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Design, fabrication, and characterization of magnetic nanostructures

Design, fabrication, and characterization of magnetic nanostructures
Design, fabrication, and characterization of magnetic nanostructures
For several years, thin films of ferromagnetic materials with metallic spacer layers showing giant magnetoresistance (GMR) were the technological basis used in the read-heads of hard disk drives. Similarly, tunnelling magnetoresistance (TMR), which is an effect typically larger than giant magnetoresistance, occurs when the metallic spacer layers are substituted by an insulating layer. Read-heads based on tunnelling magnetoresistance have been available to the consumer market for the last couple of years. Furthermore, nonvolatile random access memories, also known as magnetic random access memory (MRAM) have also been possible thanks to the use of the tunnelling magnetoresistance effect and have recently been introduced to the consumer market. These technological advances have been possible thanks to years of extensive study and optimization devoted to such effects. Following this logic, we arrive at the conclusion that an effect that produces higher magnetoresistance ratios but uses lower magnetic fields or even only electric currents is highly desired and could be useful for the design and fabrication of spintronic devices of tomorrow.
In this thesis, the use of electron beam lithography (EBL) and a bilayer liftoff process to fabricate magnetic Ni nanostructures with constrictions in the range of 12 to 60 nm is reported. These structures were fabricated based upon the constricted nanowire (CNW) and nanobridge (NB) geometries. High control and reproducibility in the fabrication of such geometries have been achieved with the introduced bilayer liftoff process. This is important because it provides the opportunity to study the statistics of the domain wall magnetoresistance (DWMR) effect and assess its reproducibility.
Additionally, micromagnetic simulations of the fabricated structures were carried out and it was found that domain walls (DWs) with reduced widths down to 48 and 42.5 nm, can be achieved using the CNW and NB geometries, respectively. The magnetoresistance effect due to the presence of a DW has been estimated using dimensions achieved experimentally. Furthermore, the anisotropic magnetoresistance (AMR) effect was obtained numerically and it was found to be smaller than DWMR. This opens the possibility of using the fabricated structures for more systematic studies of DWMR.
Claudio Gonzalez, David
c8cf5efd-0857-4860-8931-b46ca75abdfd
Claudio Gonzalez, David
c8cf5efd-0857-4860-8931-b46ca75abdfd
De Groot, Cornelis
92cd2e02-fcc4-43da-8816-c86f966be90c

Claudio Gonzalez, David (2008) Design, fabrication, and characterization of magnetic nanostructures. University of Southampton, School of Electronics and Computer Science, Doctoral Thesis, 138pp.

Record type: Thesis (Doctoral)

Abstract

For several years, thin films of ferromagnetic materials with metallic spacer layers showing giant magnetoresistance (GMR) were the technological basis used in the read-heads of hard disk drives. Similarly, tunnelling magnetoresistance (TMR), which is an effect typically larger than giant magnetoresistance, occurs when the metallic spacer layers are substituted by an insulating layer. Read-heads based on tunnelling magnetoresistance have been available to the consumer market for the last couple of years. Furthermore, nonvolatile random access memories, also known as magnetic random access memory (MRAM) have also been possible thanks to the use of the tunnelling magnetoresistance effect and have recently been introduced to the consumer market. These technological advances have been possible thanks to years of extensive study and optimization devoted to such effects. Following this logic, we arrive at the conclusion that an effect that produces higher magnetoresistance ratios but uses lower magnetic fields or even only electric currents is highly desired and could be useful for the design and fabrication of spintronic devices of tomorrow.
In this thesis, the use of electron beam lithography (EBL) and a bilayer liftoff process to fabricate magnetic Ni nanostructures with constrictions in the range of 12 to 60 nm is reported. These structures were fabricated based upon the constricted nanowire (CNW) and nanobridge (NB) geometries. High control and reproducibility in the fabrication of such geometries have been achieved with the introduced bilayer liftoff process. This is important because it provides the opportunity to study the statistics of the domain wall magnetoresistance (DWMR) effect and assess its reproducibility.
Additionally, micromagnetic simulations of the fabricated structures were carried out and it was found that domain walls (DWs) with reduced widths down to 48 and 42.5 nm, can be achieved using the CNW and NB geometries, respectively. The magnetoresistance effect due to the presence of a DW has been estimated using dimensions achieved experimentally. Furthermore, the anisotropic magnetoresistance (AMR) effect was obtained numerically and it was found to be smaller than DWMR. This opens the possibility of using the fabricated structures for more systematic studies of DWMR.

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Published date: October 2008
Organisations: University of Southampton

Identifiers

Local EPrints ID: 66279
URI: https://eprints.soton.ac.uk/id/eprint/66279
PURE UUID: c42fc108-2442-49f9-a2a2-25b211039f17
ORCID for Cornelis De Groot: ORCID iD orcid.org/0000-0002-3850-7101

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Date deposited: 28 May 2009
Last modified: 06 Jun 2018 12:49

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Contributors

Author: David Claudio Gonzalez
Thesis advisor: Cornelis De Groot ORCID iD

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