Magnetic skyrmions are chiral spin structures with a whirling configuration, considered as units (bits) in new magnetic data storage devices. Despite they were predicted in the 80's, they were not evidenced till 2006. However, they could only be seen under very special conditions (at very low temperatures, applying magnetic fields, in bulk samples or films grown by molecular epitaxy). These constraints made impossible their application in industrial devices. Skyrmions nanostructures are named after British physicist Tony Hilton Royle Skyrme.
Now, a group of researchers led by Olivier Boulle from SPINTEC (Grenoble, France) has reported the first observation of magnetic skyrmions under conditions more appropriate to the industrial needs: room temperature, zero magnetic field and sputtered ultrathin films.
The researchers stabilized and imaged skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures. The sputter method offers fast, large scale, high reproducibility deposition and is the standard of semiconductor and microelectronics industry.
Samples were analysed at the CIRCE beamline of the ALBA Synchrotron, using the Photoemission Electron Microscope (PEEM) with X-Ray magnetic circular dichroism (XMCD) magnetic contrast, and a similar microscope in Elettra. Using these techniques, they could solve the skyrmion spin structure. In addition, researchers were also able to study skyrmions behaviour under small applied magnetic field at the ALBA Synchrotron, demonstrating their stability against perturbations.
"These results constitute a crucial step for the integration of skyrmions into information storage and processing devices in the future", according to Olivier Boulle
The next goal of the research is to image the movement of such skyrmions by small electrical currents which would allow their manipulation at the nanoscale in memory devices.
Magnetic skyrmions, key for the development of new data storage and processing systems
As skyrmions are very small (nanometer size), they are very appropriate for creating high-density information devices. The separation between bits can be much smaller than with other structures, avoiding any inference between the magnetic fields.
Skyrmions can also be moved by very small electrical currents. This means that devices with skyrmions will need much less power than up-to-date systems.
Another characteristic of skyrmions is their stability, making difficult their destruction and, thus, keeping information for longer times.
Fig. 1: Sketch of the spin structure of a magnetic skyrmion.
Fig. 2: (a) Magnetic microscopy image of a skyrmion in a Pt/Co/MgO nanostructure. Within the white dot (magnetization pointing down), a circular black/white contrast is visible which corresponds to the in-plane magnetisation components. In the skyrmion center, dark grey, the magnetization points up. The grazing X-ray beam incidence is indicated by the arrow (b). The skyrmion contracts under an applied magnetic field of 4mT and relaxes again when removing it (c). (d) The chiral skyrmion spin structure is confirmed by rotating the contrast direction (beam incidence) by 90°.
