Nanoscale spin reversal and magnetization growth in GdFeCo studied by ultrafast time-resolved X-ray diffraction

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Advances in magnetic data storage technologies have been fueled by the continuous shrinking of magnetic bit sizes down to a few nanometers (nm), yet identifying deterministic switching mechanisms and speed limits remains a key obstacle to further progress. Current technologies which use magnetic fields or spin-polarized currents to reverse magnetic bits are limited to timescales of ∼100 picoseconds (ps). This apparent speed limit makes spin reversal by femtosecond (fs) optical laser pulses appealing. While fs optical pulses typically induce loss of magnetic order, or demagnetization, in ferromagnetic systems, they can induce macroscopic magnetization reversal in the ferrimagnetic thin film alloy GdFeCo. However, a microscopic picture of this magnetization reversal remains elusive. In this thesis, I will present ultrafast x-ray diffraction experiments with an x-ray laser that probe the nanoscale spin dynamics in GdFeCo following optical excitation. Our results show that the GdFeCo thin film is inhomogeneous, displaying chemical and magnetic structure at ∼10nm which affect the spin dynamics. We observe nanoscale Gd spin reversal after ∼1ps within chemically Gd rich areas of the thin film, despite macroscopic demagnetization. We observes this spin reversed region growing in size for several ps, suggesting that macroscopic switching is initiated within Gd rich nanoregions. The robustness of the spin reversal despite demagnetization indicates that this mechanism could be an effective tool for controlling laser-excited spins in nanostructured materials, opening the door to dramatically faster magnetic recording technologies.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2014
Issuance monographic
Language English


Associated with Graves, Catherine Elizabeth
Associated with Stanford University, Department of Applied Physics.
Primary advisor Kasevich, Mark A
Primary advisor Stöhr, Joachim
Thesis advisor Kasevich, Mark A
Thesis advisor Stöhr, Joachim
Thesis advisor Dürr, Hermann, 1961-
Thesis advisor Fisher, Ian R. (Ian Randal)
Advisor Dürr, Hermann, 1961-
Advisor Fisher, Ian R. (Ian Randal)


Genre Theses

Bibliographic information

Statement of responsibility Catherine Elizabeth Graves.
Note Submitted to the Department of Applied Physics.
Thesis Thesis (Ph.D.)--Stanford University, 2014.
Location electronic resource

Access conditions

© 2014 by Catherine Elizabeth Graves
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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