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Exotic magnetic phenomena in transition metal materials

18 December 2009

Promotie: T.T.A. Lummen, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen
Proefschrift: Exotic magnetic phenomena in transition metal materials
Promotor(s): prof.dr. P.H.M. van Loosdrecht
Faculteit: Wiskunde en Natuurwetenschappen
Contact: Tom Lummen, tel. 050-363 4352, e-mail:

Exotic magnetic phenomena in transition metal materials

Even today, magnetism remains one of the fundamental areas of interest within the materials science community. This is because revolutionairy new effects related to the magnetic interactions in materialen are still being discovered. The mutual couplings between microscopic lattice, spin, orbital and charge degrees of freedom in materials result in a complex equilibrium that, in special cases, can lead to fascinating new phenomena such as the recently discovered giant magnetoresistance and high-temperature superconductivity. The research described in this thesis focuses on a number of these special cases, in which the magnetism of the studied materials exhibits unusual behaviour. In general, two classes of materials are discussed, in which optically-controllable magnetism and geometrically frustrated magnetism are investigated, respectively.

In the first chapters, the spotlight is on one of the so-called Prussian Blue Analogues, in which an internal redox reaction can be induced through both temperature and light, thereby drastically changing its magnetism. Because these fascinating transition phenomena were found to be accompanied by cooperative interactions between the involved magnetic units, it was proven to be possible to switch the macroscopic magnetism in the material at low temperature using visible light.

The later chapters focus on a number materials whose specific structure prevents the satisfaction of their primary magnetic interactions; geometrically frustrated materials. Because of this precarious situation, it are the secondary interactions in the material that dominate the (unusual) magnetic behavior; the crystal field splitting and the spin-lattice coupling were shown to be dominant in the respective studied systems.

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