Nanoscale spin structures dominated by magnetoelastic interactions around dislocation cores as seen via spin-polarized STM

We report on studies of spin structures that appear around screw and edge dislocations in Dy (0001) films grown on W (110) substrates. By means of spin-polarized scanning-tunneling microscopy, we have observed the formation of vortexlike and lobe-shaped magnetic structures. We have studied the effect of fundamental dislocations in micromagnetic simulations by including the magnetoelastic interactions in addition to the usually considered energy terms which arise from the magnetocrystalline anisotropy and the exchange energies. Starting from actual physical parameter values for Dy, our calculations are in qualitative and quantitative agreement with the size and the shape of the spin structures experimentally observed.

Figure 1

(a) STM topograph and (b) magnetic signal map of a 90 AL Dy film. The schematic inset summarizes the different magnetic contrast levels which result from different projections of $m_{\text{s}}$ onto $m_{\text{t}}$ calculated as in Ref. 4, The arrows (circles) mark the position where screw (edge) dislocation appear on the surface.

Figure 2

[(a) and (d)] STM topographs and [(b) and (e)] magnetic signal maps of typical screw and edge dislocations, respectively. (c) and (f) are the circular line sections marked in the insets of (b) and (e).

Figure 3

(a) STM topograph and (b) magnetic signal map of a region where an edge dislocation is localized within a single domain. (c) Detail of the neighborhood of the dislocation. (d) Circular line sections marked in (c).

Figure 4

(a) Calculated $dI/dU$ map, using a $250\times 250$ lattice, corresponding to the experimental conditions in Fig. 3. Two level contours are marked upon the lobes for visual purpose. (b) The same as for (a), with stabilizing field (see text for details). (c) Vector plot of the theoretical magnetic moments in the vicinity of the edge dislocation [$75\times 75$ sites, central part of (b)]; for clarity, a simplified mesh is represented. Panels (d) correspond to the circular CCW line sections, in the horizontal axis the angle in degrees starting from the white dots and in the vertical axis the magnetic signal in arbitrary units, shown in (c), at $d=7\text{nm}$ and $d=3.5\text{nm}$.