Skyrmions and spin waves in frustrated ferromagnets at low applied magnetic field

Abstract

A continuum model of frustrated ferromagnets is analyzed in detail in the regime of low applied magnetic field, $H_0<1/4$, where the ground state is a spatially varying conical spiral. By changing variables to a corotating spin field, the model is reformulated as a gauged sigma model in a fixed background gauge, allowing the construction of stable isolated Skyrmions, and stable multi-Skyrmion clusters, which approach the conical ground state at spatial infinity. Owing to the spatial anisotropy induced by the ground state, these Skyrmions exhibit only discrete symmetries, and are of neither Néel nor Bloch type. These Skyrmions are continuously connected to the more familar solutions in the high field regime ($H_0>1/4$), acquiring axial symmetry in the limit $H_0\to 1/4$. The propagation of small amplitude spin waves through the conical ground state is also analyzed and is found to depend strongly on both $H_0$ and propagation direction relative to the ground state. In contrast to spin waves in the high field regime ($H_0>1/4$) there is no spectral gap: waves may propagate with any angular frequency.

arXiv comment18 pages, 9 figures

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• Antichiral Ferromagnetism
• Intervortex forces in competing-order superconductors
• Manipulation and trapping of magnetic skyrmions with domain walls in chiral magnetic thin films
• Vortex lattices and critical fields in anisotropic superconductors
• Domain Wall Networks as Skyrmion Crystals in Chiral Magnets
• Genetic-tunneling driven energy optimizer for spin systems
• Paradoxical Topological Soliton Lattice in Anisotropic Frustrated Chiral Magnets