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

Abstract

The correct identification of topological magnetic objects in experiments is an important issue. In the present work we report on the characterization of metastable skyrmionic spin structures with various topological charges (Q = −3, −2, −1, 0, +1, +2) in the (Pt1−xIrx)Fe/Pd(111) ultrathin magnetic film by performing spin-polarized scanning tunneling microscopy (SP-STM) calculations. We find that an out-of-plane magnetized tip already results in distinguished SP-STM contrasts for the different skyrmionic structures corresponding to their symmetries. Our work also establishes an understanding of the relationship between in-plane SP-STM contrasts and skyrmionic topologies through an investigation of the variation of the in-plane angle between the spins along the perimeter of the structures, which can be characterized by the local vorticity or linear density of the winding number. For spin structures exhibiting a uniform sign of the local vorticity throughout the whole skyrmionic area, we demonstrate that (i) |Q| can be determined from a single SP-STM image taken by any in-plane magnetized tip, and (ii) an in-plane tip magnetization rotation provides the sign of Q independently of the sign of the effective spin polarization in the tunnel junction. We also discuss cases where the local vorticity is changing sign. Finally, by increasing the Ir content of the PtIr overlayer, we find an appearing secondary outer ring in-plane SP-STM contrast that is indicative of attractive skyrmions or antiskyrmions.

Interpretation of experimental evidence of the topological Hall effect

“…Stable ground-state skyrmions were predicted [1] to form in materials lacking inversion symmetry due to a non-centrosymmetric crystal lattice structure [2,3] or due to antisymmetric exchange interactions that occur near the symmetry breaking magnetic interfaces [4]. The skyrmion phase can be observed by Lorentz transmission electron microscopy [5][6][7], magnetic force microscopy [8], Kerr microscopy [9,10], spinpolarized scanning tunneling microscopy (SPSTM) [11,12], spin-polarized low energy electron microscopy (SPLEEM) [13] and neutron scattering [14][15][16]. However, the largest share of the reported experimental evidence is based on the topological Hall effect.…”

Spin Polarized Stm Imaging of Nanoscale Néel Skyrmions in an Sriro3/Srruo3 Perovskite Bilayer

“…|For noncentrosymmetric thin film systems with interfacial DMI, SPSTM simulations have recently elucidated the range of contrast depending on texture topology and tip orientation. 11 We formed a trivial bubble texture by joining two Néel domain walls along a line, and find that simulated SPSTM images also show bright contrast for an OP tip.…”

Skyrmion-antiskyrmion droplets in a chiral ferromagnet

“…Textures with skyrmion and antiskyrmion parts ("chimera skyrmions"), similar to the ones reported here, have been found numerically and studied in Refs. [14,17,18] within a model with frustrated isotropic exchange interaction and DM interaction. Related to our droplet are also the Q = 0 magnetic bubbles reported in Ref.…”