ISBN 978-3-8439-2963-9

978-3-8439-2963-9, Reihe Physik

Laura Feiler
Nonlinear spin-wave excitation detected by the inverse spin-Hall effect

140 Seiten, Dissertation Universität Hamburg (2016), Softcover, A5

Zusammenfassung / Abstract

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.