Torsion-induced effects in magnetic nanowires

Abstract

Magnetic helix wire is one of the most simple magnetic systems which manifest properties of both curvature and torsion. There exist two equilibrium states in the helix wire with easy-tangential anisotropy: a quasi-tangential magnetization distribution in case of relatively small curvatures and torsions, and an onion state in opposite case. In the last case the magnetization is close to tangential one, deviations are caused by the torsion and curvature. Possible equilibrium magnetization states in the helix magnet with different anisotropy directions are studied theoretically. The torsion also essentially influences the spin-wave dynamics, acting as an effective magnetic field. Originated from the curvature induced effective Dzyaloshinskii interaction, this magnetic field leads to the coupling between the helix chirality and the magnetochirality, it breaks mirror symmetry in spinwave spectrum. All analytical predictions on magnetization statics an dynamics are well confirmed by the direct spin lattice simulations.

Magnetization in narrow ribbons: curvature effects

“…The helicoid ribbon has zero effective curvature but finite torsion, which provides a paradigmatic model for studying purely torsion-induced effects. Similar to a microhelix structure [17], a geometry-induced effective DzyaloshinskiiMoriya interaction is a source of coupling between the helicoid chirality and the magnetochirality, which essentially influences both magnetization statics and dynamics. The emergent magnetic field generated by the torsion breaks mirror symmetry, so that the properties of magnetic excitations in different spatial directions is not identical.…”

“…The linearised Landau-Lifshits equations have the form of a generalized Schrödinger equation for the complex-valued function ψ = ϑ + iϕ [17],…”

“…Geometry-induced anisotropy can have a significant effect on the ground-state magnetization profile, rendering it no longer strictly tangential, even in the case of strong easy-tangential anisotropy. For example, for a helical nanowire with strong anisotropy directed along the wire, the ground-state magnetization is always tilted in the local rectifying surface, with tilting angle dependent on the product of the curvature and the torsion [17,18]. For two-dimensional geometries with nontrivial topology, a striking manifestation of geometry-induced anisotropy is shape-induced patterning.…”

Curvature induced magnonic crystal in nanowires

“…Spin waves can be bound by a local bending of the wire [9]. A wire twisting results in non-reciprocal spin-wave propagation [10]. Numerous curvature effects in the domain wall dynamics were found, namely the localized curvature defect (e.g.…”

Magnetization ground state and reversal modes of magnetic nanotori

“…From the theoretical point of view, this interest has been reinforced due to the recent development of a functional that allows to calculate the exchange energy of nanomagnets with arbitrary shapes 15,16 . This functional has been used to study the magnetic properties of non-planar nanomagnets such as Möbius stripes 17 , helical wires 18 and domain walls in a parabolic local bend of a nanowire 19 .…”