Electric Control of Skyrmion Dynamics and Spin Torque Oscillators in Magnetic Materials with Inversion Asymmetry
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- Institutt for fysikk 
In this thesis the skyrmion velocity in the presence of spin-transfer torques, Rashba spin-orbit coupling and a constant electric field gradient is derived analytically based on a collective coordinate approach in the Thiele formalism. This analytical result is also derived in the presence of a phenomenological pinning force. The results show that the spin-orbit coupling can be effectively considered as a modification of the non-adiabatic spin-transfer torque. The electric field gradient causes a motion of the skyrmion along equipotential lines, in addition to a damped motion in the opposite direction of the gradient to a lower energy state. The analytical calculations are compared to a full numerical solution of the Landau-Lifshitz-Gilbert equation. We also study the effects of Rashba spin-orbit coupling on magnetic multilayer spin torque oscillators. It is discovered that the spin-orbit coupling can be compared to a modification of the Gilbert damping, to the extent that we can get an anti-damping term in the Landau-Lifshitz-Gilbert-Slonczewski equation. This anti-damping term can help destabilize collinear states, and increase the size of the oscillating phase. Moreover, we find an oscillating phase in both ferromagnetically and antiferromagnetically coupled magnetic moments, where the moments are of equal magnitude, which is a new result. The Rashba spin--orbit coupling also allows for a wider tunability of frequency spectra of the spin torque oscillators.