14th Magnetic Materials Center Seminar
April 20, 2006, 9:00am
7th floor seminar room, Sengen
Making of High Density and Monodispersed Magnetite Nanoparticles
Hayato Takeshita
The magnetic moment of a small ferromagnetic particle changes with thermal energy, as the size of single domain particle reduces to few nm it becomes super-paramagnetic. When the temperature is reduced, thermal energy becomes smaller than the magnetic anisotropic energy , and the magnetic moment is fixed. My research was to make uniform volume distribution, high density bulk magnetite nano particles. Ferrofluid in colloidal solution form has been used to make nano particle magnetite. In the present work we tried to reduce the particle size by adding polymer when magnetite is made, to achieve high density. The densities increased by three times more than ferrofluid as measured with a VSM. However, the particle size did not change, but distance between the particles reduced and the density is increased. It is necessary to do the TEM sudies for observing the particle arrangement and size distribution.

Irradiation effects by gold cluster ions in silicon single crystal
Tomoya NAKATANI
I was belong to Osaka Prefecture University, college of engineering, faculty of material science until last month, and had studied irradiation effects by cluster ions in solid. Today, I will introduce an abstract of my bachelor thesis. Cluster ions might have different irradiation effects from those by individual atoms when the total number of the atoms and velocity are the same, that is, for example, effects by 3 MeV cluster ion composed of three atoms are different from those by three 1 MeV mono-atomic ions. Let name this phenomenon “cluster effect”. Up to now, cluster effects were found with spectroscopy of secondary electron or secondary ion and Ratherford back-scattering spectroscopy, mainly in atom and molecular physics. In this study, pre-thinned silicon wafers of 111 orientation were irradiated with 1.66 MeV/atom gold mono-atomic and cluster ions, Au+, Au2 +, Au3 + at room temperature. These samples were observed with TEM using by conventional techniques (bright field, dark field weak-beam method and selected electron diffraction). At low fluence (1x1012 Au/cm2, corresponding to 0.48 dpa), it was cleared that the yield and size distribution of defects produced by irradiation damage increased with increasing cluster size, which is the number of atoms composing of cluster. At high fluence (6x1012 Au/cm2), all of specimens irradiated with Au+, Au2 + and Au3 + respectively, were amorphized, however, at the lower fluence, amorphization was observed for only samples irradiated with cluster ions. In these points, we observed the cluster effect.

Molecular Weight Dependence of Over-all Crystallization rates for Poly(ethylene succinate)
Yimeng Chen , Kayo NAKAMURA, Susumu UMEMOTO and Norimasa OKUI
Abstract: The molecular weight(Mw)dependence plays an important role of the crystallization of polymers however, the detail discussion for Mw dependence of over-all crystallization rate has not been sufficient. Several theoretical considerations such as Avrami equation which are not based on the actual nucleation behavior have been widely used. In this study, we derivate the new theoretical equation, and discuss the Mw dependence of over-all crystallization behavior. The over-all crystallization behaviors for 10 samples with different Mw were measured by the transmitted light intensity. The typical relative crystallinity: X and nucleation behavior were shown in Fig.1. The nucleation saturated in the early stage and could be expressed well by Eq.２, whereas the X increased with increasing of the time. Eq.１ for over-all crystallization behavior with 2-dimmensional spherulite growth could be induced on the basis of Eq.1, and ln(1-X) was plotted against the values in Eq.１ as shown in Fig.2. The linear relations were obtained, therefore, the actual behavior could be expressed by Eq.１ The Mw dependence of the slopes in Fig.2 as the indexes of over-all crystallization rate: k can be expressed as k∝IaG2 where I: nucleation rate, G: growth rate and a=0.4.The Mw dependence of the over-all crystallization rate can be also expressed as the power law.