Laser-induced magnetic nanostructures with tunable topological properties.

We report the creation and real-space observation of magnetic structures with well-defined topological properties and a lateral size as low as about 150 nm. They are generated in a thin ferrimagnetic film by ultrashort single optical laser pulses. Thanks to their topological properties, such structures can be classified as Skyrmions of a particular type that does not require an externally applied magnetic field for stabilization. Besides Skyrmions, we are able to generate magnetic features with topological characteristics that can be tuned by changing the laser fluence. The stability of such features is accounted for by an analytical model based on the interplay between the exchange and the magnetic dipole-dipole interactions.