Nanokette as a super magnet

Physicists succeed in the targeted Umpolung a chain of three iron atoms

Chain of three iron atoms © Yan et al. / Nature
Read out

The strongest permanent magnet in the world - as small as an atom: this record-breaking combination was created by a German research team with a sophisticated nano-experiment. They created a chain of three iron atoms whose magnetic field can be reversed with a microscope tip. This control option could spur the development of the quantum computer and open up alternative concepts for future storage media, as the researchers report in the journal "Nature Nanotechnology".

Atomic magnets are considered the storage media of the future and a possible basic unit for a quantum computer. Researchers have been experimenting for a long time with individual atoms or groups of atoms whose spin can be read as zero or one. Shichao Yan from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg and his colleagues have now developed a method with which an atomic magnet consisting of three iron atoms can be specifically reversed and controlled.

Nanokette reversed

For their experiment, the physicists first created the nanomagnet: On a smooth copper surface, they combined three iron atoms into a short chain with the fine tip of a scanning tunneling microscope. Next, they picked up more iron with their microscope - with the effect that a few iron atoms stuck to the tip, thereby making them magnetic. Then the researchers maneuvered the tip very tightly and with high precision over the iron chain.

Because the microscope can measure extremely fast processes, the team was able to analyze what happened within nanoseconds in the iron chain. The surprising result: "Depending on the position of the microscope tip, we were able to temporarily reverse the magnetic field of the iron chain, " says senior author Sebastian Loth of the MPI for the structure and dynamics of matter. "We were amazed how well that works."

Shichao Yan with a STEM image of the chain of 3 iron atoms. © MPSD / JM Harms

Stronger than any permanent magnet

The explanation: Due to a quantum effect, a magnetic field with special properties builds up between the microscope tip and the iron chain. "On the one hand, it is extremely strong, on the other hand it is very limited, " Yan reports. The strength reaches a value of several Tesla, more than the best permanent magnet. display

The extent of the field is limited to the range of an atomic diameter. This spatial limitation allows us to target the tiniest nanostructures, "explains Loth. A single atomic nucleus can be reversed, but its neighborhood is completely unaffected.

Usable for quantum computer and memory

This makes the new effect interesting for two applications. For example, it could be used as a control process for quantum bits - the switching unit of a quantum computer. "The new effect could make progress, " says Loth. With his help, one could selectively control individual magnetic quantum bits. The triatomic iron chain already shows some properties of a quantum bit. Now the researchers are thinking about how these properties can be further developed.

But even for data storage, the phenomenon could be relevant. Because the more magnetic bits you can write and read per area, the higher the storage capacity of a medium. "With our process, extremely small nanostructures can be magnetically driven, " says Yan. "In theory, it would be possible to increase the storage density by a few orders of magnitude."

However, the triatomic iron chains that the researchers have been experimenting with would not be useful: they can be efficiently reversed, but they lose their information within microseconds. Therefore, the researchers now want to apply the new effect to nanostructures that have what it takes to have stable magnetic bits. (Nature Nanotechnology, 2014; doi: 10.1038 / nnano.2014.281)

(Max Planck Institute for the Structure and Dynamics of Matter, 16.12.2014 - NP)