Picometer‑sized magnets in free‑electron‑laser light

Atomic clusters represent an ideal model system to study size‑driven
effects in solids. Indeed, such clusters provide a self‑contained
`laboratory' where, as a function of the number of constituent atoms,
condensed matter effects gradually appear. Particularly intriguing is
the evolution of the geometric and electronic structure, and their role
in the appearance of magnetic ordering in increasing the size of the
system from a single atom to a macroscopic unit.

Knowing the structure of a cluster is thus the first important step in
understanding more complex properties. This is a challenging task since
none of the usual spectroscopy techniques work on low‑density gas‑phase
clusters. However, we prove it possible using intense tunable infrared
light from a free electron laser. The laser radiation was used to
resonantly shake a small messenger molecule off the cluster surface.
Thus obtained vibrational spectrum was proven to be a unique fingerprint
of not only the geometric, but also the magnetic configuration of the
clusters. For example, a tiny object with only four Fe atoms was shown
to be a ferrimagnet with a large exchange energy.


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LT12529

How to make water ‘bounce’ at the nanoscale

In our cells, water is stuck between molecules with only a few nanometers to spare. Such ‘nanoconfined’ water has long been suspected of having unique properties. Now a team of physicists at Wayne State University has measured the mechanical properties of water squeezed down to just a few molecules, and found that water can be switched from being a liquid to a bouncy solid by small changes in external conditions. Using a new Atomic Force Microscope technique developed at Wayne State, the team probed the mechanical properties of confined water layers without disturbing them. Oscillating a tiny probe, immersed in the liquid, with amplitudes the size of a hydrogen atom (0.1 nm), they recorded the response as the probe squeezed the water at extremely low speeds. Once squeezed to a layer four molecules thick or less, the water behaved like honey: more viscous than in bulk, but still liquid. However, at squeeze speeds of 0.8 nm/s and above, water became elastic. This speed is so slow, it would take 12 years to move one foot, yet it is enough to change the behavior of water drastically.