65th Magnetic Materials Center Seminar
December 14, 2007, 9:00-
8th floor middle seminar room, Sengen
Epitaxial growth of Co2FeAl0.5Si0.4 thin films on MgO-buffered MgO (001) substrates and their their tunnel magnetoresistance characteristics
W. H. Wang
In this presentation, I will show you our recent studies in terms of the optimization of L21-Co2FeAl0.5Si0.4 (CFAS) epitaxial thin films on MgO-buffered MgO (001) substrates using magnetron sputtering and in situ annealing parameters. According to these optimized parameters, we have successful fabricated a fully epitaxial spin-valve-type CFAS/MgO/CFAS magnetic tunneling junction (MTJ), and a large TMR ratio up to 130% at RT has been achieved.

Microstructure evolution of two phase materials processed by accumulative roll bonding
K. Oishi
Severe plastic deformation (SPD) has been known as a technique to provide ultrafine grained and nano-grained structure. When the SPD is applied to two phase alloys, the dissolution of precipitates and the formation of supersaturated solid solution occur. In our group microstructure characterization has been done on multilayered stacked materials of Cu-Ag and Cu-Zr processed by accumulative roll bonding (ARB). This study showed that a supersaturated solid solution forms in the Cu-Ag material, while amorphization occurs in the fine Zr layer in the Cu-Zr material. In preset work microstructural variations of multilayered Cu-Ni material subjected to ARB were investigated using TEM. At the beginning of deformation, banded structure was observed in both Cu and Ni layers. The size of elongated grain in Ni layers was smaller than that of Cu ones. By further ARB process the layered structure along the rolling direction evolved and became finer for both phases. At the ARB process of 8 cycles the layer spacing reached about 20 nm and a solid solution formed partially.

Spin injection switching
K. Inomata
Low current spin switching is a critical issue as well as anti-thermal spin fluctuation problem in magnetic nano-devices. First I will give an introduction for spin switching by an external filed for single-layer and antiferromagnetically coupled nano-magnets. Next, I will explain the spin injection switching and talk how the current density can be reduced for spin injection switching.