• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.33-37
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• 2004

Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ has been studied with Mossbauer spectroscopy, x-ray diffraction, vibrating sample magnetometer (VSM), and magnetoresistance (MR) measurement. The crystal structure was determined to be a cubic spinel with lattice parameter a$_{0}$=9.9880 $\AA$. The MR measurements show a semiconductor behavior below 110 K and metal behaved above 100 K. The temperature dependence of magnetization of Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ was reported. In addition to a large irreversibility between the zero-field-cooling (ZFC) and the field-cooling (FC) magnetization at applied field H=100 Oe, a cusp-like anomaly was observed in both the FC and ZFC curves. It shifted toward the lower temperature region with increasing magnetic field, and then showed convex type maximum at 110 K, under the applied field of 5 kOe. The Mossbauer spectra were measured from 15 K to room temperature. The asymmetric line broadening was observed for the sample Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$, and it was considered to be dynamic Jahn-Teller relaxation. The charge state of Fe ions was ferrous in character. The unusual reduction of magnetic hyperfine field below 110 K was interpreted in terms of cancellation effect between the mutually opposite orbital current field (H$_{L}$) and Fermi contact field (H$_{C}$).

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.219-223
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• 2004

L $i_{0.5}$F $e_{2.5-{\chi}}$R $h_{\chi}$ $O_4$ ($\chi$ = 0.25, 0.50, 0.75, 1.00) has been prepared by solid state reaction. Crystallographic and magnetic properties were investigated by Mossbauer spectroscopy, SQUID magnetometry, and x-ray diffraction. The crystal structure is found to be a cubic spinel structure with space group Fd3m for all the samples. The lattice constant $a_{0}$ increases from 8.3365 $\AA$ to 8.3932 $\AA$ with increasing Rh concentration $\chi$. The migration of Li ion has been confirmed by x-ray patterns and the results of applied field Mossbauer analysis. The temperature dependence of the absorption area of each site was analyzed with the Debye model for the recoil-free fraction. The Debye temperature for the octahedral sites is almost as large as for the tetrahedral sites, thereby suggesting similar inter-atomic binding forces for the octahedral and the tetrahedral sites. The saturated magnetic moment and the Mossbauer spectra taken at 4.2 K under the applied field (6 T) show that the spin structure of L $i_{0.5}$F $e_{2.5-{\chi}}$R $h_{\chi}$ $O_4$ is compatible with the collinear Neel Model.

• Transactions on Electrical and Electronic Materials
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• v.1 no.3
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• pp.29-33
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• 2000

The crystallographic and high frequency characteristics of $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ soft magnetic alloys were investigated under magnetic field annealing, The crystallization fraction of annealed samples with longitudinal magnetic fields is higher than that of samples without magnetic field. When the transverse magnetic field is applied, the crystallization fraction does not increases but decreases until $500^{circ}C$. It is found that for samples, the saturation induction are all same with 1.3 T. The coercive field of as-cast samples is 1.03 A/cm, but in annealed samples it decrease from 0.56 to 0.1A/cm with increasing annealing temperature from 400 to $550^{circ}C$. The squareness of annealed samples under transverse magnetic field has a small value than that of both without field and with longitudinal field annealing. It is noted that the magnetic field annealing with transverse direction to amorphous $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ profoundly influenced on the Mossbauer spectra in contrast to that with longitudinal direction and without magnetic field.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.343-350
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• 1995

An overview will be given on recent Mossbauer and magnetization investigation of the applied field dependence of the magnetic properties of typical systems without strong magnetic anisotropy and showing the absence of magnetic saturation in high fields (including iron-rich spin glass (amorphous $Fe_{93}Zr_{7}$, soft ferromagnets (amorphous $Fe_{88}Zr_{12}$, $Fe_{70}Ni_{20}Zr_{10}$ and $Fe_{88}B_{12}$) and pure Fe). The results emphasize that shape anisotropy due to surface irregularities causes misalignment between the magnetization and the applied field in the otherwise collinear magnetic structure.

• Progress in Medical Physics
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• v.9 no.2
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• pp.73-75
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• 1998

Mossbauer spectroscopy methods are discussed when applied to test the properties of magnetic suppositories used in medicine. The experiments were carried out on magnetic rectal suppositories containing parmadine and fine-dispersed ferrite powder (BaOㆍnFe$_2$O$_3$) as a magnetic filler. According to the data on the value of effective magnetic field on $^{57}$ Fe nuclei in ferrite magnetic sublattices, the stoichiometric n-number equals approximately 5.5; this value corresponds to the composition range of optimal magnetic properties.

