Nanostructure Science and Technology - World Technology ...

Appendix D. Site Reports—Japan 293
sputtering that contains Hf, Ta, C, which on crystallization gives 10 nm Fe
particles whose grain boundaries are pinned by about 10 nm diameter
carbide (e.g., Fe 80 Hf 8 C 12 ) particles, which stabilize the nm grain size up to
elevated temperatures (~ 700°C). This material exhibits almost constant
permeability µ', with frequency up to about 10 MHz while the µ"
(imaginary, lossy) component rises at values between 1 and 10 MHz.
Another interesting topic involves preparation and property
measurements of metal/nonmetal granular nc composites. Sputtering was
used to form systems such as Fe/SiO 2 , Co/Al 2 O 3 . As the oxygen
concentration in the films increases, the electrical resistivity increases from
metallic (10 1 –10 2 µΩcm), to a ρ vs. T behavior with a ρ minimum with
ρ = 10 2 –10 3 µΩcm, to high resistivity (negative coefficient of ρ) with
ρ = 10 4 –10 10 µΩcm. The low oxygen content composites show
ferromagnetic behavior with high permeabilities—about double that of
ferrites but with higher losses. A potential application is use as a high
frequency inductor.
The oxygen-rich composites exhibit giant magnetoresistance (GMR). For
example, the Co, Fe in Al 2 O 3 provides an assembly of tiny tunneling
junctions with ∆ρ/ρ o about 7.8%.
Fujimori’s magnetic materials program is expected to receive an
additional $3.8 million in government funding for the next five years in a
new program entitled, “Nanostructurally controlled spin dependent quantum
effects and new electronics and magnetics.” A goal is a one-electron spin
memory.
Prof. A. Inoue (Carl Koch)
Professor Inoue’s large group (41 persons) studies amorphous, quasicrystalline,
and nc materials. The nc materials are typically prepared by
crystallization of amorphous precursors, which can be bulk amorphous
alloys, ribbons or wires produced by melt spinning, or rapidly quenched
powders produced by powder atomization methods. Mechanical tests on
nc/amorphous alloys from bulk amorphous samples exhibit increased yield
strengths but little elongation in tension—that is, behavior similar to
amorphous alloys even though 60–70 vol.% of the material is crystalline.
Mg-base alloys have been successfully studied in this regard.
The equipment for processing, material characterization, and property
measurements in Inoue’s laboratory is very impressive indeed, with most
nonequilibrium processing tools, sophisticated characterization, and property
measurement facilities available.
The innovative work on metastable materials Professor Inoue has carried
on over the years cannot be praised too highly. He and his coworkers are