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978-3-8439-2963-9, Reihe Physik
Nonlinear spin-wave excitation detected by the inverse spin-Hall effect
140 Seiten, Dissertation Universität Hamburg (2016), Softcover, A5
The investigation of magnetic nanostructures that utilize the spin as an additional degree of freedom became one of the strongly emerging fields in research, since it offers a high potential for new technological applications. In this thesis spin currents in microstructured permalloy/platinum bilayers that are excited via magnetic high-frequency fields are investigated. Due to this excitation, the magnetization of the ferromagnetic permalloy layer precesses at resonance, and at the permalloy/platinum interface a spin current is injected into the platinum layer due to the spin-pumping effect. The spin current is detected as a voltage in the platinum layer via the inverse spin-Hall effect.
In preparation for the voltage measurements the magnetization precession is characterized via broadband-ferromagnetic resonance measurements. They reveal a linear and a dominantly nonlinear damping regime in dependence on the high-frequency excitation field strength. The inverse spin-Hall effect voltages obtained in the spin-transport measurements also feature two regimes reflected by a nonlinear, abrupt voltage surge. This voltage surge is reproducibly observed at distinct excitation field strengths, and can be manipulated by a variation of the sample geometry. Micromagnetic simulations as well as transmission spectrum analyses of the excitation signal show that the surge is caused by the incipient excitation of nonlinear spin-wave modes. These modes precess at the excitation frequency and at its higher harmonics. The comparatively large voltages reveal a highly efficient spin-current generation method in a mesoscopic spintronic device.