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Magnetic skyrmions have attracted substantial interest due to their potential for use in spintronics devices and next-generation information storage, and due to the novel phenomena that result from the topological winding of skyrmions. In this dissertation we theoretically study the properties of magnetic skyrmions in chiral magnets. We focus on two key parameters that must be optimized to achieve maximum device performance: skyrmion size, and skyrmion stability. Skyrmions are stabilized in materials where inversion symmetry is broken. We show that the skyrmion crystal phase is more stable in systems with broken mirror inversion symmetry compared with systems where only bulk inversion symmetry is broken. To understand this effect we study a system where both mirror and bulk inversion symmetry are broken. We show that broken bulk inversion symmetry tends to stabilize a conical phase, and this phase becomes progressively less stable when broken mirror inversion symmetry is introduced. The phase diagram reveals a large region of skyrmion crystal stability, as well as a stable elliptic cone phase, and a square skyrmion crystal phase.In addition to crystal structures with broken inversion symmetry, the presence of an interface in magnetic films introduces a source of broken mirror symmetry. We show that this added source of symmetry breaking enhances the stability of the skyrmion crystal phase. Films surfaces and interfaces also stabilize a novel phase of matter called a chiral bobber crystal. This phase can be uniquely identified by the presence of a two-dimensional lattice of singular points in the magnetization field called Bloch points. We present experimental evidence for the observation of a chiral bobber crystal using magnetization data.Skyrmions can also be found outside the skyrmion crystal phase as metastable, particle-like excitations with a finite lifetime. We show that the lifetime and size of skyrmions have a strong interdependence. Putting limits on the lifetime of a skyrmion also restricts the range of skyrmion sizes. For a given lifetime, the smallest skyrmion size is determined by competition between the exchange interaction and the Dzyaloshinskii-Moriya interaction. We also show that the lifetime of a skyrmion depends essentially on two parameters: the energy of a skyrmion, and the energy of a Bloch point. In two-dimensional systems (magnetic films and interfaces), the Bloch point forms in space-time; in three-dimensional systems, the Bloch point forms totally in space and has the structure of a chiral bobber. Finally, we show that entropic corrections to the lifetime are typically small, except near a special point in the phase diagram where skyrmion size diverges, and soft-modes contribute to a divergence in the entropy of a skyrmion. |
