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Stability, Dynamics, and Nucleation of Magnetic Skyrmions

Rabindra Nepal, University of Nebraska - Lincoln

Abstract

The possibility of exploiting an extra spin-degree of freedom, in addition to the only charge-degree of freedom in current semiconductor based memory devices, makes the magnetic memory device a promising next generation candidate for storage applications, especially in light of the saturation of Moore's law. This has led to the burst of research interests in the spin dynamics in the magnetic systems and in particular the stability and dynamics of magnetic solitons such as domain walls, skyrmions and antiskyrmions, and has resulted in the proposal of domain-wall racetrack memory. The wide interest in the spintronics community has also helped to uncover the different physical effects and phenomena corresponding to these magnetic quasi-particles in addition to exploring their applications potential. In this dissertation, we focus on the study of stability and dynamical effects of magnetic domain walls and skyrmions in the presence of various driving mechanisms. We explore the parametric oscillations of a magnetic domain wall pinned on a notch using ac strain and show how such oscillations can be used for the efficient domain wall depinning from the notch or the microwave generation. Similarly, we also study the motion of skyrmion bubble in a ferromagnetic film due to the force generated by strain-gradient induced from the surface-acoustic waves on a piezoelectric substrate. Creation and stability of skyrmions is crucial for any meaningful application. We carried out a detailed analysis of the phase diagram of thin magnetic films and showed how the form of Dzyaloshinskii-Moriya (DM) interaction and symmetry of the system can lead to stabilization of skyrmions, anti-skyrmions, and result in modifications of helicity. We also studied the creation of (anti-)skyrmions from the boundary magnon-mode instabilities, which can be induced by magnetic field and/or charge current pulses. The mechanism of skyrmion creation from boundary instabilities is studied in detail and can be related to the Doppler shift effect induced by charge currents and spin-transfer torques. We further study current-induced motion of skyrmions and anti-skyrmions in a system with a DM interface. Our study opens the window of future studies of magnets with engineered DM interaction and can result in new methods of creating skyrmions and anti-skyrmions.

Subject Area

Physics|Condensed matter physics

Recommended Citation

Nepal, Rabindra, "Stability, Dynamics, and Nucleation of Magnetic Skyrmions" (2019). ETD collection for University of Nebraska - Lincoln. AAI22588295.
https://digitalcommons.unl.edu/dissertations/AAI22588295

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