Controlling Skyrmion Lattice Orientation with Local Magnetic Field Gradients

Abstract

Precise control over the formation and arrangement of magnetic skyrmion lattices is essential for understanding their emergent behavior and advancing their integration into spintronic and magnonic devices. We report on a simple and minimally invasive technique to nucleate and manipulate skyrmion lattices in soft magnetic CoFeB using single-pass magnetic force microscopy (MFM). By tuning the scan-line spacing to match the intrinsic stripe domain periodicity, the stray field gradient from the MFM tip induces reversible transitions from stripe domains to isolated skyrmions and locally ordered lattices. The resulting skyrmion positions are extracted to compute the local orientational order parameter $ψ_6$, enabling quantitative evaluation of lattice ordering. A systematic improvement in $\langle |ψ_6| \rangle$ is observed with repeated scanning, indicating a transition from a disordered state to ordered hexagonal lattices. Furthermore, we demonstrate that the lattice orientation can be deterministically rotated by changing the scanning direction, as confirmed by both real-space analysis and fast Fourier transformations. This method enables the controlled creation, reordering, and deletion of metastable skyrmion textures on demand. Our approach establishes a practical and accessible platform for studying two-dimensional phase behavior in topological spin systems, offering direct and reconfigurable control over lattice symmetry, order, and orientation.

Figures (4)

• Figure 1: Skyrmion-hosting stack and measurement scheme. (a) Schematic of the ten-repetition ferromagnetic stack. (b) Normalized OOP SQUID magnetometry loop of the continuous multilayers at 300 K. (c) Demagnetized magnetic domain pattern recorded with single-pass MFM. (d) Single-pass procedure to obtain MFM measurements with minimized perturbation by the stray field of the tip.
• Figure 2: Local nucleation and annihilation of magnetic skyrmions by the MFM tip. (a) Transition from the initial maze domain state to a skyrmion state after 5 writing scans, and erasing back to maze domains, driven by scanning the sample in tapping mode with different line spacings $\Delta$. Insets show the corresponding FFTs of the MFM images. Schematic of the process to (b) write skyrmions using $\Delta$$\approx$ 312 nm, closely matched to the domain periodicity, and (c) erase skyrmions by driving skyrmions into annihilation with $\Delta$$\approx$ 10 nm.
• Figure 3: Improving the skyrmion lattice order. (a) Schematic of the local tip-induced repulsion due to antiparallel magnetization used for rearranging skyrmions along the writing direction. (b) Evolution of the mean lattice order parameter $\langle|\psi_6|\rangle$, achieved by rearranging skyrmions after 2, 4, and 10 writing passes. Each circle gives the local order parameter $|\psi_6|$ per skyrmion within the lattice. (c) Ordered skyrmion lattice with $\langle|\psi_6|\rangle$ = 0.7. The dashed white box indicates the region where skyrmions were nucleated and rearranged.
• Figure 4: Rotating the skyrmion lattice orientation. (a) Hexagonal skyrmion lattices written along the horizontal (0$^{\circ}$) direction. (b) The same skyrmion lattice rotated by 90$^{\circ}$ after applying writing scans along the vertical direction. White arrows indicate the fast scan axis directions. (c) Statistical analysis of the orientational angle $\theta$ for skyrmion lattices written along the 0$^{\circ}$ and 90$^{\circ}$ directions.