Understanding the motion of magnetic skyrmions is essential if they are to be used as information carriers in devices. It is now shown that topological confinement endows the skyrmions with an unexpectedly large mass, which plays a key role in their dynamics. Skyrmions are topologically protected winding vector fields characterized by a spherical topology1. Magnetic skyrmions can arise as the result of the interplay of various interactions, including exchange, dipolar and anisotropy energy in the case of magnetic bubbles2,3,4 and an additional Dzyaloshinskii–Moriya interaction in the case of chiral skyrmions5. Whereas the static and low-frequency dynamics of skyrmions are already well under control6,7,8,9, their gigahertz dynamical behaviour2 has not been directly observed in real space. Here, we image the gigahertz gyrotropic eigenmode dynamics of a single magnetic bubble and use its trajectory to experimentally confirm its skyrmion topology. The particular trajectory points to the presence of strong inertia, with a mass much larger than predicted by existing theories. This mass is endowed by the topological confinement of the skyrmion and the energy associated with its size change. It is thereby expected to be found in all skyrmionic structures in magnetic systems and beyond. Our experiments demonstrate that the mass term plays a key role in describing skyrmion dynamics.

Ultrashort, coherent x-ray pulses of a free-electron laser are used to holographically image the magnetization dynamics within a magnetic domain pattern after creation of a localized excitation via an optical standing wave. We observe a spatially confined reduction of the magnetization within a couple of hundred femtoseconds followed by its slower recovery. Additionally, the experimental results show evidence of a spatial evolution of magnetization, which we attribute to ultrafast transport of nonequilibrium spin-polarized electrons for early times and to a fluence-dependent remagnetization rate for later times.

Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate this, we perform a joint theoretical and experimental investigation to determine the transient changes of the helicity dependent absorption in the extreme ultraviolet spectral range. We show that the helicity dependent absorption is directly related to changes of the transient spin-split density of states, allowing us to link the origin of OISTR to the available minority states above the Fermi level. This makes OISTR a general phenomenon in optical manipulation of multi-component magnetic systems.

We report the first analysis of the polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system by femtosecond x-ray diffraction. Two Bragg reflections provide information on the coupled dynamics of the two relevant phonon modes for ferroelectricity in perovskites, the tetragonal distortion and the soft mode. Optical excitation of the ${\mathrm{SrRuO}}_3$ metal layers generates giant stress ($>1\mathrm{GPa}$) compressing the ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ layers by up to 2%. The resulting change of tetragonality reaches a maximum after 1.3 ps. As a result, the ferroelectric polarization $P$ is reduced by up to 100% with a slight delay that is due to the anharmonic coupling of the two modes.