These nanoscale magnetic structures have been observed at room temperature in materials compatible with industrial conditions. This breaks an important barrier for their use as nanoscale information carriers in our computers. Results - obtained at the CIRCE beamline - have been published in Nature Nanotechnology.

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.

Fig. 1: Sketch of the spin structure of a magnetic skyrmion.

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. 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°. 

Reference: Olivier Boulle, Jan Vogel, Hongxin Yang, Stefania Pizzini, Dayane de Souza Chaves, Andrea Locatelli, Tevfik Onur Menteş, Alessandro Sala, Liliana D. Buda-Prejbeanu, Olivier Klein, Mohamed Belmeguenai, Yves Roussigné, Andrey Stashkevich, Salim Mourad Chérif, Lucia Aballe, Michael Foerster, Mairbek Chshiev, Stéphane Auffret, Ioan Mihai Miron & Gilles Gaudin.  "Room temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures" Nature Nanotechnology (2016). doi: 10.1038/nnano.2015.315