High temperature Néel skyrmions in simple ferromagnets

A wide variety of chiral non-collinear spin textures have been discovered and have unique properties that make them highly interesting for technological applications. However, many of these are found in complex materials and only in a narrow window of temperature. Here, we show the formation of Néel-type skyrmions in thin layers of simple ferromagnetic alloys, namely Co-Al and Co-Ni-Al, over a wide range of temperature up to ~773 K, by imposing a strain gradient perpendicular to the sample plane via epitaxy with an Ir-Al underlayer. The Néel skyrmions are directly observed using Lorentz transmission electron microscopy in freestanding membranes at high temperatures and the strain gradient is directly measured from x-ray diffraction asymmetric peak profiles. Our concept allows for simple centrosymmetric ferromagnets with high magnetic ordering temperatures to exhibit skyrmions at temperatures well above room temperature, thereby, bringing closer skyrmionic electronics. Skyrmions are usually restricted to complex materials and within these, only exist for a narrow temperature range. Here, Wang and coauthors demonstrate the formation of skyrmions in layers of Co-Al and Co-Ni-Al alloy grown with a strain gradient, stable from room temperature up to 773 K.