Skyrmions in synthetic antiferromagnets and their nucleation using electrical current and ultrafast laser illumination

Magnetic skyrmions are topological spin textures which hold great promise as nanometer scale information carriers in memory and logic devices. While room temperature magnetic skyrmions and their current induced manipulation were recently demonstrated [1–5], the stray field resulting from their magnetic moment as well as their topological charge limit their minimal size and reliable motion in tracks. Antiferromagnetic (AF) skyrmions allow to lift these limitations owing to their vanishing magnetic moment and canceled topological charge, promising room temperature ultrasmall skyrmions, fast dynamics and insensitivity to external magnetic fields. While room temperature AF spin textures have been recently demonstrated [6–9], the observation and controlled nucleation of AF skyrmions operable at room temperature in industry compatible AF material systems is still lacking. Here we demonstrate that isolated skyrmions can be stabilized at zero field and room temperature in a fully compensated SAF. SAF based on (Pt/Co/Ru/Pt/Co/NiFe) multilayers with vanishing magnetization were grown using magnetron sputtering. Using X-ray microscopy XMCD-PEEM and STXM, we observe chiral Néel domain walls as well as SAF skyrmions at zero external field and room temperature, with average diameters of 200 nm. By employing the corresponding X-ray energy, we are able to resolve the skyrmions in the different SAF layers and demonstrate their AF alignment. Magnetic microscopy , micromagnetic simulations and an analytical model confirm the SAF skyrmion homochirality and allow the identification of the physical parameters controlling their size and stability. We also show that the SAF skyrmions can be nucleated at zero magnetic field using local current injection as well as ultrafast laser excitations. These results pave the way for the use of SAF skyrmions in skyrmion based devices.