Exploring magnetism in graphene by electronic charge and spin transport

Magdalena Wojtaszek

Research output: ThesisThesis fully internal (DIV)

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Abstract

The role of ferromagnetic materials in the last century has grown enormously, especially in the data storage technology. Their magnetic properties stem from the ordered arrangement of the spins of electrons. However, the spin ordering can be destroyed by thermal fluctuations, and in fact only three elements: cobalt, nickel and iron are ferromagnetic above room temperature.
After decades of research, it was understood that room-temperature ferromagnetism can exist only in materials having a high concentration of magnetic atoms. Recently, however, there appeared reports claiming ferromagnetism in materials, particularly in graphite, without magnetic elements, questioning the established paradigm. This new type of ferromagnetism is explained by the presence of non-magnetic defects like lattice vacancies and chemisorbed adatoms, but its origin is still debated.
The isolation of graphene, a highly conductive two-dimensional sheet of graphite, brought another carbon allotrope as a testing ground for possible defect-induced magnetism. To verify such magnetism we choose the spin transport technique in nanoscale spin-valve devices. It can diagnose the processes influencing spin coherence, offering an insight into the interactions between spin and possible magnetic moments from defects. This thesis presents a comparative study of spin transport in pristine and defective (hydrogenated) graphene as well as in graphene with an enhanced content of non-zero nuclear spins. Despite leaving the question of defect-induced magnetism in graphene still open to further experimental verification, it provides a versatile toolbox for interpreting spin transport in presence of internal magnetic fields of different origin.
Translated title of the contributionHet verkennen van magnetisme in grafeen met elektrische lading en spin transport
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Groningen
Supervisors/Advisors
  • van Wees, Bart, Supervisor
  • Vera Marun, Ivan, Co-supervisor
  • Roche, Stephan, Assessment committee, External person
  • Esquinazi, Pablo, Assessment committee, External person
  • Ye, Justin, Assessment committee
Award date8-Sep-2014
Place of Publication[S.l.]
Publisher
Print ISBNs978-90-367-7196-2
Electronic ISBNs978-90-367-7195-5
Publication statusPublished - 2014

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