X-ray magnetic circular dichroism (XMCD) of metallic nano-structures on epitaxial graphene

dc.contributor.advisor David Vaknin
dc.contributor.author Anderson, Nathaniel
dc.contributor.department Physics and Astronomy
dc.date 2021-06-11T00:46:12.000
dc.date.accessioned 2021-08-14T06:32:20Z
dc.date.available 2021-08-14T06:32:20Z
dc.date.copyright Sat May 01 00:00:00 UTC 2021
dc.date.embargo 2021-04-16
dc.date.issued 2021-01-01
dc.description.abstract <p>X-ray magnetic circular dichroism (XMCD) reveals the properties of intercalated Eu/Dy/Gd and Fe/Dy islands on top of graphene on SiC(0001). Intercalated nano-clusters of Eu/Dy/Gd are formed by deposition on epitaxially grown graphene then annealment at high temperatures. STM images reveal that the graphene surface is defect free and that Eu/Dy/Gd have distinct nucleation patterns, with Eu forming distinct clusters on the Moir{\'e} pattern, while Dy and Gd are randomly distributed. XMCD measurements show the metals have a paramagnetic-like behavior with moments lower than predicted by the Brillouin function and that the intercalants are passivated beneath the graphene and stable under atmospheric exposure for months.</p> <p>Fe and Dy nano-islands are grown on top of graphene then capped with Au for passivation. From XMCD, field and temperature dependence of the magnetic moment of Dy show paramagnetic behavior. The magnetic moment is not saturated at $H = 5$ T even at temperatures below which bulk-Dy is ferromagnetic. For the Fe, XMCD reveals that the gold was insufficient at capping and allowed for oxidation and spontaneous formation of magnetite nano-particles \ce{Fe3O4}. XMCD spectra show a thin sample fully oxidized and a thicker sample as part \ce{Fe3O4} and part metallic Fe. Field dependence shows a hysteresis similar to that of magnetite and temperature shows evidence of the Verwey transition at T = 125 K.</p> <p>The magnetic properties for the combination of Fe islands and intercalated Gd is explored. Gold capping of the Fe was successful for a thin sample, but failed to prevent oxidation of the thicker sample. Field dependence XMCD of the Fe shows saturation at $H = 0.5$ T with values of $\sim$0.31$\mu_B$ and $\sim$0.16$\mu_B$ for the thin and thick samples, respectively. The oxidized thicker sample shows anisotropy with the respect to the incident angle while the metallic thinner sample has no anisotropy. For Gd, the two samples show nearly identical linear behavior with moments well below those of the Brillouin function.</p> <p>The inverse spinel \ce{Co2VO4} is also investigated with XMCD. At 75K, the magnetic moment of the spinel flips directions; however, with XMCD we show that the octahedral \ce{V^{4+}} and tetrahedral \ce{Co^{2+}} flip while the octahedral \ce{Co^{2+}} remains unchanged.</p>
dc.format.mimetype application/pdf
dc.identifier archive/lib.dr.iastate.edu/etd/18445/
dc.identifier.articleid 9452
dc.identifier.contextkey 23293775
dc.identifier.doi https://doi.org/10.31274/etd-20210609-6
dc.identifier.s3bucket isulib-bepress-aws-west
dc.identifier.submissionpath etd/18445
dc.identifier.uri https://dr.lib.iastate.edu/handle/20.500.12876/7rKoNAQr
dc.language.iso en
dc.source.bitstream archive/lib.dr.iastate.edu/etd/18445/Anderson_iastate_0097E_19461.pdf|||Fri Jan 14 21:42:08 UTC 2022
dc.subject.keywords Graphene
dc.subject.keywords Intercalation
dc.subject.keywords Nano-islands
dc.subject.keywords XMCD
dc.title X-ray magnetic circular dichroism (XMCD) of metallic nano-structures on epitaxial graphene
dc.type article
dc.type.genre dissertation
dspace.entity.type Publication
relation.isOrgUnitOfPublication 4a05cd4d-8749-4cff-96b1-32eca381d930
thesis.degree.discipline Condensed Matter Physics
thesis.degree.level dissertation
thesis.degree.name Doctor of Philosophy
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