In-Bo Shim

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...

Lanthanide(III)-Doped Magnetite Nanoparticles

Nearly monodisperse lanthanide-doped magnetite nanoparticles were obtained by thermally decomposing a mixture of Fe(acac)(3) and Ln(acac)(3) (acac = acetylacetonate; Ln = Sm, Eu, Gd) in the presence of passivating surfactants. Magnetic studies revealed room-temperature ferromagnetic behaviors of these doped nanoparticles, distinctly different from those of the undoped parent magnetite or the doped nanoparticles prepared by a coprecipitation method.

Directing the Deposition of Ferromagnetic Cobalt onto Pt-tipped CdSe@CdS Nanorods: Synthetic and Mechanistic Insights

A methodology providing access to dumbbell-tipped, metal-semiconductor and metal oxide-semiconductor heterostructured nanorods has been developed. The synthesis and characterization of CdSe@CdS nanorods incorporating ferromagnetic cobalt nanoinclusions at both nanorod termini (i.e., dumbbell morphology) are presented. The key step in the synthesis of these heterostructured nanorods was the decoration of CdSe@CdS nanorods with platinum nanoparticle tips, which promoted the deposition of metallic CoNPs onto Pt-tipped CdSe@CdS nanorods. Cobalt nanoparticle tips were then selectively oxidized to afford CdSe@CdS nanorods with cobalt oxide domains at both termini. In the case of longer cobalt-tipped nanorods, heterostructured nanorods were observed to self-organize into complex dipolar assemblies, which formed as a consequence of magnetic associations of terminal CoNP tips. Colloidal polymerization of these cobalt-tipped nanorods afforded fused nanorod assemblies from the oxidation of cobalt nanoparticle tips at the ends of nanorods via the nanoscale Kirkendall effect. Wurtzite CdS nanorods survived both the deposition of metallic CoNP tips and conversion into cobalt oxide phases, as confirmed by both XRD and HRTEM analysis. A series of CdSe@CdS nanorods of four different lengths ranging from 40 to 174 nm and comparable diameters (6-7 nm) were prepared and modified with both cobalt and cobalt oxide tips. The total synthesis of these heterostructured nanorods required five steps from commercially available reagents. Key synthetic considerations are discussed, with particular emphasis on reporting isolated yields of all intermediates and products from scale up of intermediate precursors.

Growth of ferromagnetic semiconducting cobalt-doped anatase titanium thin films

Heteroepitaxial and polycrystalline anatase Ti1−xCoxO2 (0.0⩽x⩽1.0) thin films were prepared by soft chemical processing on LaAlO3 (001) and thermally oxidized silicon substrates and the crystallinity and magnetic properties were investigated. X-ray diffraction (XRD) spectrum of the Ti1−xCoxO2 films on LaAlO3 (001) substrate shows (004) and (008) peaks of heteroepitaxy anatase without any impurity phase. The full-width at half maximum of the (004) peak rocking curve is 0.4°. The XRD patterns of thin films deposited on the SiO2/Si(001) substrate are anatase type polyscrystalline structure. Microstructural characterization on Ti1−xCoxO2 thin film employing atomic force microscope showed island type grains in 20 nm in size and the surface roughness of typical thin films was 1.5 nm. Sharp hysteresis loops, indicating a well-ordered ferromagnetic structure, appeared in the magnetization versus magnetic field curves when the magnetic field was applied in the plane of the film. This result clearly indicates that ...

Preparation of Ba-ferrite containing glass-ceramics in BaO–Fe2O3–SiO2

Abstract Ba-ferrite (BaFe 12 O 19 ) containing glass-ceramics have been prepared from the glass in BaO–Fe 2 O 3 –SiO 2 through a novel 2 step crystallization method in order to manufacture the magnetic memory disk without deformation. It is revealed that the glass pre-crystallized prior to secondary crystallization shows no shape deformation during heat-treatment and also exhibits better magnetic properties compared with the conventional 1 step crystallized glass.

Mossbauer studies of /sup 57/Fe-doped anatase TiO/sub 2/

In this paper, the magnetic properties of /sup 57/Fe-doped TiO/sub 2/ with varying /sup 57/Fe contents were studied. In order to determine magnetic behavior and ion state of doped transition metal (/sup 57/Fe) in TiO/sub 2/, Mossbauer studies were carried out.

