condition of precipitation and calcination temperature. The coercive force could be appreciably lowered without a loss of saturation magnetization when the Ba-ferrite nanoparticles were prepared by precipitation and calcination both at low temperatures.

• Journal of Magnetics
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• v.9 no.2
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• pp.27-33
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• 2004

Magnetic properties of $Nd_4Fe_{77.5}B_{18.5}$ compound in term of exchange coupling between $Nd_2Fe_{14}B$ and $Fe_3B$ magnetic nano crystals in melt spun powders were characterized by varying the quenching speed in mass production line. The exchange coupled phenomenon was characterized as functions of nano crystal size and volume fraction of each magnetic phase which was possible by employing Henkel plot (${\delta}M$) and refined Mossbauer spectroscopy. The optimized magnetic properties obtained from the present volume production line were: $B_r= 11.73 kG,{_i}H_c/ = 3.082 kOe$, and $(BH)_{max} = 12.28 MGOe.$ The volume fraction of each magnetic phase for those conditions giving the grain size of 10 nm were ${\alpha}-Fe; 4.2%, Fe_3B; 60.1 %$, and $Nd_2Fe_{14}B; 35.7%$. The superior magnetic properties in the $Nd_2Fe_{14}Fe_3B$ based nanocomposites were confirmed to be dependant on the volume fraction of $Fe_3B$.

• Korean Journal of Materials Research
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• v.15 no.6
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• pp.393-398
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• 2005

The crystal structure and magnetic properties of the $Mg_{1-x}Zn_xFeAlO_4\;(0{\leq}x\leq1.0)$ have been investigated by means of x-ray diffractometry and $M\ddot{o}ssbauer$ spectroscopy. The samples$(0{\leq}x\leq1.0)$ have been prepared by the ceramic sintering method. The x-ray diffraction pattern shows that the crystal structure of the samples is a cubic spinel type. The lattice constant has been found by extrapolation using the Nelson-Riley function and it increases slightly from $8.3496\AA\;to\;8.4128\AA$ with Zn concentration. The $M\ddot{o}ssbauer$ spectra for x<0.4 show a superposition of two sextets ana a paramagnetic doublet at room temperature. The superparamagnetic doublet for x<0.4 seems to be due to Al ion in tetrahedral site by the superparamagnetic clustering effect.

• Journal of Magnetics
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• v.7 no.2
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• pp.40-44
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• 2002

Crystallographic and magnetic properties of ;$LaFe_{1-x}Ga_xO_3$($\chi$= 0, 0.1, 0.3, 0.5, and 0.7) were studied using XRD and Mossbauer spectroscopy. The crystal structures were found to be orthorhombic and the lattice parameters $\alpha$, b, and c were found to decrease with increasing Ga substitution. M$\ddot{o}$ssbauer spectra were obtained at various absorber temperatures ranging from 20 K to 750 K. The M$\ddot{o}$ssbauer spectra were all sextets below $T_N$ and were all singlets above $T_N$. Asymmetric broadening of the M$\ddot{o}$ssbauer spectral lines at 20 K was explained by the multitude of possible environments for an iron nucleus. As the temperature increases to $T_N$, a systematic line broadening in M$\ddot{o}$ssbauer spectra was observed and interpreted to originate from different temperature dependencies of the magnetic hyperfine fields at various iron sites.

• Bulletin of the Korean Chemical Society
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• v.15 no.7
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• pp.541-545
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• 1994

A series of samples of the ${Ca_xEu_{1-x}FeO_{3-y}$ (x=0.00, 0.25, 0.50, 0.75, and 1.00) system has been prepared at $1,250^{\circ}C$ under an atmospheric air pressure. X-ray diffraction analysis of the solid solution assigns the structure of the compositions of x=0.00, 0.25, 0.50, and 0.75 to the orthoferrite-type orthorhombic system, and that of x=1.00 to the brownmillerite-type orthorhombic one. The mole ratios of $Fe^{4+}$ ion in the solid solutions or ${\tau}$ values were determined by the Mohr's salt analysis and nonstoichiometric chemical formulas of the system were formulated from x, ${\tau}$, and y values. From the result of the Mossbauer spectroscopy, the coordination and magnetic property of the iron ion are discussed. The electrical conductivities are measured as a function of temperature. The activation energy is minimum at the composition of x=0.25. The conduction mechanism can be explained by the hopping of electrons between the mixed valences of $Fe^{3+}\;and\;Fe^{4+}$ ions.

