31st Magnetic Materials Center Seminar
November 27, 2006, 10:30
7th floor seminar room, Sengen
Nanostructured Materials for Magneto-Optical Applications
B. Varaprasad
Transparent crack-free and bubble free Fe3+ doped silica gel-glasses were prepared via sol-gel route for magneto optical applications. Homogeneous dispersion of iron oxide nanoparticles in an inorganic matrix is also one of the current interests for the production of new composite with controlled structures, morphologies and of unique properties. We have been interested in fabrication of composite materials by in situ generation of iron oxide nanoparticles in silica matrix through sol gel process. The process involves the hydrolysis and condensation of 1:3:10:X (1≦ X ≦ 20) molar ratios of tetraethoxysilane, absolute ethanol, aqueous nitric acid (0.016 N)and ferric nitrate respectively, and subsequent thermal treatment at temperatures ranging from 1100C to 10000C. The composite materials obtained at different iron concentration and suitable thermal treatments and the methods employed in structural and magnetic characterization are X ray diffraction, Fourier transform infrared spectroscopy, termogravimetry, Transmission electron microscopy and Vibrating sample magnetometer. The XRD results of higher molar ratio show that the obtained materials have γ-Fe2O3 and α-Fe2O3 phases depending on the thermal treatment conditions. It has observed that the presence of magnetic component (Fe2O3) in silica matrix modified the gel morphology leading to strong structural and chemical changes. Iron oxide nanoparticles of different sizes (10-100 nm) were obtained in silica matrix depending on the iron concentration and thermal treatment which influence structural and magnetic properties to a large extent. The information about the structural variation of the gel-glasses and their influence on physical properties during annealing has been studied. It has been observed that monolithicity and chemical environment around Fe3+ of the gel-glasses are strongly dependent on the molar ratio of the starting materials, annealing temperature ageing time and ageing conditions. Colour of gel-glass samples is different for different annealing temperatures. This is mainly due to the different co-ordination state of Fe3+ and generation of Fe2O3 colloid. The high optical quality of Fe3+ doped silica gel-glasses facilitate tuning of UV-visible absorption cut-off edge via annealing process and exhibits marked differences in their magnetic properties with annealing temperature. Magneto optical studies were performed on gel glasses doped with 1 mole % Fe3+ at various annealing temperatures. Higher mole % Fe3+ Doped gel glasses are become opaque for visible light because of the iron oxide colour but having interesting magnetic properties.

Shear bands and plasticity of BMGs
G. Kumar
The extent of plastic deformation in BMGs is predominantly dependent on the number and type of shear bands generated, which varies as a function of alloy composition and preparation conditions. BMGs based on Zr-Cu system received a significant attention because of their large compressive plastic strain and an unsettled issue of "strain hardening". The clear understanding of mechanical behavior of Zr-Cu based BMGs lingers because these BMGs are particularly prone to surface artifacts generated by thinning techniques like electropolishing or ion milling or even by electron beam during TEM observation. The aim of this study is to unambiguously characterize Zr-Cu-Al BMGs that show a markedly different strain values despite a small variation in the compositions. Different views in literature along with present results will be discussed. Additionally, TEM results of shear band observation in some metallic glasses will be presented.

Application of energy filtered TEM
T. Ohkubo
Energy filtered TEM is very useful techniques which can get many information from nanoscale region. There are two types of energy filtering system. One is 'In-column type', other is 'Post-column type'. We can use both types in NIMS. Therefore, it is very important to understand the feature and the application. In this talk, I would like to explain the basis and application of these techniques such as elemental/thickness mapping or radial distribution function analysis.