RNDr. Stanislav Kamba, CSc., DSc.
We focus on the study of dielectric and vibration spectra of ferroelectrics and multiferroics in the form of single crystals, ceramics, composites, thin films and multilayers in a very broad spectral and temperature range (1 mHz – 150 THz, 5 – 950 K). Using these techniques, we investigate dynamics of ferroelectric phase transitions, i.e. optical soft modes driving displacive phase transitions and anomalous dielectric relaxations causing huge dielectric dispersion near the order-disorder ferroelectric phase transitions or in the relaxor ferroelectrics. Broad-band dielectric or conductivity spectra allow us to explain also origin of the giant dielectric permittivity in various composites or materials with inhomogeneous conductivity (e.g. in ceramic grains and their grain boundaries). Also, we can measure ferroelectric polarization in the broad temperature range.
Magnetic field dependence of dielectric permittivity and ferroelectric polarization can be measured in external magnetic fields up to 19 Tesla. For these experiments we use several magnets and PPMS in joint lab of FZU and MFF UK. Our new microwave network wave analyzer is able to measure magnetic resonances up 3 GHz (100 – 400 K), in preparation is a setup for studies of the magnetic resonances up to 50 GHz (without external magnetic field) at temperatures down to 10 K. It will allow us to study dynamics of magnetic phase transitions. In collaboration with the Terahertz group we also study influence of the external magnetic fields (up to 7 T) on magnons and electromagnons for understanding the dynamic magnetoelectric coupling in various multiferroics.
