Ferromagnetism and resisitive switching in magnesium oxide with nitrogen doping
Abstract/Contents
- Abstract
- Over the past several years, there have been considerable interests in the possibility of creating ferromagnetism in thin films of doped oxide materials. Several systems have been identified to be ferromagnetic at room temperature but all of these systems contain either a transition metal element or a rare earth metal element as a dopant. Since in such systems the formation of second phase or clusters of magnetic ions cannot be ruled out, the origin of ferromagnetism is still controversial. Our interest is exploring the possibility of ferromagnetism existing in the oxide materials. We have chosen to study whether doping alkali earth metal oxides with nitrogen yields ferromagnetic oxides. There are several theoretical predictions that such systems will be ferromagnetic, yet there is no conclusive experimental demonstration of such a finding. In this dissertation, we demonstrate the ferromagnetism in the nitrogen-doped magnesium oxide where the N-dopant does not induce structural defects, where the N-dopant is not a metal, and where oxide is an insulator. We find that as-deposited N-doped MgO films are disordered and non-magnetic. These samples upon thermal annealing undergo a significant structural transformation with doped N atoms moving from interstitial/defect to substitutional sites within MgO lattice and the resulting films are ferromagnetic. The largest magnetic moment measured corresponds to 0.35 [mu]B/per N for the 2.2 at% N-doped MgO film. XPS data indicate the presence of an unpaired electron in 2p orbital of N. The long range spin-interaction of these unpaired N electrons mediated by the valence band of MgO is ferromagnetic. NEXAFS data support this conclusion as hole states are also observed in the O 2p state. These results for first time prove the authenticity of prior theoretical predictions about the possible ferromagnetism in N-doped alkali earth oxides. The second part of this dissertation is focused on the resistive switching in N-doped MgO for memory applications. Resistive switching in thin layers is demonstrated herein, in which the thin layer include MgO doped with a small amount of N. The resistance change ratio (RHigh/RLow) can be varied between 1-4 orders of magnitude by varying the N content with just a few percent. In addition, SET voltage can be systematically lowered by varying the N content of the layer. The resistive switching properties of the N-doped MgO structures have several other attractive features. In particular, resistive switching is demonstrated to occur by applying SET and RESET voltage pulses from 1-100 nsec in duration and to exhibit low RESET current (few tenths of [mu]A). Multi-level resistive switching is also demonstrated. These unique advantages of N-doped MgO are highly desirable for the next generation nonvolatile memory.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2010 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Yang, Cheng-Han |
|---|---|
| Associated with | Stanford University, Department of Materials Science and Engineering |
| Primary advisor | Harris, J. S. (James Stewart), 1942- |
| Primary advisor | Parkin, Stuart S. P |
| Thesis advisor | Harris, J. S. (James Stewart), 1942- |
| Thesis advisor | Parkin, Stuart S. P |
| Thesis advisor | Brongersma, Mark L |
| Advisor | Brongersma, Mark L |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Cheng-Han Yang. |
|---|---|
| Note | Submitted to the Department of Materials Science and Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2010. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2010 by Cheng-Han Yang
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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