Surface pinning and triggered unwinding of skyrmions in a cubic chiral magnet

Abstract

In the cubic chiral magnet Fe1−xCoxSi a metastable state comprising of topologically nontrivial spin whirls, so-called skyrmions, may be preserved down to low temperatures by means of field cooling the sample. This metastable skyrmion state is energetically separated from the topologically trivial ground state by a considerable potential barrier, a phenomenon also referred to as topological protection. Using magnetic force microscopy on the surface of a bulk crystal, we show that certain positions are preferentially and reproducibly decorated with metastable skyrmions, indicating that surface pinning plays a crucial role. Increasing the magnetic field allows an increasing number of skyrmions to overcome the potential barrier, and hence to transform into the ground state. Most notably, we find that the unwinding of individual skyrmions may be triggered by the magnetic tip itself, however, only when its magnetization is aligned parallel to the external field. This implies that the stray field of the tip is key for locally overcoming the topological protection. Both the control of the position of topologically nontrivial states as well as their creation and annihilation on demand pose important challenges in the context of potential skyrmionic applications.

Evolution of magnetocrystalline anisotropies in Mn1−xFexSi and Mn1−xKindervater1, Adams2, Bauer3 et al. 2020Phys. Rev. B234170View full textAdd to dashboardCite

“…Unfortunately, our small-angle neutron scattering set-up is not sensitive to such short-range effects. However, related magnetic textures were recently observed using magnetic force microscopy in Fe 1−x Co x Si [119,120]. As both Fe 1−x Co x Si and Mn 1−x Fe x Si are subject to similar amounts of structural disorder, and as both compounds display similar hysteresis effects in the susceptibility [37], it seems plausible that the same mechanisms are active in both materials.…”

Evolution of magneto-crystalline anisotropies in Mn$_{1-x}$Fe$_x$Si and Mn$_{1-x}$Co$_x$Si as inferred from small-angle neutron scattering and bulk properties

“…Unfortunately, our small-angle neutron scattering set-up is not sensitive to such short-range effects. However, related magnetic textures were recently observed using magnetic force microscopy in Fe 1−x Co x Si 116,117 . As both Fe 1−x Co x Si and Mn 1−x Fe x Si are subject to similar amounts of structural disorder, and as both compounds display similar hysteresis effects in the susceptibility 37 , it seems plausible that the same mechanisms are active in both materials.…”