Easy synthesis and characterization of γ‐Fe2O3 nanoparticles for biomedical applications

Easy syntheses of γ‐Fe2O3 nanoparticles have been fabricated by the sol–gel method. The powders present average particle size of 7, 10, and 13nm with narrow size distribution for samples as-obtained and annealed at 150, 175, and 200°C, respectively. At a room temperature, 10nm particles were partially superparamagnetic. The Mossbauer spectrum for the 7nm samples at room temperature displays superparamagnetic behavior as demonstrated by the single quadrupole doublet with zero hyperfine fields. Superparamagnetic particles display no sextet in Mossbauer spectra at temperatures above blocking temperature (TB=165K for the 7nm sample).

Effect of ferrite thermoseeds on destruction of carcinoma cells under alternating magnetic field

High iron-containing silicate glasses were prepared using a conventional melting and quenching process, and ferrimagnetic crystallites were precipitated via a nucleation and crystal growth mechanism. This study attempted to use these ferrite-containing glass-ceramics as thermoseeds for a hyperthermic cancer treatment under an alternating magnetic field. KB and L929 cells were used in the cell lysis experiments, as carcinoma and normal cells, respectively. These cells were mixed with an agar medium and stained prior to the annihilation test. After exposing the cells to the alternative magnetic field for 9 min, the number of carcinoma cells in the vicinity of the ferromagnetic specimen decreased with increasing time and almost all cancer cells were dead after 9 min while they were still alive in a region of 5 cm away from the specimen. When Sprague-Dawley rats imbedded the samples were exposed to a magnetic field, tumor cells disappeared after only 4 treatments of 15 min each. This amazing reduction in the tumor was not observed in any rats without the imbedded sample. It is expected that the prepared ferrite-containing glass-ceramics will be helpful in hyperthermic cancer treatment. Long-term research is needed to confirm this result.

The Effect of Manganese Substituted M-type Hexagonal Ba-ferrite

The Mn-substituted M-type Ba-ferrite (BaFe 12-x MnO 19 ; x = 0, 2, 4, 6) powders were prepared by the HTTD (High Temperature Thermal Decomposition) method. The effect of Mn 3+ Jahn-Teller ions on the magnetic properties has been studied by x-ray diffraction, vibrating sample magnetometry, and Mossbauer spectroscopy. With increasing Mn substitution, the lattice parameter a0 increases while c0 decreases. The magnetocrystalline anisotropy constants (K₁) were determined as 2.9, 2.2, 1.8, and, 1.3×10? erg/㎤ for x = 0, 2, 4, and 6, respectively, by the LAS method. We have studied the change of cation distribution by Mossbauer spectroscopy which is closely related to K₁.

Spin rotation at compensation point studies of Tb/sub 3/Fe/sub 5/O/sub 12/ by Mo/spl uml/ssbauer spectroscopy

The crystallographic and magnetic properties of Tb/sub 3/Fe/sub 5/O/sub 12/ were studied using X-ray diffraction, vibrating sample magnetometer (VSM), and Mo/spl uml/ssbauer spectroscopy. The crystal structure were found to have a single phase of garnet cubic structure, and the lattice constants of TbIG was found to be a/sub 0/=12.4364 /spl Aring/. The Rietveld refinement of X-ray pattern convinced that Tb ions fully occupied into the 24c site. The VSM measurements were performed in the temperature range from 30 to 700 K, which covers both the Ne/spl acute/el temperature (T/sub N/ = 560 /spl plusmn/ 5 K) and the compensation temperature (T/sub comp/ = 260 /spl plusmn/ 5 K). In order to elucidate magnetization on this sample, Mo/spl uml/ssbauer spectra of TbIG were measured at various absorber temperatures from 13 K to Ne/spl acute/el temperature. Over the compensation temperature, the Mo/spl uml/ssbauer spectrum for the sample was considered as a superposition of two sextets. However, below the compensation temperature, the spectrum of the sample showed an additional sharp sextet. Also, the additional set of spectrum persisted up to 260 K, and then disappeared above this temperature. This type of three iron sets in garnet system cannot be explained only by collinear magnetic moment or spin frustration. We suggest that this anomaly originates from the exchange interaction between the octahedral iron moment and the non collinear Tb moments. Temperature dependence of Mo/spl uml/ssbauer spectra at compensation point is closely related to noncollinear spin rotation.