Observation of new-type magnetic skymrions with extremerely high temperature stability and fabrication of skyrmion-based race-track memory device

Nanoscle magnetic skyrmions are topologically protected vortex-like spin textures that have been regarded as a promising candidate for the transport of information in further spintronic applications based on the racetrack memory concept due to their nanoscale dimension, stable particle-like feature, and an ultralow threshold for current-driven motion. Recently, most of the skyrmions are observed in chiral magnetic materials, such as MnSi, FeGe, Co-Mn-Zn, where the Dzyaloshinskii-Moriya interaction is active. However, their overall low thermal stability is one of the major factors hindering the practical applications. In this paper, we report the observation of a new-type magnetic skyrmion with extremerely high temperature stability in the centrosymmetric frustrated magnet Fe3Sn2, and the fabrication of skyrmion-based race-track memory device based on Fe3Sn2 by using focused ion beam. This compound is a rare example of ferromagnetic frustrated magnet that exhibits a high Curie temperature Tc up to 640 K. As the temperature decreases from 640 K to 100 K, it undergoes a spin reorientation during which the easy axis rotates gradually from the c-axis to the ab-plane. The Fe3Sn2 has a layered rhombohedral structure with the alternate stacking of the Sn layer and the Fe-Sn bilayer along the c-axis. By a high-temperature flux method, we grow high-quality Fe3Sn2 single crystal. The in-situ Lorentz transmission electron microscopy (LTEM) observations demonstrate that this compound can host skyrmions at room temperature (RT). In contrast to the skyrmions of the chiral magnets, they possess various spin textures and are transformed from topologically trivial bubbles under a high external magnetic field of 800 mT. By using the FIB technique, we fabricate a geometrically confined nanostripe with a width of 600 nm and thickness of 250 nm. The in-situ LTEM observations demonstrate that a single chain of skyrmions with uniform spin textures can be created at RT. The investigations on the temperature stability of the single skyrmion chain reveal that it shows an extremerely high temperature stability that the size of and the distance between the skyrmions in the chain can keep unchanged at temperatures varying from RT up to a record-high temperature of 630 K. The observation of a highly stable single skyrmion chain in the geometrically confined Fe3Sn2 nanostripe can be attributed to (1) the weak temperaturedependent magnetic anisotropy Ku of the Fe3Sn2 crystal, and (2) the formation of edge states at the boundaries of the nanostripes. The observation of new-type magnetic skymrion with extremerely high temperature stability and the fabrication of skyrmion-based race-track memory devices are very important steps towards the applications in skyrmionbased spintronic devices.