Synopsis: When magnetism unchains a break junction

First-principles calculations explore how magnetic interactions impede the formation of atomically thin wires.

A monatomic chain of atoms left suspended across the tips of a broken wire (a break junction) is potentially a model one-dimensional system. These atomically thin wires are important in the study of fundamental magnetism and could eventually play a role in technological applications in spintronics and quantum computing. There are, for example, theoretical predictions that chains of magnetic transition metal atoms will be more magnetic than their bulk forms.

Although it has been possible to make long monatomic chains of selected nonmagnetic transition-metal elements and magnetic transition-metal chains on a surface, creating suspended chains of magnetic transition metals across a break junction has proven difficult. To find out why, Alexander Thiess, Yuriy Mokrousov, and Stefan Blügel at Forschungszentrum Jülich and Stefan Heinze at Christian-Albrechts-Universität zu Kiel, both in Germany, report in Physical Review Letters first-principles calculations on the process of how a monatomic chain forms from a break junction. They show that the presence of a local magnetic moment suppresses chain formation in $3d$, $4d$, and $5d$ elements because it effectively lowers the hardness of the chain. This explains why gold, silver, iridium, and platinum—all nonmagnetic elements in bulk—can form long chains and why similar efforts to make iron strands only yielded shorter nanocontacts. – Daniel Ucko

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