• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.86-89
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• 2007

[ $FeCr_2Se_4$ ] prepared under the high pressure (3 GPa) has been studied with x-ray, neutron diffraction techniques, superconducting quantum interference device (SQUID) magnetometer, resistance, and Mossbauer spectroscopy. The temperature dependence of resistance is explained by Mott-VRH and small polaron model for the regions I (T<20 K) and II (T>42 K), respectively. Neutron diffraction results show an antiferromagnetic spin-lattice coupling near the Neel temperature. So finally the distance of atom is enlarged in region (110$FeCr_2Se_4$ shows convex type of temperature dependence.

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.60-64
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• 2007

Ba-Ferrite single crystals were prepared and characterized by X-ray, SEM and Mossbauer spectroscopy. The single crystal layers was cut in the c-axis and radiated to the surface by ${\gamma}-rays$ for Mossbauer spectroscopy. We found out that the spin states in Fe atoms were parallel to the ${\gamma}-rays$ direction. The temperature dependence of the hyperfine field is almost similar to that of powder samples. The crystal structure is a Magnetoplumbite without any other phases and the lattice parameters are found out with $a_0=5.892{\AA},\;b_0=5.892{\AA},\;c_0=23.198{\AA}$. $M\"{o}ssbauer$ spectrum in single crystal have 5 sets off absorption lines in each Fe site when the ${\gamma}-rays$ have the same radiation direction with the c-axis in the crystal, which mean that the whole crystal bulk formed only one crystal and same spin direction. The hysteresis curve shows the saturation moment and coercive force of 70.71 emu/g and 320 Oe respectively.

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.10-13
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• 2007

Single crystalline, $LuFe_2O_4$, was grown by the floating zone method. The crystal structure was a two-dimensional layered-type rhombohedral($R\={3}mh$) structure, with an $a_0=3.440(2)\;{\AA}\;and\;a\;c_0=25.263(2)\;{\AA}$. The magnetic $N\'{e}el$ temperature($T_N$) was determined to be 250 K. The $M\"{o}ssbauer$ spectrum at 12 K was fitted with four sextet sets which was resulted from the crystal structure. The spectrm at room temperature consisted of three singlets and a doublet with the electric quadrupole splitting. The isomer shift($\delta$) value of the singlet was $0.20{\pm}0.01mm/s$ relative to the Fe metal indicating the $Fe^{3+}$ valence state, and the value of the doublet was $0.70{\pm}0.01mm/s$ indicating $Fe^{2+}$. The $M\"{o}ssbauer$ absorption area ratio between $Fe^{3+}$ and $Fe^{2+}$ at room temperature was 1:1. The doublet phase of spectra gradually disappears by up to 360 K. At 360 K, the spectrum shows the singlet phase. We suggested that the spontaneous polarization effect of $LuFe_2O_4$ was caused by the change of iron behavior.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.92-95
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• 2005

$Zn_{1-x}\;^{57}Fe_xO(x=0.01, 0.02, 0.03)$ compounds were fabricated using the solid-state reaction method. In order to determine magnetic behavior and ionic state of the doped transition metal ($^{57}Fe$) in ZnO, we carried out $M\ddot{o}ssbauer$ measurements at various temperatures ranging from 13 to 295 K. $M\ddot{o}ssbauer$spectra for $Zn_{0.97}\;^{57}Fe_{0.03}O$ at 4.2 K have shown the ferromagnetic phase (sextet), but the only paramagnetic phase (doublet) is seen at 295 K. The hysteresis loop below 77 K for $Zn_{0.97}\;^{57}Fe_{0.03}O$ indicated the coexistence of ferromagnetic and paramagnetic phases.

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.65-70
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• 2007

In this paper, we composed the $LiFePO_4$ for the reversible use as the replacement material of the Li ion batteries and confirmed the good quality of the structure of the samples with the sintering temperature $675^{\circ}C,\;750^{\circ}C,\;and\;800^{\circ}C$ for 30 hours at nitrogen atmosphere. We also investigated the size of the particles through SEM picture and the change of the sintering temperature and the $Fe^{+3}$ content after charging the materials with 1 V, 160 mA and 3 V, 40 mA for 3 hours by Mossbauer spectroscopy. Also we can observe the increase on the $Fe^{+3}$ content at the charge condition and the increase of the amount ratio of the $Fe^{+3}$ ion only in sintering temperature $675^{\circ}C$ according to the increase of the electric charge. We cannot observe the change of the $Fe^{+3}$ ion in sintering temperature $800^{\circ}C$ after charging.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.183-187
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• 2007

Compounds of multiferroic materials $YMn_{2-x}Fe_xO_5$ (x = 0.00, 0.01) were prepared using the sol-gel method. The crystallographic, magnetic and electric properties are studied using x-ray diffraction (XRD), neutron diffraction, vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The crystalline structure of $YMn_2O_5$ was found to be orthorhombic (Pbam) at room temperature. The lattice constants of $YMn_2O_5$ were determined to be $a_0=7.275\;{\AA},\;b_0=8.487\;{\AA},\;c_0=5.674\;{\AA}$. The lattice constants not changed with Fe concentrations. Our data demonstrate the correlation of magnetic and electric properties in $YMn_2O_5$ materials.

