Abstract
Cylindrical magnetic nanowires with large transversal magnetocrystalline anisotropy have been shown to sustain non-trivial magnetic configurations resulting from the interplay of spatial confinement, exchange, and anisotropies. Exploiting these peculiar 3D spin configurations and their solitonic inhomogeneities are prospected to improve magnetization switching in future spintronics, such as power-saving magnetic memory and logic applications. Here we employ holographic vector field electron tomography to reconstruct the remanent magnetic states in CoNi nanowires with 10 nm resolution in 3D, with a particular focus on domain walls between remanent states and ubiquitous real-structure effects stemming from irregular morphology and anisotropy variations. By tuning the applied magnetic field direction, both longitudinal and transverse multi-vortex states of different chiralities and peculiar 3D features such as shifted vortex cores are stabilized. The chiral domain wall between the longitudinal vortices of opposite chiralities exhibits a complex 3D shape characterized by a push out of the central vortex line and a gain in exchange and anisotropy energy. A similar complex 3D texture, including bent vortex lines, forms at the domain boundary between transverse-vortex states and longitudinal configurations. Micromagnetic simulations allow an understanding of the origin of the observed complex magnetic states.
Highlights
Ferromagnetic nanostructures have been widely studied over the past two decades, motivated by the prospect of developing improved spintronic devices based on the physics of magnetic solitons dynamics [1,2,3]
Having completed the detailed description of the magnetization textures in the observed remanent states RS-1 and RS-2 focusing on the domain boundaries/walls occurring in these systems, we investigate the formation energies of the latter
Characteristic zig-zag modulations of the vortex lines are observed for the transverse-vortex states located close to the chain’s extremities, eventually rotating the lines into a longitudinal vortex
Summary
Ferromagnetic nanostructures have been widely studied over the past two decades, motivated by the prospect of developing improved spintronic devices based on the physics of magnetic solitons (e.g., domain walls, bubbles, skyrmions) dynamics [1,2,3]. Localized solitonic configurations of the magnetization in a nanoscale specimen, such as multifarious magnetic domain walls (DWs), generically break spatial parities present in the material This magnetic chirality has important implications for the possibility to exert torques and to drive such configurations, e.g., by electrical currents or by external fields—one of the basic operations of spintronics. A reason for this is a lack of experimental techniques allowing one to probe these complex 3D nanomagnetic configurations with strong hysteretic character down to nanometer resolution and the elusive exploration of solitonic states with solely theoretic tools (micromagnetic simulations) in the presence of unknown parameters such as effective anisotropies, real-structure effects, and unknown details of the magnetic history. By microscopically resolving the magnetic configurations for two RS in such wires, we show that these states resemble earlier suggestions regarding possible ground and metastable states but are considerably more complex, concerning the DWs separating the domains
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