Exploring magnetism in graphene by electronic charge and spin transport

Magdalena Wojtaszek

Exploring magnetism in graphene by electronic charge and spin transport

Vertaalde titel van de bijdrage: Het verkennen van magnetisme in grafeen met elektrische lading en spin transport

Magdalena Wojtaszek

Fysica van Nano Devices

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De rol van ferromagnetische materialen is in de afgelopen eeuw enorm gegroeid, met name in de technologie voor dataopslag. Hun magnetische eigenschappen komen voort uit geordende rangschikking van de spins van elektronen. Deze spin ordening kan echter worden verstoord door thermische fluctuaties en in feite zijn er slechts drie elementen ferromagnetisch boven kamertemperatuur: kobalt, nikkel en ijzer.
Na tientallen jaren onderzoek werd begrepen dat ferromagnetisme op kamertemperatuur alleen mogelijk is voor materialen met hoge concentraties magnetische atomen. Maar recentelijk werd er ook ferromagnetisme geclaimd in materialen zonder magnetische elementen, grafiet in het bijzonder, waardoor het gevestigde paradigma in twijfel werd getrokken. Dit nieuwe type ferromagnetisme kan worden verklaard door de aanwezigheid van niet-magnetische defecten, zoals roostervacatures of chemisch geadsorbeerde atomen, maar de oorzaak staat nog altijd ter discussie.
De isolatie van grafeen, een goed geleidende tweedimensionale laag grafiet, leverde een nieuwe koolstof allotroop als testobject voor mogelijk defect geïnduceerd magnetisme. Om een dergelijk magnetisme te verifiëren kozen we voor de spin transport techniek in nanoschaal spin-valve devices. Hierin kunnen processen met invloed op spin coherentie worden gediagnosticeerd, wat inzicht biedt in de interacties tussen spins en magnetische momenten. Dit proefschrift presenteert een vergelijkende studie tussen spin transport in ongerept en defect (gehydrogeneerd) grafeen, maar ook in grafeen met een verhoogde concentratie van nucleaire spin. Ondanks dat de vraag over defect geïnduceerd magnetisme in grafeen open blijft voor verdere experimentele opheldering, wordt een veelzijdige werkset geleverd om spin transport in aanwezigheid van interne magnetische velden van gevarieerde oorsprong te interpreteren.

Vertaalde titel van de bijdrage	Het verkennen van magnetisme in grafeen met elektrische lading en spin transport
Originele taal-2	English
Kwalificatie	Doctor of Philosophy
Toekennende instantie	Rijksuniversiteit Groningen
Begeleider(s)/adviseur	van Wees, Bart, Supervisor Vera Marun, Ivan, Co-supervisor Roche, Stephan, Beoordelingscommissie, Externe Persoon Esquinazi, Pablo, Beoordelingscommissie, Externe Persoon Ye, Justin, Beoordelingscommissie
Datum van toekenning	8-sep.-2014
Plaats van publicatie	[S.l.]
Uitgever	[S.n.]
Gedrukte ISBN's	978-90-367-7196-2
Elektronische ISBN's	978-90-367-7195-5
Status	Published - 2014

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title = "Exploring magnetism in graphene by electronic charge and spin transport",

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.",

author = "Magdalena Wojtaszek",

year = "2014",

language = "English",

isbn = "978-90-367-7196-2",

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AU - Wojtaszek, Magdalena

PY - 2014

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N2 - 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.

AB - 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.

M3 - Thesis fully internal (DIV)

SN - 978-90-367-7196-2

PB - [S.n.]

CY - [S.l.]

ER -

Exploring magnetism in graphene by electronic charge and spin transport

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