• Journal of the Korean Magnetics Society
• /
• v.15 no.2
• /
• pp.106-108
• /
• 2005

The rutile polycrystal $Ti_{0.99}\;^{57}Fe_{0.01}O_2$ prepared with $^{57}Fe$ enriched iron have been studied by $M\ddot{o}ssbauer$ spectroscopy, X-ray diffraction and VSM. The $M\ddot{o}ssbauer$ spectrum of $Ti_{0.99}\;^{57}Fe_{0.01}O_2$ consists of a ferromagnetic and a paramagnetic phase over all temperature ranging from 4 to 300 K. Isomer shifts indicate $Fe^{2+}$ for the ferromagnetic phase, but $Fe^{3+}$ for the paramagneic phase of $Ti_{0.99}\;^{57}Fe_{0.01}O_2$ sample. It is noted that the magnetic hyperfine field of ferromagnetic phase had the value about 1.48 times as large as that of $\alpha$-Fe. The XRD data for $Ti_{0.99}\;^{57}Fe_{0.01}O_2$ showed a pure rutile phase with tetragonal structures without any segregation of Fe into particulates within the instrumental resolution limit The magnetic hysteresis (M-H) curve at room temperature showed an obvious ferromagnetic behavior and the magnetic moment per Fe atom under the applied field of 1 T was estimated to be about $0.71{\mu}_B$, suggesting a low spin configuration of Fe ions.

• Journal of the Korean Magnetics Society
• /
• v.15 no.2
• /
• pp.137-141
• /
• 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 $Cu_xFe_{1-x}Cr_2S_4$.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1997.06a
• /
• pp.253-259
• /
• 1997

The iron doped GaAs single crystals were grown by liquid phase epitaxial method and its some physical properties were evaluated with a view to investigate the crystal quality and emission property. The isomer shift of 0.303mm/sec is calculated from low-temperature M ssbauer spectroscopy and we know that charge state of iron ion is 3+ in GaAs crystal. In low temperature photoluminescence, the deep emission bands with wide-line width have been observed at 0.99eV and 1.15eV in addition to sharp excitonic peaks. We attributed that these deep emissions are originated from substitutional Fe-acceptor which has charge state of 3+ and 2+, respectively.

• Journal of the Korean Magnetics Society
• /
• v.15 no.2
• /
• pp.100-105
• /
• 2005

$Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticles have been prepared by a sol-gel method. The structural and magnetic properties have been investigated by DTA/TGA, XRD, SEM, and $M\ddot{o}ssbauer$ spectroscopy, VSM. $Ni_{0.9}Zn_{0.1}Fe_2O_4$ powder that was annealed at $300^{\circ}C$ has spinel structure and behaved superparamagnetically. The estimated size of superparammagnetic Ni-Zn ferrite nanoparticle is around 10 nm. The hyperfine fields at 13 K for the A and B patterns were found to be 533 and 507 kOe, respectively. The blocking temperature ($T_B$) of superparammagnetic $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle is about 250 K. The magnetic anisotropy constant and relaxation time constant of $Ni_{0.9}Zn_{0.1}Fe_2O_4$ nanoparticle were calculated to be $1.6\times10^6\;ergs/cm^3$ and ${\tau}_0=5.0{\times}10^{-13}$ s, respectively. Also, Temperature increased up to $43^{\circ}C$ within 10 minutes under AC magnetic field of 7 MHz. It is considered that $Ni_{0.9}Zn_{0.1}Fe_2O_4$ powder that was annealed at $300^{\circ}C$ is available for biomedicine application such as hyperthermia, drug delivery system and contrast agents in MRI.

• Journal of the Korean Magnetics Society
• /
• v.15 no.2
• /
• pp.81-84
• /
• 2005

The origin for the charge disproportionation (CD) transition in polycrystalline $La_{1/3}Sr_{2/3}FeO_{2.96}$ was examined using X-ray diffraction and the external field $M\ddot{o}ssbauer$ssbauer spectroscopy. In order to see how the external magnetic field affects the CD state above its transition temperature, an external magnetic field of up to 6 T was applied either parallel or perpendicular to the $\gamma-ray$ direction with the sample temperature fixed at 225 K, which was above the CD transition temperature. Without an external magnetic field, a completely paramagnetic singlet was obtained in the temperature range of the averaged valence state above the transition temperature, which was interpreted as coming from the average valence $Fe^{3.6+}$. In the longitudinal geometry, a magnetic Zeeman with its intensity ratio 3:0:1:1:0:3 is superimposed to the central singlet. In the transverse geometry, however, the central singlet disappears and only a magnetic component with its intensity ratio 3:4:1:1:4:3 emerges. The existence of a singlet is understood as an evidence of the fast electron-transfer among Fe ions. Since the singlet still exists under the magnetic field, the application of an external field has little effect on the conduction mechanism of hopping electrons.

