Magnetic behavior of 360° domain walls in patterned magnetic thin films

360° transverse domain walls (360DWs), which form readily from transverse 180° domain walls (180DWs) of opposite sense, demonstrate qualitatively distinct behaviors from their constituent 180DWs and are therefore of interest both from a physics perspective and for their applications in future domain wall devices. This thesis presents experimental and modeling-based investigation of the properties and behaviors of 360DWs including formation, magnetostatic behaviors, and response to field, AC, and DC driving forces. The formation of 360DWs is first examined by simulation in a model nanowire. An injection system capable of producing 360DWs from a wire and an injection pad is presented and its behavior is analyzed both by simulation and experimentally through magnetic force microscopy and scanning electron microscopy with polarization analysis. Next, a model multilayer system is used to demonstrate the magnetostatic behavior of 360DWs, demonstrating a much reduced stray field compared to 180DWs and a strong interlayer pinning behavior that allows the 360DW to act as a programmable pinning site. The richness of this magnetostatic behavior is analyzed experimentally in a rhombic ring system which readily generates 360DWs during reversal. The action of 360DWs is shown to dominate the reversal process, reducing switching fields and showing multiple reversal pathways with a strong dependence on field history. Simulations are used to explore the response of the 360DW to field and DC and AC currents. This highlights 360DW behaviors quite distinct from those of 180DWs, including the inability to be positioned by an applied field and the ability to be destroyed in place. 360DWs are shown to have an intrinsic resonant behavior in the GHz range, the exact frequency of which is broadly tunable by an applied field. Resonance can be excited by an applied AC current, and in conjunction with DC can be used to pin and gate 360DW propagation at a geometric pinning site, using globally applied currents and without impact on nonpinned domain walls.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2012

Author dc:creator

• Mascaro, Mark Daniel

Advisor dc:contributor.advisor

• Caroline Ross.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/76357

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/76357