Imaging of spin torque switching and ultrafast spectroscopy at X-ray free electron lasers
Abstract/Contents
- Abstract
- In this thesis, I present the results of two distinct sets of experiments relating to x-ray measurements performed on solid metal transmission samples. In the first part, I present time-resolved scanning transmission x-ray microscopy (STXM) measurements that were performed to study the current-induced magnetization switching mechanism in nanopillars exhibiting strong perpendicular magnetic anisotropy. The switching in these devices occurs in the relative alignment (anti-paralllel or parallel) between two ferromagnetic layers: a fixed and free layer. The STXM technique provides both short-time (70 ps) and high-spatial (25 nm) resolutions. Direct imaging of the magnetization demonstrates that, after an incubation time of 1.3ns, a 100nm x 300 nm ellipsoidal device starting in an antiparallel configuration switches in 1 ns via a central domain nucleation and opposite propagation of two domain walls toward the edges. High domain-wall velocities on the order of 100 m/s are measured. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight into magnetization dynamics during the incubation and reversal periods. For the reverse process, from parallel to antiparallel, the situation is less clear, however I can surmise that switching still occurs via domain wall but with less certainty in the location of nucleation. In the second half of the thesis, I explore x-ray absorption spectroscopy at free- electron lasers (FEL). First, I demonstrate the feasibility of near edge x-ray absorption fine structure spectroscopy (NEXAFS) on solids by means of femtosecond soft x-ray pulses from the free-electron laser at hamburg (FLASH). The experiments used a special sample geometry, spectrographic energy dispersion, single shot position- sensitive detection, and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example, I present a NEXAFS spectrum recorded the 3D1 N4,5 edge absorption resonance of La3+ ions in LaMnO3. Later experiments, done at the Linac Coherent Light Source (LCLS), aim to understand the role of electronic damage under intense x-ray pulses. I wish to understand the point at which an intense x-ray pulse can no longer be treated as a small perturbation on the electronic structure of a sample. Because of problems with the normalization of the detection scheme used in the first soft x-ray spectrometer at LCLS, I cannot answer this question definitively, however, initial data is discussed.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2012 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Bernstein, David Paul |
|---|---|
| Associated with | Stanford University, Department of Applied Physics |
| Primary advisor | Fisher, Ian R. (Ian Randal) |
| Primary advisor | Stöhr, Joachim |
| Thesis advisor | Fisher, Ian R. (Ian Randal) |
| Thesis advisor | Stöhr, Joachim |
| Thesis advisor | Bucksbaum, Philip H |
| Advisor | Bucksbaum, Philip H |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | David Paul Bernstein. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2012. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2012 by David Paul Bernstein
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Also listed in
Loading usage metrics...