Pattern formation in skyrmionic materials with anisotropic environments

Abstract

Magnetic skyrmions have attracted broad attention during recent years because they are regarded as promising candidates as bits of information in novel data storage devices. A broad range of theoretical and experimental investigations have been conducted with the consideration of rotational symmetric skyrmions in isotropic environments. However, one naturally observes a huge variety of anisotropic behavior in many experimentally relevant materials. In the present work, we investigate the influence of anisotropic environments onto the formation and behavior of the non-collinear spin states of skyrmionic materials by means of Monte-Carlo calculations. We find skyrmionic textures which are far from having a rotational symmetric shape. Furthermore, we show the possibility to employ periodic modulations of the environment to create skyrmionic tracks. PACS numbers:Magnetic skyrmions were originally proposed and investigated in theoretical studies [1,2] and only recently, they were found experimentally in the bulk and thin films of non-centrosymmetric materials [3][4][5][6][7][8][9] as well as in ultra-thin magnetic films at crystal surfaces [10][11][12]. They are particle-like objects with a non-vanishing topological charge that is considered to protect them from continuous transformation into the saturated magnetic state. Together with their small lateral size in the nanometer range, this makes skyrmions an interesting candidate for bits of information and information carriers in novel data storage devices [13,14]. Typically, magnetic skyrmions form due to the competition of the Dzyaloshinskii-Moriya (DM) interaction [15,16] and the exchange interaction in the presence of an external magnetic field. The DM interaction can provide a non-vanishing contribution in the presence of inversion asymmetry combined with a large spin-orbit interaction. The properties of skyrmions have both theoretically and experimentally mainly been investigated in the context of materials providing an isotropic environment up to now which leads to the formation of skyrmions with a rotational symmetric equilibrium shape. There are only few studies that deal with the influence of anisotropic environments and only recently, the experimental observation of skyrmions which are deformed with respect to the rotational symmetric shape has been reported for chiral magnets with crystal lattice strain [17].However, various experimentally feasible materials naturally exhibit anisotropic behavior for multiple reasons. In the discussion of the origins, we focus on the material systems that allow for interface induced skyrmionic states, only. These material systems typically consist of a single or multiple atomic, magnetic layers of different atomic species which are deposited succeedingly onto a non-magnetic supporting crystal. The combination of materials with different lattice constants can give rise to lattice strain and reconstructions in the magnetic surface layers which then exhibit anisotropic environments as has been discussed only recently for the...

Spin-polarized scanning tunneling microscopy characteristics of skyrmionic spin structures exhibiting various topologies

“…This already suggests the presence of a non-uniform sign of the local vorticity. A deeper theoretical analysis puts forward that the observed spin structure is a magnetic skyrmion with |Q| = 1 exhibiting a non-circular shape [37]. It is interesting to note the similarity of the out-of-plane SP-STM contrast of this reported skyrmion and our skyrmion with Q = −2 [see Fig.…”

“…We have to stress that the shape of the magnetic skyrmions formed in anisotropic environments, e.g., in reconstructed films [17,37], considerably affects the local vorticity and, consequently, the observed in-plane SP-STM contrasts. Such an example is an axially nonsymmetric spin structure derived from experimental SP-STM contrasts in Ref.…”

“…A measured series of in-plane SP-STM contrasts are also expected to help in identifying spin structures if the local vorticity is not uniform. Such a scenario is expected in anisotropic environments of skyrmion formation, e.g., in reconstructed or confined film geometries [17,37], where arbitrary skyrmionic shapes with complex domain wall structures can be found.…”

Dzyaloshinskii-Moriya interaction at disordered interfaces from ab initio theory: Robustness against intermixing and tunability through dusting

“…As an example, reconstruction lines in Fe/Ir(111) lead to an alteration of the wavefront of spin spirals 15 and finally to the stabilization of skyrmions that are not axially symmetric 16 .…”

Dynamics of distorted skyrmions in strained chiral magnets

“…It is suggested theoretically that the magnitude of the DM interaction is prominently modulated by the lattice distortion, resulting in the deformation of the skyrmion. Furthermore, distorted skyrmion is suggested to be stabilized in thin films of chiral magnets under tilted magnetic fields and/or with anisotropic environments [26,27].…”