Depinning behavior of the vortex domain wall at the asymmetric triangular notch in permalloy wires

The depinning field (H _D) of vortex domain walls in a permalloy wire with an asymmetric triangle notch was investigated through magneto-optic Kerr effect (MOKE) microscopy and micromagnetic simulations. Wires of various widths with notches fixed on the wall's incoming side angle were studied for various outgoing side angles (ϕ). The curves of H _D of wall versus ϕ were measured by MOKE microscopy. Micromagnetic simulations were used to obtain curves of the H _D of the wall versus ϕ. The maximum of such a curve of tail-to-tail -clockwise wall is known as the transition angle (ϕ _T). The shape-anisotropic energy (E _A) of the notch outgoing side wire and the exchange energy (E _Ex) of the wall–notch interaction competed to influence the ϕ _T value. Pinning potential was increased by the E _Ex when ϕ was smaller than the ϕ _T. Pinning potential was considerably reduced by the small E _A when ϕ was larger than the ϕ _T. Furthermore, the ϕ _T value changed with the decrease in the depth of the notch because E _A was influenced by notch depth. (paper)