• Journal of the Korean Magnetics Society
• /
• v.8 no.2
• /
• pp.67-73
• /
• 1998

Crystallographic and magnetic properties of perovskite $Gd_{1-x}Sr_xFeO_{3-y}$ (x=0.0, 0.5) substituted $Sr^{2+}$ having larger inoic radius than $Gd^{3+}$ at GdFeO$_3$have been studied by x-ary diffraction, M$\ "{o}$ssbauer spectroscopy, and VSM. The cystal structures are found to be orthorhombic with the lattice parameters : $a_o=5.53\;{\AA},\;b_o=5.608\;{AA},\;C_o=7.724\;{\AA}$ for $Gd_{0.5}Sr_{0.5}FeO_{3-y}$ (x=0.0, 0.5) have been investigated over temperature range from 4.2 to 690 K using the M$\ "{o}$ssbauer technique. The Neel temperatuer of $Gd_{1-x}Sr_xFeO_{3-y}$ system is 690 K with x value of 0.0 and 515 K with x value of 0.5. Analysis of M$\ "{o}$ssbauer spectra Mohr's salt analysis for $Gd_{1-x}Sr_xFeO_{3-y}$ demonstrated the existence of the mixed valence states of iron and the coordination state of $Fe^{3+}$ and $Fe^{4+}$ ions. The Corresponding hyperfine parameters for GdFeO$_3$ are compatible with S=5/2 $Fe^{3+}$ in octahedral cooedination.l cooedination.

• Journal of the Korean Magnetics Society
• /
• v.16 no.6
• /
• pp.287-292
• /
• 2006

Al substituted $CoAl_{0.5}Fe_{1.5}O_{4}$ has been studied with x-ray and neutron diffraction, $M\"{o}ssbauer$ spectroscopy and magnetization measurements. $CoAl_{0.5}Fe_{1.5}O_{4}$ revealed a cubic spinel structure of ferrinmagnetic long range ordering at room temperature, with magnetic moments of $Fe^{3+}(A)(-2.29{\mu}_{B}),\;Fe^{3+}(B)(3.81\;{\mu}_{B}),\;Co^{2+}(B)(2.66{\mu}_{B})$, respectively. The temperature dependence of the magnetic hyperfine field in $^{57}Fe$ nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the $N\'{e}el$ theory of magnetism. In the sample of $CoAl_{0.5}Fe_{1.5}O_{4}$, the interaction A-B interaction and intrasublattice A-A superexchange interaction were antiferromagnetic with strengths of $J_{A-B}=-19.3{\pm}0.2k_{B}\;and\;J_{A-A}=-21.6{\pm}0.2k_{B}$, respectively, while the intrasublattice B-B superexchange interaction was found to be ferromagnetic with a strength of $J_{B-B}=3.8{\pm}0.2k_{B}$.

• Journal of the Korean Magnetics Society
• /
• v.19 no.3
• /
• pp.113-119
• /
• 2009

$^{57}Fe_xCu_{1-x}O$(x = 0.0, 0.02) powders were prepared by sol-gel method and their crystallographic and magnetic hyperfine properties have been studied using X-ray diffraction and $M{\ddot{o}}ssbauer$ spectroscopy (MS). The crystal structure of the samples is found to be monoclinic without any secondary phases and their lattice parameters increase with increasing annealing temperature ($T_A$), which is attributed to an increase in oxygen-vacancy content. MS measurements at room temperature indicate that $Fe^{3+}$ ions substitute $Cu^{2+}$ sites and ferromagnetic phase grow with increasing $T_A$. Magnetic hyperfine and quadrupole interactions of $^{57}Fe_{0.02}Cu_{0.98}O$ ($T_A=500^{\circ}C$) in the antiferromagnetic state at 17 K have been studied, yielding the following results: $H_{hf}=426.94\;kOe$, ${\Delta}E_Q=-3.67\;mm/s$, I.S.=0.32 mm/s, ${\theta}=65^{\circ}$, ${\phi}=0^{\circ}$, and ${\eta}=0.6$.

• Resources Recycling
• /
• v.13 no.5
• /
• pp.45-50
• /
• 2004

To investigate the characteristics of phases formed in iron carbides, super iron carbide was synthesized from hematite fines with $CO-H_2$ gas mixture after reduction under $H_2$ gas at $600^{\circ}C$. Before carburization, the surface of iron powder reduced was pre-treated in the atmosphere of 0.05 vol% $NH_3$-Ar. The synthesized iron carbides were comprehensively explored by C/S analyzer(Low C/S determinator), M$\"{o}$ssbauer spectroscopy, X-ray diffraction patterns(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and Raman spectroscopy at various reaction time of 5, 10, 15, 20, 25, 30, and 35 min, respectively. By adding a small amount of $NH_3$ gas, the super iron carbides containing 10 wt% carbon were synthesized, and its addition stabilized iron carbides. It was found that the $NH_3$ treatment played a major role in the formation of iron carbide without decomposition($Fe_3C{\to}$3Fe+C) of iron carbides and precipitation of free carbon. It also succeed to synthesize super iron carbide, $Fe_5C_2$, as a stable single phase without involving Fe and $Fe_3C$ phases.

• Journal of the Korean Magnetics Society
• /
• v.15 no.3
• /
• pp.172-176
• /
• 2005

Four nano-sized Fe-nano particle samples synthesized by Chemical Vapor Condensation (CVC) were analyzed using $M\ddot{o}ssbauer$ spectroscopy, XRD, BET and TEM. The samples were consisted as functions of carrier gas and decomposition temperature. The synthesized nanoparticles consisted of two- or three-layers with the circular shape. The average particle size was increased with increasing the decomposition temperature. At $500^{\circ}C$ for the decomposition temperature, $Fe_3C$ was formed more under the environment of CO carrier gas than that of $CH_4$. However, at $1,100^{\circ}C$, almost of Fe-nano particles were transformed into $Fe_3C$ with using both carrier gas.