• Bulletin of the Korean Chemical Society
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• v.15 no.8
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• pp.636-640
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• 1994

The nonstoichiometric perovskite solid solutions of the $Nd_{1-x}Sr_xFeO_{3-y}$ system for the compositions of x=0.00, 0.25, 0.50, 0.75, and 1.00 have been prepared at $1150^{\circ}C$ in the air pressure. The compound of x=0.00, NdFe$O_{3.0}$, contains only $Fe^{3+}$ ion in octahedral site and the others involves the mixed valence state between $Fe^{3+}$ and $Fe^{4+}$ ions. The mole ratio of $Fe^{4+}$ ion or the ${\tau}$-value increases steadily with the x-value and then is maximized at the compositionof x= 1.00. The nonstoichiometric chemical formulas of the system are formulated from the x, ${\tau}$ and y values. From the Mossbauer spectroscopy, the isomer shift of $Fe^{3+}$ ion decreases with the increasing x-value, which is induced by the electron transfer between the$Fe^{3+}$ and $Fe^{4+}$ ions. The transfer is made possible by the indirect interaction between $Fe^{3+}$ and$Fe^{4+}$ ions via the oxygen ion. The eg electrons of the$Fe^{3+}$ ions are delocalized over all the Fe ions. Due to the electron transfer, the activation energy of electrical conductivity is decrease with the increasing amount of $Fe^{4+}$ ion.

• Journal of the Korean Magnetics Society
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• v.11 no.1
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• pp.21-25
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• 2001

$\alpha$-Fe$_2$O$_3$ thin films were prepared on Si substrate by a pulsed laser deposition system and characterized by X-ray and Mossbauer spectroscopy. The appropriate conditions of pulsation was the power of 5.128 W/cm2 at on oxygen pressure of 0.1 Torr at a substrate temperature of 30$0^{\circ}C$. After that the film was heated at 80$0^{\circ}C$ for 1 day. The particles shape deposited on the film was ellipsoidal and the average length and width were 200~300 nm, 70~150 am respectively. The crystal structure was conformed to be of corundums symmetry with the hexagonal unit cell having a lattice constant of u = 5.03$\pm$0.05 $\AA$, c = 13.735$\pm$0.05 $\AA$. The average angles between the atomic spin and the magnetic hyperfine field of Fe ion were 38$^{\circ}$and 48$^{\circ}$ at above and blow the Morin transition temperature respectively. The Morin transition was found to occur at the temperature ranges from 200 K to room temperature and atomic spin direction was assumed to change from 48$^{\circ}$ to 80$^{\circ}$in respect to the c-axis.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.113-117
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• 2005

Multiferroic $HoMnO_3$ single crystal was prepared using 4-point focused floating zone furnace, and polycrystalline $HoMn_{1-x}\;^57Fe_xO_3$ (x=0.00, 0.01, 0.02, 0.05) powders have been prepared by solid state reaction. Their magnetic and crystallographic properties are studied using MPMS, PPMS, and $M\ddot{o}ssbauer$ spectroscopy. The crystal structure found to be a hexagonal and a magnetic easy-axis is (110) direction. As the external applied magnetic field increases, temperature of the dielectric constant anomaly is decreased. $HoMn_{0.95}\;^{57}Fe_{0.05}O_3$ shows huge quadrupole splitting value from the $M\ddot{o}ssbauer$ spectra.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.137-141
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• 2005

The CMR properties and magnetic properties of sulphospinels $Zn_xFe_{1-x}Cr_2S_4$ have been explored by X-ray diffraction, magnetoresistance measurement, and $M\ddot{o}ssbauer$ spectroscopy. The crystal structures in the range of x=0.05, 0.1, 0.2 are cubic at room temperature. Magnetoresistance measurement indicates that these system is semiconducting below about 160 K. The temperature of maximum magnetoresistance is almost consistent with Curie temperature. The Zn substitutions for Fe occur to increase the Jahn-Teller relaxation and the electric quadrupole shift. CMR properties could be explained with Jahn-Teller effect, and half-metallic electronic structure, which is different from both the double exchange interactions of manganite La-Ca-Mn-O system and the triple exchange interactions of chalcogenide $Cu_xFe_{1-x}Cr_2S_4$.

• Journal of the Korean Magnetics Society
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• v.23 no.2
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• pp.43-48
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• 2013

The Jahn-Teller distortion of chalcogenide $Fe_{0.9}M_{0.1}Cr_2S_4$ (M=Co, Ni, Zn) have been investigated by M$\ddot{o}$ssbauer spectroscopy. The crystal structures of $Fe_{0.9}M_{0.1}Cr_2S_4$ (M=Co, Ni, Zn) are cubic spinel at room temperature. Magnetoresistance measurements indicate these system is conducting-semiconducting transistion around $T_C$. Below $T_C$, the asymmetric line broadening is observed and considered to be dynamic Jahn-Teller distortion. Isomer shift value of the samples at room temperature was about 0.5 mm/s, which means that charge state of Fe ions is ferrous in character. The Ni substitutions for Fe occur to increase the Jahn-Teller relaxation. CMR properties could be explained with magnetic polaron due to Jahn-Teller effect, which is different from both the double exchange interactions of manganite system and the triple exchange interactions of chalcogenide $Cu_xFe_{1-x}Cr_2S_4$.