Novel concepts of magnetic data storage aim to send very small magnetic bits back and forth in a memory chip, store them tightly packed and read them out later. The magnetic stray field previously prevented the production of very small bits. Now researchers at the Max Born Institute (MBI), the Massachusetts Institute of Technology (MIT) and DESY have succeeded in creating a “magic hat” for magnetic nanostructures. In this way, the stray magnetic field can be reduced so that the bits can be both small and very mobile at the same time. The research results appeared in “Nature Nanotechnology“.
For physicists, magnetism is fundamentally linked to rotational movements of electrons in atoms. The electrons, which revolve around an atomic nucleus and also revolve around themselves, generate the magnetic moment of the atom through this movement. It is the magnetic stray field associated with this magnetic moment that we all know from a bar magnet and use to attach notes to a magnetic pin board. Likewise, the stray magnetic field is used to read magnetically stored information from a hard disk. In today’s hard drives, a single magnetic bit is only about 15 x 45 nanometers, about 1,000,000,000 of them would fit on a stamp.
In novel concepts of magnetic data storage, one would like to send such magnetic bits back and forth by means of current pulses in a memory chip in order to store them in a suitable place packed for storage and to read them out again later. Here, the magnetic stray field now turns out to be a curse: it prevents the magnetic structures from being made smaller and information more tightly packed. On the other hand, the magnetic field underlying the stray field is needed to be able to move the structures at all.
The researchers have now been able to put a “magic cap” on small magnetic nanostructures and observe how small and fast such disguised bits can be. For this atom types were combined with opposite direction of rotation of the electrons and thus opposite magnetic moment. In this way, the magnetic stray field can be reduced or even completely switched off – but the individual atoms in the nanostructure still have a magnetic moment, they have only a cloak of invisibility.
Nevertheless, it was possible for the researchers to reproduce the small structures. They used the method of x-ray holography, which makes it possible to make only visible the magnetic moments of a single atomic species – so the structures could be imaged without their cloak of invisibility.
It showed that by skillfully adjusting the power of the cloak of invisibility two things can be achieved that are important for possible applications as data storage. “In our pictures we can see very small, round magnetic structures”, explains Dr. med. Bastian Pfau from the MBI. “The smallest diameters we found are only 10 nanometers”. If these structures could be used for data storage, the storage density could be significantly increased compared to today’s hard disks. In further measurements at MIT, the researchers also discovered that camouflaged nanomagnets can be moved very quickly by current pulses – an important property for a possible application. So speeds of over one kilometer per second were reached.
“That this is possible is a consequence of quantum physics,” explains Prof. Stefan Eisebitt from the MBI. “The contribution of the rotational movement of an electron around the atomic nucleus to the magnetic moment is only half as large as the contribution that the rotation of the electron makes to itself.” Combining different types of atoms with different directions of rotation of the electrons in a solid, then you can Total rotation – the physicists speak of the so-called angular momentum of the system – therefore extinguish and still maintain a small magnetic moment. Since the angular momentum leads to a deceleration of the movement of the magnetic structures by current pulses, high speeds can be achieved with this approach. So it succeeds to adjust the cloak exactly
Source : Forschungsverbund Berlin e. V.