Nanoscale and ultrafast imaging of magnetic materials with resonant soft X-rays [electronic resource]

Magnetic materials are of interest in a wide range of nanotechnologies including those for data storage, memory, logic, and sensing applications. In addition to going smaller for miniaturization and higher densities, there is also interest in exploring faster processes and pathways to manipulate magnetism. These naturally lead to motivations in studying nanoscale and ultrafast magnetism. Resonant soft x-ray scattering and imaging are unique techniques that can combine nanometer spatial resolution and femtosecond time resolution in the study of magnetic materials. In this dissertation, I will first motivate the need for nanoscale and ultrafast studies on magnetic materials. I will then introduce the attractive properties of soft x-rays, and illustrate the critical concepts in resonant x-ray magnetic scattering and holographic imaging. The three subsequent experiments presented here utilize resonant soft x-rays to image and study magnetic materials. The first experiment demonstrates the use of resonant x-ray scattering in the study of perpendicular magnetic recording media used in hard disk drives. Statistical information on the nanoscale granular and magnetic periodicity of the media can be revealed simultaneously, and we study how various materials parameters are used to optimize the properties of past and current media generations. While scattering provides statistically averaged information, the ability to visualize individual structures is desired. Fourier transform holography is a high resolution and ultrafast-compatible microscopy technique that excels in this role. In the second experiment, I will present our imaging results on all optical magnetic switching, a phenomenon in which magnetic domains of ferrimagnetic alloys are switched with individual, femtosecond laser pulses. Using integrated Au plasmonic dipole antennas to define switching spots, we successfully switched 40 nm-sized magnetic domains in a TbFeCo alloy and prove that all optical magnetic switching is a promising candidate for future information storage technologies. Finally, going into the ultrafast regime, holographic imaging can be combined with x-ray free electron lasers to produce single shot, time-resolved magnetic images. In the last part of this dissertation, I will show the first single shot images of ferromagnetic domain patterns in Co/Pd multilayers taken with 80 fs long x-ray pulses. Despite high x-ray fluences, one can outrun x-ray induced damage effects with short enough pulses. Single shot imaging used in a pump-probe approach can potentially generate stroboscopic movies of magnetization dynamics. The unique combination of nanoscale and ultrafast imaging highlights the versatility and power of resonant soft x-rays in the study of magnetism. The use of such techniques will open up many possibilities for time-resolved studies of magnetic nanostructures and relevant dynamic phenomenon.

Keywords: Materials Science and Engineering.
Advisor: Clemens B. M. (Bruce M.) primary advisor. Thesis advisor
Stöhr Joachim primary advisor. Thesis advisor
Lindenberg Aaron Michael advisor. Thesis advisor