Sung Yong An

Mössbauer and magnetic properties of Co–Ti substituted barium hexaferrite nanoparticles

Co–Ti substituted M-type hexagonal barium ferrite nanoparticles BaFe12−2xCoxTixO19 (0⩽x⩽1.0) have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with a Mossbauer spectroscopy, vibrating sample magnetometer, x-ray diffraction (XRD), thermogravimetry (TG), and differential thermal analysis (DTA). The decomposition of amorphous hydroxides in the dried precipitate continued until 570 °C, according to a TG-DTA analysis. The result of XRD measurements shows that the a and c lattice parameters increase with increasing x from a=5.882 and c=23.215 A for x=0.0, to a=5.895 and c=23.295 A for x=1.0. The 57Fe Mossbauer spectra were fitted by a least-squares technique with four subpatterns of Fe sites in the structure and corresponding to the 4f2, 4f1+2a, 12k, and 2b sites. The relative spectra areas of BaFe10CoTiO19 at 295 K were 15%, 30%, 50%, and 5% for 4f2, 4f1+2a, 12k, and 2b subspectra, respectively. The 2b site had a very large quadrupole splitting. The is...

High power ferromagnetic resonance and spin wave instability processes in Permalloy thin films

The high power ferromagnetic resonance (FMR) response, as well as butterfly curves of the spin wave instability threshold microwave field amplitude hcrit versus in-plane static field H profiles, have been measured for Permalloy films with thicknesses of 104, 128, and 270nm at a nominal pumping frequency of 9.37GHz. The hcrit values range from about 1 to 7Oe. Both the resonance saturation response at the FMR field and the subsidiary absorption (SA) response for static fields below the FMR field are similar in appearance to those for bulk ferrites. Butterfly curves over the SA response region, while similar to those for ferrites, exhibit a film thickness dependent band edge cutoff effect not found in bulk ferrites. The SA butterfly curve data were analyzed on the basis of a spin wave instability theory adapted to thin films. The observed shift in the SA band edge cutoff with thickness agrees with calculations based on the thin film dispersion response and the assumption of first order instability processes ...

Magnetic properties of Cr/sup 3+/ substituted BaFe/sub 12/O/sub 19/ powders grown by a sol-gel method

Cr/sup 3+/ substituted Ba-hexaferrite was fabricated by a sol-gel method. The crystallographic and magnetic properties of BaFe/sub 12-x/Cr/sub x/O/sub 19/ (0/spl les/x/spl les/7) were investigated XRD, Rutherford backscattering spectrometry, vibrating sample magnetometry and Mossbauer spectroscopy. The crystal structure was found to be magnetoplumbite, typical of M-type hexagonal ferrite. By substituting Fe/sup 3+/ in BaFe/sub 12/O/sub 19/ by Cr/sup 3+/, we have been able to attribute the Mossbauer parameters to the 5 crystallographic sites of the structure. Only the octahedral sublattices were occupied by Cr ions. The isomer shifts indicate that the valence state of the Fe ions was Fe/sup 3+/. The Curie temperatures of BaFe/sub 12-x/Cr/sub x/O/sub 19/ decreased linearly increasing Cr-substitution, at a rate of 55 K/Cr atom.

Crystallization and Mössbauer studies of melt-spun NdFe10.7TiB0.3Nδ alloys

Magnetic properties of melt-spun NdFe10.7TiB0.3Nδ ribbons have been investigated as functions of quenching rate and nitriding period. NdFe10.7TiB0.3 were prepared with substrate velocity vs⩽18 m/s and were nitrogenated at 500 °C for 15 min. The NdFe10.7TiB0.3Nδ retains the ThMn12-type tetragonal structure with lattice constants a0=8.640 A and c0=4.811 A, but with an increase in the unit cell volume. The NdFe10.7TiB0.3Nδ was confirmed to have uniaxial anisotropy by x-ray diffraction. Mossbauer spectra were taken at various temperatures ranging from 13 to 855 K. The Curie and Debye temperatures are determined to be Tc=833 K and Θ=390 K, respectively. Each spectrum below Tc was fitted with six subspectra of Fe sites (8i1, 8i2, 8j2, 8j1, 8f, and α-Fe). The area fraction of the subspectra at 13 K are 10.2%, 8.2%, 16.5%, 17.5%, 44.3%, and 3.3%, respectively. The magnetic hyperfine fields for the Fe sites decrease in the order, Hhf(8i)>Hhf(8j)>Hhf(8f).

Magnetic properties of helimagnetic YMn2−x(Fe,Co)xO5−δ (0.0⩽x⩽1.0) for the room temperature ferroism

The structural, electrical, and magnetic properties of the YMn2−x(Fe,Co)xO5−δ (0.0⩽x⩽1.0) pseudobinary oxides have been studied utilizing x-ray diffraction, atomic force microscopy, and magnetic measurements. Our interest in these oxides begins with the hypothesis that both ferroelectric and ferromagnetic properties coexist (a condition known as “ferroism or multiferroism”) in these oxides. Pure and (Fe,Co)-doped YMn2O5−δ series have been successfully prepared by means of the sol–gel process. The samples with YMn1.8Fe0.2O5−δ and YMn1.8Co0.2O5−δ composition display a room temperature spontaneous polarization (ferroelectric) and magnetization (ferromagnetic). The ferroism responses in (Fe,Co)-doped YMn2O5−δ series present an opportunity to create and implement spintronics devices that actively couple the ferromagnetic and ferroelectric order parameters.

Magnetic properties of Nd-Ga-Febal-Nb-B alloy

Here, we have synthesized Nd-Ga-Febal-Nb-B alloy by strip casting method. The crystalline and magnetic properties of sample were investigated with x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mossbauer spectrometer. The XRD pattern was analyzed with the Rietveld refinement method, indicating a tetragonal structure and the space group of P42/mnm. The temperature dependence of zero-field cooled (ZFC) magnetization curve was measured under applied field at temperature ranging from 4.2 to 740 K. From the ZFC curve, Curie temperature and spin reorientation temperature are determined to be 615 K and 130 K, respectively. Also, Mossbauer spectra were measured at various temperatures ranging from 4.2 to 620 K. Each spectrum was fitted with 6-sextets for Fe site (8j1, 8j2, 16k1, 16k2, 4c, and 4e), and magnetic hyperfine field, Isomer shift, electric quadrupole shift, and area ratio values were obtained from the fit. We observed the change in slope of magnetic hyperfine field and electric qua...

SYNTHESIS OF Bi-Zn-Al-B-Si-O NANO-GLASS FOR MULTILAYER CHIP INDUCTORS

The ferrite added with Bi-Zn-Al-B-Si-O nano-glass was sintered at 840-900°C, 2 h and the initial permeability, quality factor, density and saturation magnetization of the samples were measured. The initial permeability of the nano-glass added sample was about 62.6 at 0.1 wt%, and showed a sharp increase from 0.4 to 0.5 wt%. Then, it reached a maximum value (211.2) at 1.0 wt% addition. Above 1.0 wt% addition, the initial permeability decreased again with a further increase in the nano-glass content. The quality factor and saturation magnetization of 0.5 wt% nano-glass added NiZnCu ferrites sintered at 880 °C was about 143 and 386 emu/cc, respectively. It was shown that the Bi-Zn-Al-B-Si-O nano-glass systems were useful as a sintering aid in the fabrication of MLCIs.

Crystallization and mossbauer stidies of melt-spun NdFe/sub 10.7/TiB/sub 0.3/N/sub /spl delta// alloys

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