Topologically nontrivial spin textures have recently been investigated for spintronic applications. Here, we report on an ultrathin magnetic film in which individual skyrmions can be written and deleted in a controlled fashion with local spin-polarized currents from a scanning tunneling microscope. An external magnetic field is used to tune the energy landscape, and the temperature is adjusted to prevent thermally activated switching between topologically distinct states. Switching rate and direction can then be controlled by the parameters used for current injection. The creation and annihilation of individual magnetic skyrmions demonstrates the potential for topological charge in future information-storage concepts.

The atomic-scale spin structure of individual isolated Skyrmions in an ultrathin film is investigated in real space by spin-polarized scanning tunneling microscopy. Their axial symmetry as well as their unique rotational sense is revealed by using both out-of-plane and in-plane sensitive tips. The size and shape of Skyrmions change as a function of the magnetic field. An analytical expression for the description of Skyrmions is proposed and applied to connect the experimental data to the original theoretical model describing chiral Skyrmions. Thereby, the relevant material parameters responsible for Skyrmion formation can be obtained.

Magnetic skyrmions are localized non-collinear spin textures with a high potential for future spintronic applications. Skyrmion phases have been discovered in a number of materials and a focus of current research is to prepare, detect and manipulate individual skyrmions for implementation in devices. The local experimental characterization of skyrmions has been performed by, for example, Lorentz microscopy or atomic-scale tunnel magnetoresistance measurements using spin-polarized scanning tunnelling microscopy. Here we report a drastic change of the differential tunnel conductance for magnetic skyrmions that arises from their non-collinearity: mixing between the spin channels locally alters the electronic structure, which makes a skyrmion electronically distinct from its ferromagnetic environment. We propose this tunnelling non-collinear magnetoresistance as a reliable all-electrical detection scheme for skyrmions with an easy implementation into device architectures.

An understanding of the pinning of magnetic skyrmions to defects is crucial for the development of future spintronic applications. While pinning is desirable for a precise positioning of magnetic skyrmions it is detrimental when they are to be moved through a material. We use scanning tunneling microscopy (STM) to study the interaction between atomic scale defects and magnetic skyrmions that are only a few nanometers in diameter. The studied pinning centers range from single atom inlayer defects and adatoms to clusters adsorbed on the surface of our model system. We find very different pinning strengths and identify preferred positions of the skyrmion. The interaction between a cluster and a skyrmion can be sufficiently strong for the skyrmion to follow when the cluster is moved across the surface by lateral manipulation with the STM tip.Magnetic skyrmions are particle-like knots in the spin texture which are considered as promising candidates for future spintronic applications [1-3]. They typically arise in materials which have a spin spiral ground state due to the Dzyaloshinskii-Moriya (DM) interaction [4, 5] at zero magnetic field; upon application of an external magnetic field a hexagonal skyrmion lattice phase can occur before the magnetization is saturated. From an analysis of the energies it is known that near the boundary between the lattice phase and the ferromagnetic state also isolated skyrmions can be stabilized, and it has been demonstrated experimentally that also reduced temperature facilitates the preparation of individual skyrmions [6]. Skyrmion lattices have been moved through a material by laterally imprinted currents due to spin transfer torques [7][8][9]. While below a critical current density the periodic magnetic texture is pinned, for larger lateral currents pinning forces were found to be negligible and the skyrmion velocity was proportional to the current [8]. Simulations for skyrmion lattices support this finding and suggest that randomly distributed impurities do not have a significant impact on the velocity under applied currents [10]; however, an influence of the density of magnetic skyrmions on their lateral movement has been proposed [11]. For individual magnetic skyrmions several different pinning mechanisms have been considered theoretically, ranging from a combined increase of magnetic exchange and DM interaction [12], over vacancies in the magnetic material [13], to repulsive interaction due to areas with higher magnetic anisotropy [14]. The conclusion from these studies is that depending on the parameters both the movement around a defect and the capturing of a skyrmion at a pinning site is possible.Here we study pinning in the model system of the PdFe atomic bilayer on Ir(111) [6,15,16]. Using scanning tunneling microscopy (STM) we investigate the interaction of non-collinear magnetic states with different atomic-scale defects. We find that single magnetic skyrmions can be significantly distorted due to their interaction with clusters adsorbed on the surface. Furthermore the ...

We investigate the impact of the local spin texture on the differential conductance by scanning tunneling microscopy. In the focus is the previously found non-collinear magnetoresistance, which originates from spin mixing effects upon electron hopping between adjacent sites with canted magnetic moments. In the present work it is studied with lateral resolution both for the zero magnetic field spin spiral state as well as for individual magnetic skyrmions at different magnetic field values. We analyze in detail the response of the differential conductance and find different dependencies of peak energy and peak intensity on the local properties of the non-collinear spin texture. We find that in the center of a skyrmion the peak energy and intensity scale roughly linear with the angle between nearest neighbor moments. Elsewhere in the skyrmion, where the non-collinearity is not isotropic and the magnetization quantization axis varies, the behavior of the peak energy is more complex.

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