A single-atom magnet with unprecedented levels of stability has been developed by Swiss researchers, heralding a major milestone in the ongoing miniaturisation of data storage devices.
The magnet is made of a chemical compound called holmium – a rare-earth element that can be naturally found in the minerals monazite and gadolinite.
The major difference between the holmium-based magnets and other atom-level magnets that scientists have experimented with previously is its remanence. Magnetic remanence is the ability of a magnet to remain magnetised, which decreases with the size of the magnet and is generally extremely limited at the atom level. Such small magnets are easily affected by the environment. Their magnetic field can be easily flipped, which limits the practical use in data storage devices.
However, the holmium magnet, described in an article in the latest issue of the journal Science, defies the rules due to its electron structure.
The team from Swiss universities ETH Zurich and École polytechnique fédérale de Lausanne (EPFL) created the holmium magnets by placing single holmium atoms on ultrathin films of magnesium oxide grown on a surface of silver.
In experiments, the magnets were stable at temperatures of around -233 °C, which, according to the scientists, is the highest temperature at which any atom-level magnet has ever been stable.
The holmium magnet is not only the most stable but also the smallest ever created, as previous atom-level magnets usually consisted of between three and 12 atoms.
The miniaturisation of digital technology puts pressure on developers of data storage devices, who need to reduce the size of the systems hand in hand with that of the chips.
Computer hard drives and memory cards store data in the form of magnetic information, which is defined by the spin of the electrons in the magnets. Electrons can spin up or down, creating a tiny magnetic field. In an atom, electrons usually come in pairs with opposite spins, thus cancelling out each other's magnetic field. In a magnet, atoms have unpaired electrons and their spins create an overall magnetic field.