• Journal of Magnetics
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• v.1 no.1
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• pp.31-36
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• 1996

An externally applied magnetic field during heat treating the $Nd_2Fe_{14}B/Fe_3B$ based spring magnet was found to enhance the exchange coupling between the hard and soft magnetic grains. More than 30% increase in $M_r/M_s$ values for melt-spun $Nd_2Fe_{73.5}Co_3$$(Hf_{1-x}Ga_x)B_{18.5}$ (x=0, 0.5, 1) alloys was resulted from a uniform distribution of $Fe_3B, \alpha-Fe$ and $Nd_2Fe_{14}B$ phases, and also from a reduced grain size of those phases by 20%. The externally applied magnetic field induced a uniform distribution of fine grains. A study of Mossbauer effect also report that the enhancement of total magnetization of nanocomposite $Nd_2Fe_{14}B/Fe_3B$ alloys is attributed to an increased formation of $Fe_3$B after magnetic annealing.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.14-17
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• 2006

[ $AIFeO_3$ ]has been studied by x-ray diffraction (XRD), vibrating sample magnetometer, Mossbauer spectroscopy. The crystal structure is found to orthorhombic with the lattice parameters being $a_0=4.983\;{\AA},\;b_0=8.554\;{\AA},\;c_0=9.239\;{\AA}$, Magnetic hysteresis curve for $AIFeO_3$ showed weakly ferromagnetic phase at room temperature and a asymmetric shape dependent on the direction of applied field at low temperature. The Curie temperature determined by the temperature dependence of magnetization is 250 K. Mossbauer spectra of $AIFeO_3$ have been taken from 4.2 K to 295 K. Isomer shift at room temperature are found to be $0.11\~0.32\;mm/s$, which is consistent with ferric state. The absorption lines widths become broader with increasing temperature, which is attributed to the Fe ions distribution of each cation site and anisotropy energy difference of each sublattice.

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05a
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• pp.1-1
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• 1992

Shape Memory Alloys have attracted the interest of a great number of researchers in the world, and Mexico is not the exception. Research in this field started ten years ago, and is actually an active line covering the classical Cu-based and Ti-Ni alloys, but also the new Fe-based alloys. Although more basic studies have been performed at the present time, interest for applied research and technological goals is increasing. In this work we present a series of studies carried on these Shape Memory Alloys by the groups in Mexico, and explain what the interest of our groups are in the next future in this are of the Materials Science. Interdisciplinary work has been necessary in the characterization of the different alloys, and multiple techniques have been used, like Mossbauer spectroscopy, thermoelectric power, electron microscopy, ultrasound techniques, neutron and x-ray diffraction, calorimetry, among others. Collaboration With other groups in Europe and in the United States have become highly useful and productive, and some examples of such activities are also reported.

• Journal of Magnetics
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• v.16 no.1
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• pp.27-30
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• 2011

Nano-sized manganese ferrite powders and films, $MnFe_2O_4$, 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, M$\"{o}$ssbauer 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 $Fe^{3+}$ ions. Using the M$\"{o}$ssbauer subspectrum area ratio the cation distribution could be written as ($Mn_{0.52}Fe_{0.48}$) $[Mn_{0.48}Fe_{1.52}]$ $O_4$. 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.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.11-13
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• 2006

[ $M\"{o}ssbauer$ ] spectra of $Ti_{1-x-y}Co_xFe_yO_2(0.01{\leq}x,\;y{\leq}0.05)$ prepared with $^{57}Fe$ enriched iron have been taken at various temperatures ranging from 80 to 300K. The Mossbauer spectrum of $Ti0.94Co_{0.03}Fe_{0.03}O_2$ consists of a ferromagnetic (six-Lorentzian), a paramagnetic phase (doublet) and armorphous phase over all temperature ranges. Isomer shifts indicate $Fe^{3+}$ for the ferromagnetic phase and the paramagneic phase of $Ti_{1-x-y}Co_xFe_yO_2$ samples. It is noted that the magnetic hyperfine field of ferromagnetic phase had the value about 1.5 times as large as that of u-fe. The XRB data for $Ti_{1-x-y}Co_xFe_yO_2$ showed mainly rutile phase with tetragonal structures without any segregation of Co and Fe into particulates within the instrumental resolution limit. The magnetic moment per (Co+Fe) atom in $Ti0.94Co_{0.03}Fe_{0.03}O_2$, under the applied field of 1T was estimated to be about $0.332{\mu}_B$ which is ten times as large as that of $Ti0.97Co_{0.03}Fe_{0.03}O_2,\;0.024{\mu}_B$ per Co atom, suggesting a high spin configuration of Co and fe ions.