Researchers take step towards smaller storage media with nanodisks

German and French researchers have found a way to store information in magnetic vortices on nanodisks and to read them reliably. The team claims that using this principle allows more data to fit on smaller storage media.

The method works by detecting the direction of the magnetic vortex in the nanodisks. Nanodisks are very small and thin disks of ferromagnetic material. In nanodisks, spin is responsible for forming magnetic vortices. The spins, which determine the magnetic moment of the electrons, are arranged as if ordinary bar magnets are arranged in a row behind each other in a circle.

In the center of the nanodisk, however, the magnetic field lines are perpendicular to the plane of the disk. These two properties, the circulation of the magnetism in the disk plane and the magnetic orientation of the core, ensure the storage of information. In this way, two bits of information can be stored with a single vortex. Two vortices on top of each other can already store four bits and correspond to sixteen different states.

The type of magnetic nanopillar with two superimposed vortices described by the scientists in Nature Communications is only 50 nanometers high and 150 nanometers in diameter. Influencing the direction of the vortex and the magnetic direction of the core was not much of a problem, the biggest obstacle was reading the information from the disks. One of the researchers, Attila Kákay, explains that the polarity of the core was difficult to read because it was simply too small.

The solution to still be able to read the small magnetic force was to use microwaves. The alternating electrical signals are emitted by the stacked vortices when they are connected to direct current. The frequencies of the microwaves are used to determine the polarity of the core and to measure the direction of rotation of the vortices.

On the HZDR news site, Kákay explains it using a flute: “The principle is similar to that of a flute where each finger position over the holes of the flute sounds a different note, or a different frequency.”