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Magnetic domain wall curvature induced by wire edge pinning

Abstract : In this study we report on the analysis of magnetic domain wall (DW) curvature due to magnetic field induced motion in Ta/CoFeB/MgO and Pt/Co/Pt wires with perpendicular magnetic anisotropy. In wires of 20µm and 25µm a large edge pinning potential produces the anchoring of the DWs ends to the wire edges which is evidenced as a significant curvature of the DW front as it propagates. As the driving magnetic field is increased the curvature reduces as the result of the system moving away from the creep regime of DW motion, which implies a weaker dependence of the DW dynamics on the interaction between the DW and the wire edge defects. A simple model is derived to describe the dependence of the DW curvature on the driving magnetic field and allows to extract the parameter σ E which accounts for the strength of the edge pinning potential. The model describes well systems with both weak and strong bulk pinning potentials like Ta/CoFeB/MgO and Pt/Co/Pt, respectively. This provides a means to quantify the effect of edge pinning induced DW curvature in magnetic DW dynamics. Keywords: magnetic micro wires, domain wall curvature, perpendicular magnetic anisotropy, Understanding the behaviour of magnetic domain walls (DWs) when transitioning from full films into patterned structures is of great importance for developing nanodevices for DW based technologies 1. The analysis of DW dynamics in the so called creep regime of motion 2-5 , where defects play a central role, is a key aspect. In Ta/CoFeB/MgO/Ta films with perpendicular anisotropy bulk defect densities, and therefore depinning fields (H dep), are relatively low 6-8. In Pt/Co/Pt films, for example, the values of H dep can be more than one order of magnitude higher 2,4,5. Due to this low bulk pinning potential the DW dynamics can be easily controlled even in full films by artificial pinning imposed through homogeneous material engineering processes, like light ion irradiation 9-11 or pre-patterned substrates 12. Defects generated through micro/nanostructuring can also have a great impact in pristine materials. DW velocities even in micrometer size wires have been found to experience a critical decrease below the creep law dependence at low drive which scales with the wire width 13. This effect is also accompanied by an increase in the curvature of the DW front and has therefore been attributed to edge pinning. A deeper analysis of the DW curvature in wires is therefore needed in view of miniaturisation for technological applications. In this study we present the analysis of the DW curvature in a series of 20µm wide Ta/CoFeB/
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Contributor : Liza Herrera Diez <>
Submitted on : Wednesday, October 7, 2020 - 7:11:15 PM
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L Herrera Diez, F Ummelen, V Jeudy, G Durin, L Lopez-Diaz, et al.. Magnetic domain wall curvature induced by wire edge pinning. Applied Physics Letters, American Institute of Physics, 2020, 117 (6), ⟨10.1063/5.0010798⟩. ⟨hal-02960638⟩



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