Graphite is the strongest diamagnet of all known materials to date. Recent studies of the thickness dependence of the resistance of graphite have demonstrated the heterogeneity of the charge distribution in bulk graphite and prompted the study of its magnetic properties. The studies of the thickness dependence of the magnetic susceptibility of graphite, done in this work, showed that two-dimensional interfaces between the crystalline (Bernal or rhombohedral stacking order) blocks in graphite make a dominant contribution to its diamagnetic susceptibility. Previously proposed models of diamagnetism in graphite are not suitable for explaining its magnetic properties, and therefore new concepts should be considered. Additionally, the studies of the transport and magnetic properties of graphite and multilayer graphene indicated the existence of superconductivity at the interfaces in well-ordered graphite. The possibility of creating permanent circulating currents around artificial holes
in highly oriented graphite was studied by highly sensitive magnetization measurements. The obtained results provide hints for the possible existence of superconducting regions inside the bulk highly ordered graphite.
In the present thesis, a further thickness dependent phenomenon on the depinning line (DL) of the flux line lattice of the high-Tc superconductor Bi2Sr2CaCu2O8+δ was studied. This geometrical effect shifts to notably lower temperatures in micrometer ring, compared with bulk crystals and thin flakes.
The shift is related to a decrease in the overall pinning potential as a result of size effects, caused by: a) the thickness of the sample being smaller than the pinning correlation length, and b) the increase in the effective London penetration depth of the vortices (Pearl vortices). The large shift of the DL to
lower temperatures may significantly influence the suitability of such elements for device applications in microstrip antennas and THz emitters.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:73036 |
| Date | 04 December 2020 |
| Creators | Semenenko, Bogdan |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/acceptedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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