VP12-09 Dipolar Field-assisted Domain Wall Depinning in Trilayer Structures
Creators: Xingtai Chen
Wenqing Liu
Matthew T Bryan
Publisher: name: IEEE
Year: 2025

Control over domain wall (DW) positioning in nanoscale magnetic structures is fundamental to racetrack memory.1 Pinning strength in a planar nanowire can be tailored by varying notches,2 this approach limits device performance due to Walker breakdown when moving DW undergo changes in magnetization.3 To suppress Walker breakdown, 3D systems like cylindrical and trilayer structures have been developed.4,5 Cylindrical geometries are challenging to produce using planar lithographic techniques, hindering integration with peripheral electronics infeasible. Previously, we showed that trilayers can mimic dynamic behavior seen in nanotubulars, allowing standard manufacturing to access the novel properties of curved geometries.5 Here, we reveal an intriguing pinning behavior of the dipolar-coupled DW from notches in a trilayer structure, showing that pining strength can be propagation order-dependent. Trilayers consisting of 2 nm Permalloy/1 nm spacer/2 nm Permalloy (100 nm width) were modelled with triangular notches using OOMMF. Coupling DWs in the top and bottom layers exhibited opposing magnetizations, resulting in either clockwise (CW) [Fig. 1(a)] or anti-clockwise (ACW) [Fig. 1(b)] circulation. Three distinct phases occurred when propagating DWs toward a notch: no depinning (P0), only one wall depinning (P1), and both walls depinning (P2). Depinning thresholds in the trilayer were lower than in isolated layers, due to the transverse component of the stray field. The notch, acting as a magnetization filter, strongly influenced the transition field from P1 to P2. The P1-P2 boundary required up to 170% higher fields for CW wall pairs than ACW walls [Fig. 1(c-d)], due to flux closure effect, which induced a slight offset between individual walls within the trilayer, influencing the magnetization of the leading wall. Our findings underscore the necessity of considering stray field and flux closure effects when studying DW dynamics in 3D nanowires, as these phenomena cannot be directly extrapolated from single-layer systems.References: 1. S.S.P.P. Parkin, M. Hayashi, and L. Thomas, Science, 320 (5873), 190 (2008) 2. D.M. Burn, and D. Atkinson, Sci Rep 6, 34517 (2016) 3. H. Tanigawa, T. Koyama, and M. Bartkowiak, Phys Rev Lett 101, 207203 (2008) 4. J.A. Fernandez-Roldan, A. De Riz, and B. Trapp, Sci Rep 9, 5130 (2019) 5. X. Chen, T.J. Hayward, and W. Liu, J. Appl. Phys. 130, 223901 (2021)
Control over domain wall (DW) positioning in nanoscale magnetic structures is fundamental to racetrack memory.1 Pinning strength in a planar nanowire can be tailored by varying notches,2 this approach limits device performance due to Walker breakdown when moving DW undergo changes in magnetization.3 To suppress Walker breakdown, 3D systems like cylindrical and trilayer structures have been developed.4,5 Cylindrical geometries are challenging to produce using planar lithographic techniques, hindering integration with peripheral electronics infeasible. Previously, we showed that trilayers can mimic dynamic behavior seen in nanotubulars, allowing standard manufacturing to access the novel properties of curved geometries.5 Here, we reveal an intriguing pinning behavior of the dipolar-coupled DW from notches in a trilayer structure, showing that pining strength can be propagation order-dependent. Trilayers consisting of 2 nm Permalloy/1 nm spacer/2 nm Permalloy (100 nm width) were modelled with triangular notches using OOMMF. Coupling DWs in the top and bottom layers exhibited opposing magnetizations, resulting in either clockwise (CW) [Fig. 1(a)] or anti-clockwise (ACW) [Fig. 1(b)] circulation. Three distinct phases occurred when propagating DWs toward a notch: no depinning (P0), only one wall depinning (P1), and both walls depinning (P2). Depinning thresholds in the trilayer were lower than in isolated layers, due to the transverse component of the stray field. The notch, acting as a magnetization filter, strongly influenced the transition field from P1 to P2. The P1-P2 boundary required up to 170% higher fields for CW wall pairs than ACW walls [Fig. 1(c-d)], due to flux closure effect, which induced a slight offset between individual walls within the trilayer, influencing the magnetization of the leading wall. Our findings underscore the necessity of considering stray field and flux closure effects when studying DW dynamics in 3D nanowires, as these phenomena cannot be directly extrapolated from single-layer systems.References: 1. S.S.P.P. Parkin, M. Hayashi, and L. Thomas, Science, 320 (5873), 190 (2008) 2. D.M. Burn, and D. Atkinson, Sci Rep 6, 34517 (2016) 3. H. Tanigawa, T. Koyama, and M. Bartkowiak, Phys Rev Lett 101, 207203 (2008) 4. J.A. Fernandez-Roldan, A. De Riz, and B. Trapp, Sci Rep 9, 5130 (2019) 5. X. Chen, T.J. Hayward, and W. Liu, J. Appl. Phys. 130, 223901 (2021)