Frustrated Magnets

Due to their complex structure, geometrically frustrated magnets can not satisfy all magnetic exchange interactions between their spins concommitantly. A simple example is the triangular arrangement of Ising-spins (left), in which antiferromagnetic exchange yields spin frustration. Geometrically frustration hence competes with spin ordering, thereby suppressing ordered phases and giving rise to novel phenomena such as macroscopic degeneracy of the ground state, quantum criticallity and anomalous energy scales. E.g., in structurally disordered magnets one often observes a spin-glas, whereas, in structurally ordered but geometrically frustated systems spin-liquid or spin-ice phases are realized. Another realisation of a geometrically frustrated magnet are CuO₂ spin chains (sketched right) in which the ferromagnetic nearest neighbor ecxchange competes with antiferromagnetic next nearest neighbor interactions. In this case, a quantum critical point appears for a certain frustration ratio of nearest to next nearest neigbor coupling, which generates peculiar properties of compounds with similar frustation ratio.

Investigation of geometrically frustrated magnets is not only valuable for basic research, but there are also very promising perspectives for technologically innovative applications. One example are novel magnetic refrigerators, multiferroics or ultrafast optical devices. Both the potential applications and the spectacular physical effects give rise to an increasing international interest on this topic.

We are working on the following geometrically frustrated systems:

• Spinel systems
• Spin chain systems (Li₂CuO₂, Li₂ZrCuO₄, (Sr,La,Ca)₁₄Cu₂₄O₄₁, LiVCuO₄, etc.)

For further information please contact: Dr. Anja Wolter