Laser-induced nucleation of magnetic hopfions

Hopfions are three-dimensional topological solitons formed by closed loops of vortex strings, typically taking the shape of rings. In magnetic crystals, hopfions have so far been observed only in unusual configurations, where hopfion rings are linked to skyrmion strings. Although theory predicts the existence of stable, isolated hopfions, their experimental realization has remained elusive. Here, we report the laser-induced nucleation and direct observation of isolated magnetic hopfions in cubic chiral magnets using transmission electron microscopy. The nucleation conditions are mapped out as a function of laser fluence and external magnetic field. Good agreement between experimental data and micromagnetic simulations unambiguously confirms the emergence of isolated hopfions and reveals their detailed structure. We derive the topological invariant for hopfions under realistic rather than idealized boundary conditions, and calculate its integer values for the observed objects. We also demonstrate that hopfions can coexist and interact with other topological spin textures over a broad field range. These findings establish a contact-free approach for nucleating and controlling complex three-dimensional magnetic hopfions, opening new directions for both fundamental research and potential applications.