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Emergent Spin Ordering at C60 interfaces

Al Ma’Mari, Fatma Ali Salim (2016) Emergent Spin Ordering at C60 interfaces. PhD thesis, University of Leeds.

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Abstract

This work is a pioneer study on the role played by molecular interfaces in altering the electronic states of non-ferromagnetic materials. Here, we consider diamagnetic copper and paramagnetic manganese and scandium, to overcome the Stoner criterion and make them magnetically ordered at room temperature. The mechanism is mediated by the charge transfer from the transition metal and hybridization with molecular carbon, creating new 3d-π that drastically modify the electron energy bands around the Fermi energy of both metal and molecule. This effect is achieved via interfaces between metallic thin films and C60 molecular layers. The emergent spin ordering arising in these systems is measured using magnetometry shows magnetically ordered behaviour at room temperature, but dependent on the thickness and continuity of the metallic layer. To determine how in the layered structure the emergent spin ordering is distributed, low-energy muon spin spectroscopy is utilised by studying the depolarization process of low-energy muons implanted in the sample. This technique indicates localised spin-ordered states at, and close to, the metallo-molecular interface. X-ray absorption spectroscopy provides an excellent tool for identifying the emergent spin ordering of specific elements within a sample. The change in the molecular orbitals of C60 due to charge transfer and 3d-π hybridization is evaluated based on this technique. The presence of spin ordering in a non-magnetic metallic host due to molecular charge transfer has a drastic effect not only on the magnetic but also on the transport properties of the system. The decisive role of the molecular interfaces in the physics of spin dependent scattering within a non-magnetic host has been demonstrated. Localised spin ordering leads to changes in the Kondo and weak localisation effects with applications in low temperature thermometry and quantum devices. It is found that there is an additional magnetic scattering that has a pronounced contribution when C60 molecules are embedded into the non-magnetic Cu and hence creates localised spins. The localised spin ordering that emerged at molecular interfaces is a new approach for novel generation of materials for future spintronics devices.

Item Type: Thesis (PhD)
Keywords: Molecular interfaces, Stoner criterion, Charge transfer, Magnetism, Molecular carbon, Emergent spin ordering, C60 fullerene
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds)
Identification Number/EthosID: uk.bl.ethos.695956
Depositing User: MISS FATMA ALI SALIM AL MA’MARI
Date Deposited: 16 Nov 2016 11:34
Last Modified: 18 Feb 2020 12:31
URI: http://etheses.whiterose.ac.uk/id/eprint/15256

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