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Graphene as a Reversible Spin Manipulator of Molecular Magnets
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2011 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 107, no 25, 257202- p.Article in journal (Refereed) Published
Abstract [en]

One of the primary objectives in molecular nanospintronics is to manipulate the spin states of organic molecules with a d-electron center, by suitable external means. In this Letter, we demonstrate by first principles density functional calculations, as well as second order perturbation theory, that a strain induced change of the spin state, from S = 1 -> S = 2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in the sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation. The effect is brought about by a change in Fe-N bond length in FeP, which influences the molecular level diagram as well as the interaction between the C atoms of the graphene layer and the molecular orbitals of FeP.

Place, publisher, year, edition, pages
2011. Vol. 107, no 25, 257202- p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-167201DOI: 10.1103/PhysRevLett.107.257202ISI: 000298133000003OAI: oai:DiVA.org:uu-167201DiVA: diva2:481881
Available from: 2012-01-23 Created: 2012-01-23 Last updated: 2014-04-29Bibliographically approved
In thesis
1. First Principles Studies of Functional Materials Based on Graphene and Organometallics
Open this publication in new window or tab >>First Principles Studies of Functional Materials Based on Graphene and Organometallics
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Graphene is foreseen to be the basis of future electronics owing to its ultra thin structure, extremely high charge carrier mobility,  high thermal conductivity etc., which are expected to overcome the size limitation and heat dissipation problem in silicon based transistors. But these great prospects are hindered by the metallic nature of pristine graphene even at charge neutrality point, which allows to flow current even when a transistor is switched off. A part  of the thesis is dedicated to invoke electronic band gaps in graphene to overcome this problem. The concept of quantum confinement has been employed to tune the band gaps in graphene by  dimensional confinement along with the functionalization of the edges of these confined nanostructures. Thermodynamic stability of the functionalized zigzag edges with hydrogen, fluorine and reconstructed edges has been presented in the thesis. Keeping an eye towards the same goal of band gap opening,  a different route has been considered by admixing insulating hexagonal boron nitride (h-BN) with semimetal graphene. The idea has been implemented in two  dimensional h-BN-graphene composites and three dimensional stacked heterostructures. The study reveals the possibility of tuning band gaps by controlling the admixture. Occurrence of defects in graphene has significant effect on its electronic properties. By random insertion of defects, amorphous graphene is studied, revealing a semi-metal to a metal transition.

The field of molecular electronics and spintronics aims towards device realization at the molecular scale. In this thesis, different aspects of magnetic bistability in organometallic molecules have been explored in order to design  practical spintronics devices. Manipulation of spin states in organometallic molecules, specifically metal porphyrin molecules, is achieved by controlling surface–molecule interaction. It has been shown that by strain engineering in defected graphene, the magnetic state of adsorbed molecules can be changed. The spin crossover between different spin states can also be achieved by chemisorption on magnetic surfaces. A significant part of the thesis demonstrates that the surface-molecule interaction not only changes the spin state of the molecule, but allows to manipulate magnetic anisotropies and spin dipole moments via modified ligand fields. Finally, in collaboration with experimentalists, a practical realization of switching surface–molecule magnetic interactions by external magnetic fields is demonstrated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 90 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1120
Graphene, Magnetism, Organometallics, Density functional theory, Electron correlation, Spin switching, Nanoribbons, Exchange interaction, Edge functionalization, Band gap
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
urn:nbn:se:uu:diva-217175 (URN)978-91-554-8869-7 (ISBN)
Public defence
2014-03-14, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Available from: 2014-02-21 Created: 2014-01-30 Last updated: 2014-04-29

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