Phonons, electromagnons and magnetic ordering

Multiferroics represent one of the hot topics in the fundamental research of the multifunctional materials. In multiferroics the ferroelectric polarization and (anti-)ferromagnetic ordering closely coexist and may strongly interact. The research interests of both applicants are focused on elementary excitations in this class of materials. One of the main topics is given by lattice excitations (phonons) which are coupled to the spin waves and are called electromagnons. The goal of the present project is the systematic investigation of two types of correlation effects: (i) the renormalization of the lattice vibrations at the onset of a magnetic order (spin-phonon coupling) and (ii) the correlation between phonons and electromagnons (electromagnon-phonon-coupling). In order to obtain a full picture of the relevant elementary excitations and their correlations in multiferroic phases these effects will be studied using different material systems: firstly, in a classical multiferroic system of pure and isoelectronically doped rare earth manganites RMnO 3 (R = Eu, Gd, Tb, and Eu1-x Yx ) and, secondly, in a new multiferroic system ACrO 2 (A = Cu, Ag, Li, Na). The investigations will be done using the combination of the Raman spectroscopy with the optical spectroscopy in the far infrared and terahertz ranges, both at low temperatures and in external magnetic fields.

Multiferroics represent one of the hot topics in the fundamental research of the multi-functional materials. In multiferroics the ferroelectric polarization and (anti-)ferromagnetic ordering closely coexist and may strongly interact. The research interests of both applicants are focused on elementary excitations in this class of materials. One of the main topics is given by lattice excitations (phonons) which are coupled to the spin waves and are called electromagnons. The goal of the present project is the systematic investigation of two types of correlation effects: (i) the renormalization of the lattice vibrations at the onset of a magnetic order (spin-phonon coupling) and (ii) the correlation between phonons and electromagnons (electromagnon- phonon-coupling). In order to obtain a full picture of the relevant elementary excitations and their correlations in multiferroic phases these effects will be studied using different material systems: firstly, in a classical multiferroic system of pure and isoelectronically doped rare earth manganites RMnO3 (R = Eu, Gd, Tb, and Eu1-xYx) and, secondly, in a new multiferroic system ACrO2 (A = Cu, Ag, Li, Na). The investigations will be done using the combination of the Raman spectroscopy with the optical spectroscopy in the far infrared and terahertz ranges, both at low temperatures and in external magnetic fields.