Stability, Dynamics, and Nucleation of Magnetic Skyrmions
Thesis Defense
10:00 am –
12:00 pm
Jorgensen Hall Room: 145
Contact:
Physics Department, (402) 472-2770, paoffice@unl.edu
Rabindra Nepal
Advisor: Alexey Kovalev
ABSTRACT:
The possibility of exploiting an extra spin-degree of freedom in current semiconductor-based memory devices, makes the magnetic memory device a promising next generation candidate for memory 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 magnetic systems and in particular the stability and dynamics of magnetic solitons such as domain walls, skyrmions, and antiskyrmionss. This wide interest in the spintronics community has also contributed to uncover the different physical effects and phenomena corresponding to these magnetic quasi-particles in addition to 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.
The 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 systems can lead to stabilization of skyrmions, antiskyrmions, and result in modifications of helicity. We also studied the creation of skyrmions and antiskyrmions 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. We further study current-induced motion of skyrmions and antiskyrmions in a system with a boundary. Our study opens the window of future studies of magnets with engineered DM interaction and can result in new methods of creating skyrmions and antiskyrmions.
Advisor: Alexey Kovalev
ABSTRACT:
The possibility of exploiting an extra spin-degree of freedom in current semiconductor-based memory devices, makes the magnetic memory device a promising next generation candidate for memory 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 magnetic systems and in particular the stability and dynamics of magnetic solitons such as domain walls, skyrmions, and antiskyrmionss. This wide interest in the spintronics community has also contributed to uncover the different physical effects and phenomena corresponding to these magnetic quasi-particles in addition to 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.
The 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 systems can lead to stabilization of skyrmions, antiskyrmions, and result in modifications of helicity. We also studied the creation of skyrmions and antiskyrmions 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. We further study current-induced motion of skyrmions and antiskyrmions in a system with a boundary. Our study opens the window of future studies of magnets with engineered DM interaction and can result in new methods of creating skyrmions and antiskyrmions.