• Journal of the Korean Magnetics Society
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• v.18 no.1
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• pp.39-42
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• 2008

[ $AB_2X_4$ ](A, B=Transition Metal, X=O, S, Se) are cubic spinel normal ferrimagnets, in which M ions occupy the tetrahedral sites and Cr ions occupy the octahedral sites. Recently, they have been investigated for behaviour of B site ions and A-B interaction. Polycrystalline $[Co_{0.9}Zn_{0.1}]_A[Cr_{1.98}{^{57}Fe_{0.02}}]_BO_4$ compound was prepared by wet-chemical process. The ferrimagnetic transition was observed around 90K. $M\"{o}ssbauer$ absorption spectra at 4.2K show that the well-developed two sextets are superposed with small difference in hyperfine fields($H_{hf}$). The hyperfine fields of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$ and $Co_{0.9}Zn_{0.1}Cr_{1.98}{^{57}Fe_{0.02}}O_4$ were determined to be 488, 478 kOe and 486, 468 kOe, respectively. We notice that the one of the magnetic hyperfine field values changes with Zn ion substitution. These results suggest the incommensurate states and spin-reorientation temperature($T_S=18K$) changes with Zn ions substitution below spin-reorientation temperature($T_S=28K$) of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$

• Journal of the Korean Magnetics Society
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• v.17 no.1
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• pp.18-21
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• 2007

The hexagonal $HoMn_{1-x}-Fe_xO_3$(x=0.00, 0.05) thin films were prepared using pulsed laser deposition(PLD) method on $Pt/Ti/SiO_2/Si$ substrate. The microstructure and magnetic properties have been studied by x-ray diffraction(XRD), atomic force microscopy (AFH), scanning electron microscope(SEM:), x-ray photoelectron spectroscopy(XPS), and conversion electron $M\"{o}ssbauer$ spectroscopy(CEMS). From the analysis of the x-ray diffraction patterns, the crystal structure for all films was found to be a hexagonal($P6_3cm$), which was preferentially grown along(110) direction. The lattice constant $c_0$ of the film with x=0.05 was close to that of single crystal, whereas lattice constant $a_0$ with respect to single crystal shows a slight decrease. This difference of lattice parameters between film and single crystal was caused by the lattice mismatch between the film and $Pt/Ti/SiO_2/Si$ substrate. Conversion electron $M\"{o}ssbauer$ spectrum of $HoMn_{0.95}Fe_{0.05}O_3$ thin film shows an asymmetry doublet absorption ratio at room temperature, which is due to the oriented direction of crystallographic domains. This is corresponding with analysis of x-ray diffraction. The quadrupole splitting(${\Delta}E_Q$) at room temperature is found to be $1.62{\pm}0.01mm/s$. This large ${\Delta}E_Q$ was caused by asymmetry environment surrounding Fe ion.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.864-873
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• 1995

Amorphous $Fe_{73.5}Cu_{1}Nb_{3}Si_{16.5}B_{6}$ ribbons were annealed for different time at $500^{\circ}C$ and $552^{\circ}C$, just before and after the exothermic reaction in DSC curve. The development of nanocrystalline phase was investigated by means of $M\"{o}ssbsuer$ spectroscopy. The crystalline phase consists mainly of $DO_{3}Fe-Si$. Though slight in amount (5%), another ferromagnetic phase which could be presumed $t-Fe_{3}B$ was detected Si content of $DO_{3}Fe-Si$, Si/(Fe+Si), was 0.218 under the heat treatment at $500^{\circ}C$ for 60 min and 0.222 at $552^{\circ}C$ for 10 min. Since then both of those values decreased with time until 120 min and finally these two values remained constant at 0.210. The variation in Si content with annealing time results in the variation in the hyperfine field and the isomer shift. The increase in the mean hyperfine fields and the decrease in the mean isomer shifts of Fe-Si are caused by the increase in Si content. The volume fractions of residual amorphous phase rapidly decrease during the early stage of annealing and come nearer to saturation after 120 min both at $500^{\circ}C$ and $552^{\circ}C$. The decrease in the mean hyperfine field of residual amorphous. in spite of slight changes in the volume fractions of Fe-Si and of residual amorphous after 120 min. is caused by the increase in the content of Nb and B in residual amorphous phase. The saturated volume fraction of the crystalline phase was 81% for $500^{\circ}C$ (180 min) and 77% for $552^{\circ}C$ (960 min), different from expectation.

• Journal of the Korean Magnetics Society
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• v.13 no.6
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• pp.237-242
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• 2003

$Ti_{1-x}$$^{57}$ F $e_{x}$ $O_2$(0.0$\leq$x$\leq$0.07) compounds were fabricated using the sol-gel method, and the crystal structure and magnetic properties were investigated as a function of doped $^{57}$ Fe concentration. X-ray diffraction patterns showed a pure anatase single phase, without any segregation of Fe into particulate. With varying $^{57}$ Fe concentration, we could observe unusual magnetic phenomena in these materials. Doping $^{57}$ Fe into the Ti $O_2$ nonmagnetic semiconductor formed magnetic properties, but the gradual increase of $^{57}$ Fe concentration decreased rapidly the ferromagnetic properties rather than enhanced the ferromagnetic properties. Obvious ferromagnetic behavior was shown for the samples with x$\leq$0.01, while paramagnetic behavior was shown for the sample with x$\geq$0.03. These phenomena could be verified using Mossbauer measurement. Separation of the ferromagnetic phase (sextet) and the paramagnetic phase (doublet) of the samples with different $^{57}$ Fe concentration was characterized. Samples with x$\leq$0.01 have sextet and doublet simultaneously, but samples with x$\geq$0.03 have only doublet at room temperature. This indicates that the sample x$\leq$0.01 have the ferromagnetic phase at room temperature. This result corresponded with the M-H loops referenced above and reveals an interesting feature that there is a critical limit of $^{57}$ Fe concentration (0.01$\leq$0.01 samples was fundamentally attributable to the paramagnetic phase as well as the ferromagnetic phase.e.