Imaging of ultrafast phase separation in magnetite and spin injection into copper
Abstract/Contents
- Abstract
- In the recent years, there has been a renewed interest in magnetic materials and correlated oxides due to major advance in thin-film growth technology. Materials showing metal insulator transition with orders of magnitude drop in conductivity, have become a potential candidate for novel electronics and photonics devices. While in data storage, the discovery of Giant Magnetoresistance (GMR) effect has revolutionized read head technology of the hard disk drives. The subsequent investigation of the Spin Transfer Torque phenomenon, promises to be a good candidate for Magnetic Random Access Memory devices. In the first part of my thesis project I focused on the metal insulator transition (Verwey transition) in magnetite triggered by optical excitation. Magnetite, is the first oxide where a relationship between electrical conductivity and fluctuating/localized charges was observed, with a drop in conductivity by two orders of magnitude at 123 K. The Verwey transition is also accompanied by a structural change from monoclinic to cubic symmetry. Recently, three-Fe-site lattice distortions called trimerons have been identified as the true microscopic face of electronic order in low temperature insulating phase. I studied the real time response of insulating magnetite to optical excitation with ultrafast soft X-ray scattering as well as optical pump probe experiments and discovered this to be a two-step process. After an initial femtosecond (300 fs) destruction of individual trimerons in the corresponding lattice, a phase separation into residual insulating trimeron and cubic metallic phases on a 1.5 picosecond timescale is observed. The second part of my thesis project involves understanding spin transport phenomena in spin transfer torque devices with a focus on ferromagnet-paramagnet interface. It has been predicted that near such an interface Copper develops a small nonequilibrium magnetization due to spin accumulation. I use x-ray magnetic circular dichroism to determine the magnitude and the sign of this transient magnetization in Copper. As the induced magnetization is extremely small, I employ time resolved x-ray microscopy to modulate the current on/off signal at MHz rates. Using this technique we have directly imaged the transient magnetization in Copper for the very first time and deduced its magnitude and sign.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2014 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Kukreja, Roopali |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering. |
| Primary advisor | Lindenberg, Aaron Michael |
| Primary advisor | Stöhr, Joachim |
| Thesis advisor | Lindenberg, Aaron Michael |
| Thesis advisor | Stöhr, Joachim |
| Thesis advisor | Reed, Evan J |
| Advisor | Reed, Evan J |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Roopali Kukreja. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2014. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2014 by Roopali Kukreja
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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