Studying Laser-Induced Spin Currents Using Ultrafast Extreme Ultraviolet Light

Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. Next-generation magnetic-memory devices and heat-assisted magnetic-recording applications will require a better understanding of magnetic multilayers and their interactions with optical-laser pulses. In this thesis, by combining the advantages of ultrabroad-band extreme-ultraviolet light including ultrafast time resolution, element selectivity and tabletop easy access, I report three findings in the study of ultrafast magnetization dynamics in itinerant ferromagnets. First, I experimentally prove that the transverse magneto-optical Kerr response with extreme-ultraviolet light has a purely magnetic origin and that our experimental technique is an artifact-free ultrafast magnetic probe. Second, I demonstrate the first ultrafast magnetization enhancement driven by ultrafast spin currents in Ni/Ru/Fe multilayers. Third, I engineer the sample system by choosing either insulating or spin-scattering spacer layers between the Ni and Fe magnetic layers and by structural ordering. Then, I control the competition between ultrafast spin-flip scattering and superdiffusive spin-current mechanisms; either of these processes may to be the dominant mechanism in ultra-fast demagnetization. Finally, I report two continuing experiments that are promising for future ultrafast magnetization studies with extreme-ultraviolet sources. These experiments are resonant-magnetic small-angle-scattering and the generation of bright circularly polarized high harmonics accompanied by a demonstration of the first x-ray magnetic circular dichroism with a tabletop system. To my wife Esma and my daughter Zeynep Semra. v Acknowledgements First of all, I would like to thank my advisors, Margaret Murnane and Henry Kapteyn, for not only granting me to work in their research group but also supporting, trusting, and challenging me through out graduate school. Then, I thank to Tom Silva for being my third virtual advisor who is a great source of knowledge about magnetism and a great mind for difficult problems. Next, I thank Chan La-o-Vorakiat, the former graduate student, who built the setup and taught me how the experiment works. Moreover, it was a pleasure to work with the magnetism team in Kapteyn-Murnane group including Patrik Grychtol, Ronny Knut, and Dmitry Zusin who is taking over the project bravely. I am also very grateful to our collaborators Technology where we get all wonderful samples with great generosity. For very recent excitement about circularly polarized harmonics, I thank Oren Cohen and Ofer Kfir from Technion University. I am also grateful other members …