A team of researchers from EPFL have constructed a single-atom magnet that possesses the highest stability to-date. The innovation will enable the scalable production of miniature magnetic storage devices.
Memory cards and computer hard drives are examples of the magnetic storage devices that are currently available. However computer technology is growing smaller, which requires the miniaturization of data storage. Researchers are striving to build magnets that are the size of a single atom. The key issue with atom-sized magnets is that it will be tough to keep "magnetized", which means it would be unable to retain data for a meaningful amount of time.
The EPFL team have successfully constructed an atom-sized magnet. Their findings have been published in the Science journal. It operates at about 40 K (-233.15°C), and it is the world’s smallest and most stable magnet currently. Magnets operate due to the electron spin, which is similar to a spinning top. The electrons spin in an up and down direction, creating a miniature magnetic field. Electrons are usually found in pairs in an atom and possess opposite spins, which help to cancel the magnetic field of each other. In magnets the atoms possess unpaired electrons, and their spinning produces a magnetic field.
Constructing smaller and smaller magnets to use in data storage devices is a challenge today. The issue is termed "magnetic remanence", which refers to the magnet’s ability to retain its magnetic capacity. Remanence is often difficult to observe in a single atom as the environmental fluctuations tend to flip its magnetic field. Under the technology umbrella, this would mean limited remanence, which would translate as limited data storage for atom-sized magnets.
The EPFL team, with colleagues at ETH Zurich, was headed by Harald Brune. Together they constructed the prototypical miniature magnet using atoms of the rare-earth element holmium. On ultrathin films of magnesium oxide, the team placed single holmium atoms. The films were grown on a silver surface. This technique facilitates the arrangement of single-atom magnets with strong remanence. This is possible as the electron structure of holmium atoms prevents the flipping of the magnetic field.
At about 40 K (-233.15°C), the holmium atoms’ magnetic remanence is stable, and this is by far the highest achieved. Based on scientific calculations, the remanence is much higher than those seen in existing magnets made up of 3-12 atoms. This novel single-atom magnet has broken a worldwide record in stability as well as in size.