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Fully epitaxial Co 2 Fe x Mn 1Àx Si(CFMS)/Ag/Co 2 Fe x Mn 1Àx Si current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses t CFMS were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x ¼ 0.4 and t CFMS ¼ 3 nm. Enhancement of interface spinasymmetry was suggested for x ¼ 0.4 compared with that at x ¼ 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives. V

The Ni nanoparticles with fcc or hcp phases have been synthesized in tetraethylene glycol by using the modified polyol process. The crystal structure has been controlled by changing the polyol/Ni mole ratio and the reaction temperature. The saturation magnetization of the as-prepared particles depends on the relative volume fraction of the hcp phase. The x-ray diffraction and extended x-ray absorption fine structure studies suggest the formation of pure fcc and hcp Ni phases. The hcp Ni particles show nonmagnetic behavior and thermally stable below 673K.

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Chemically ordered hard magnetic L10-FeNi phase of higher grade than cosmic meteorites is produced artificially. Present alloy design shortens the formation time from hundreds of millions of years for natural meteorites to less than 300 hours. Electron diffraction detects four-fold 110 superlattice reflections and a high chemical order parameter (S  0.8) for the developed L10-FeNi phase. The magnetic field of more than 3.5 kOe is required for the switching of magnetization. Experimental results along with computer simulation suggest that the ordered phase is formed due to three factors related to the amorphous state: high diffusion rates of the constituent elements at lower temperatures when crystallizing, a large driving force for precipitation of the L10 phase, and the possible presence of L10 clusters. Present results can resolve mineral exhaustion issues in the development of next-generation hard magnetic materials because the alloys are free from rare-earth elements, and the technique is well suited for mass production.

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Microcrystals of coesite and stishovite were discovered as inclusions in amorphous silica grains in shocked melt pockets of a lunar meteorite Asuka-881757 by micro-Raman spectrometry, scanning electron microscopy, electron back-scatter diffraction, and transmission electron microscopy. These high-pressure polymorphs of SiO 2 in amorphous silica indicate that the meteorite experienced an equilibrium shock-pressure of at least 8-30 GPa. Secondary quartz grains are also observed in separate amorphous silica grains in the meteorite. The estimated age reported by the 39 Ar∕ 40 Ar chronology indicates that the source basalt of this meteorite was impacted at 3,800 Ma ago, time of lunar cataclysm; i.e., the heavy bombardment in the lunar surface. Observation of coesite and stishovite formed in the lunar breccias suggests that highpressure impact metamorphism and formation of high-pressure minerals are common phenomena in brecciated lunar surface altered by the heavy meteoritic bombardment.he lunar meteorites are unique samples, which provide information on the unexplored surface of the moon. The high-pressure polymorphs usually reported in impact craters of the Earth's surface have not been reported in lunar samples, and differences in impact conditions in the lunar surface have been suggested by previous workers; i.e., absence of high-pressure polymorphs of silica might be caused by volatilization during impact events in the high vacuum at the lunar surface (e.g., refs. 1 and 2). However, this is an unrealistic interpretation because volatilization during impact would require temperatures exceeding 1,700°C. In addition, such volatilization would induce fractional sublimation of volatile elements like Na and K, for example, and much more importantly, isotopic mass-dependent fractionation of oxygen and magnesium. These features were never observed in shocked lunar samples. The lunar meteorites contain information on the shock events that were common in the early lunar surface. Asuka-881757 lunar meteorite was discovered in Antarctica, and was described by some authors (3, 4). This lunar meteorite is composed mainly of coarse aggregates of pyroxene, plagioclase (maskelynite), and ilmenite. It shows a variety of shock features such as the existence of maskelynite and glass matrix with compositions of mixtures of pyroxene and plagioclase that is clear evidence for melting of both plagioclase and pyroxene by shock and quenching of the melt mixture.The difference in the age determined by 147 Sm-143 Nd and 39 Ar∕ 40 Ar chronologies (5) indicates that the source basalt of this meteorite crystallized at 3,870 Ma and was impacted at 3,800 Ma, which is the time of the heavy bombardment on lunar surfaces. Therefore, the shock features recorded in this meteorite might provide information on conditions during the heavy meteoritic bombardment in the Moon. The cosmic-ray exposure age of this meteorite is one million years (6), which suggests that the meteorite was exposed in the space perhaps after launching from the lunar surface one ...

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