Giant magnetoelectric effect in new multiferroics

Rapid development of modern electronics requires a continuous search for new mechanisms of controlling the electric and magnetic properties of materials. One of the promising recent developments targets materials with the magnetoelectric effect which allow to modify electric properties by magnetic field and magnetization by electric voltage. In view of future application, the absolute value of the magnetoelectric coupling and the understanding of the underlying mechanisms of the magnetoelectricity are of crucial importance. One newly discovered material class with giant magnetoelectric coupling is provided by rare-earth borates promising record values of the magnetoelectric effect. This material class is especially intriguing as static and dynamic properties seem to be governed by the same mechanism. In the present project using a combination of spectroscopy, neutron scattering and various theoretical approaches we intend to provide an understanding of the magnetoelectricity in borates. Comparing high quality crystals with varying composition we aim to separate different contributions to the microscopic mechanism of the magnetoelectricity and to optimize the magnetoelectric coupling in this material class.

Rapid development of modern electronics requires a continuous search for new mechanisms of controlling electric and magnetic properties of materials. One of the promising recent developments targets materials with the magnetoelectric effect which allow to modify electric properties by magnetic field and magnetization by electric voltage. In view of future application, the absolute value of the magnetoelectric coupling and the understanding of the underlying mechanisms of the magnetoelectricity are of crucial importance. One newly discovered material class with giant magnetoelectric coupling is provided by rare- earth borates promising record values of the magnetoelectric effect. This material class is especially intriguing as static and dynamic properties seem to be governed by the same mechanism. In the present project using a combination of spectroscopy, static experiments and theory, we provided an understanding of the mechanism of the dynamic magnetoelectric effect in borates. Within this project we demonstrated several unusual optical effects in multiferroic borates. One such effect is the asymmetric transmission, i.e. the material is transparent for the light propagating in one direction, but opaque for the opposite direction. This counter-intuitive effect can be explained via strong magnetoelectric coupling in borates. In a subsequent experiment we proved that in a magnetoelectric material the measured optical activity can show another unusual effect of being reversed under both fundamental symmetry operations, time and space inversions. This work completes the experimental symmetry table of possible light-matter interactions.