How “lasagne” become “Bolognese”:
x-ray spectra reveal how magnetic phases mix together in magnetoresistive
artificial layered structures
Manganites, a class of materials based on manganese and oxygen, are famous
for magnetoresistance, i.e. for changing resistivity under external
magnetic fields. However manganites of simplest composition, such as
LaMnO3 or SrMnO3, are insulating and antiferromagnetic; and only at
intermediate chemical composition, e.g. (LaSr)MnO3, they become
conductive, ferromagnetic and magnetoresistive. At atomic scale
magnetoresistive manganites are chemically disordered and appear as
“Bolognese” spaghetti, a random mixture of pasta and meat sauce, i.e. of
LaMnO3 and SrMnO3. Recently it was shown that magnetoresistance can be
obtained also in artificial layered structures, where LaMnO3 and SrMnO3
are alternated similarly to pasta and meat in “lasagne”. Indeed the trick
works only if the layers are thin enough. Using synchrotron radiation for
measuring x-ray absorption spectra, we have directly seen, at atomic
scale, how LaMnO3/SrMnO3 superlattices become similar to (LaSr)MnO3, i.e.
how it happens that “lasagne” can taste as “Bolognese”. Our measurements
provide a detailed description of the distribution of antiferromagnetic
and ferromagnetic regions across the material, providing useful
information on how to possibly improve the manganite recipe. A high
density of interfaces is the “secret ingredient”: the more of them you
have the better your “lasagne” will taste.
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LD12763
Shortest light flashes ever from ultra-hot state of matter
Recent calculations show that the quark gluon plasma, a state of matter
created in heavy ion collisions at the particle accelerator RHIC and soon at
the LHC, emits light with pulse duration a million times shorter than present-
day ultra-fast lasers. Researchers strive for ever shorter and more energetic
light pulses, as these allow for measurements with better resolution in space
and time. Quark gluon plasmas are intensely studied as they are thought to
resemble the state of our universe at its very beginning. In this work, we
show that their remarkable properties advance the presently available light
sources to durations in the yoctosecond range (a number with 24 zeros in front
of the first non-zero digit), and to photon energies in the high-energy range.
This could open up the time-resolved study, e.g., of nuclear processes.
Remarkably, under certain conditions, controlled double light flashes could be
emitted. Such double flashes might eventually lead to the creation of the first
slow-motion movie ever of nuclear dynamics.
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LE12337
Bacteria Thin Liquids
Common swimming bacteria such as Bacillus Subtilis
dramatically reduce the viscosity of liquid they swim in. A seven-fold
viscosity reduction was observed in two independent experiments with the
suspensions of bacteria confined in thin soap-like fluid films. The
scientists also discovered that the viscosity depends on the
concentration and the swimming speed of bacteria. The primary mechanism
of the viscosity reduction is related to transformation by bacteria of
chemical energy of the nutrient into kinetic energy of fluid motion.
The study sheds a new light on physical properties of a variety
biological fluids. In addition, the results are important for
fundamental and technological reasons, from understanding collective
motion in groups of interacting animals such as bird flocks and fish
schools to miniature bacteria-powered mixers and reactors.
Image:
schematics of "bacterial viscosimeter". Tiny movable probe creates a
vortex in thin soap-like film, the viscosity is extracted from the
vortex decay time.
