The field of single-molecule magnetism studies nanoscopic objects which exhibit superparamagnetic behavior below a certain temperature. The molecular magnet consists of one or several magnetic metal ions and the surrounding ligands that form the desired environment. Manganese was the first from 3d metals to show a delayed relaxation of magnetization and magnetic hysteresis in Mn12AC molecule in 1993. Later 4f elements were found to be even better candidates for single-molecule magnets.
Endohedral fullerenes show a wide potential in encapsulating 4f elements. Not only fullerenes with one or several 4f-block metal ions can be obtained but also various clusterfullerenes comprising several positively charged metal ions and up to several negatively charged ions like N-3, S-2, etc. Importantly not only 4f elements can form clusters inside the fullerene cage but also non-magnetic metals like Y and Sc. This allows to vary the number of magnetic ion in the cluster retaining almost similar structure.
This thesis reports magnetic studies of various Dy endohedral fullerenes:
DySc2N@C80 and Dy2ScN@C80, which are the pioneer endohedral fullerene single-molecule magnets. For DySc2N@C80, the intriguing process of quantum tunneling of magnetization was studied in detail for powder and single-crystal samples with different dilution methods. For Dy2ScN@C80, the coupling between two Dy ion is of the main interest. Magnetic studies of this compound revealed: that the quantum tunneling process is effectively suppressed due to exchange interactions in the cluster; and a large anisotropy barrier of 1735±21 K.
Dy2S@C82-Cs, -C3v, Dy2S@C72-Cs, Dy2C2@C82-Cs fullerenes were studied in order to obtain a deeper understanding of the coupling of magnetic elements inside the cage. The investigation of a fullerene family with a similar cluster in cages of different symmetry and different clusters in the same fullerene cage allowed to separate the influence of the cluster composition and the cage structure on magnetic properties of endohedral metallofullerene single-molecule magnets. The cage structure was found to have a dominant influence.
Dy2@C80(CH2Ph) is a special endohedral metallofullerene with a single-electron Dy Dy bond. It represents the ultimate case of magnetic coupling and exhibits a record-high blocking temperature (21.9 K) among di-metal single-molecule magnets.
The comparison of obtained results allowed to understand how the quantum tunneling is influenced by of both intramolecular interactions and magnetic coupling inside the fullerene cage. Also, Dy2@C80(CH2Ph) endohedral metallofullerene with a single-electron lanthanide-lanthanide bond opens the new class of tunable single-molecule magnets, with outstanding magnetic properties.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:31125 |
| Date | 30 August 2018 |
| Creators | Krylov, Denis |
| Contributors | Popov, Alexey, Büchner, Bernd, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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