Speaker
Dr
Sonja Holm
(Aarhus University)
Description
Unconventional ground states and excitations in low dimensional, frustrated, magnetic materials is currently a hot topic in experimental condensed matter physics. The frustrated antiferromagnetic system YMnO3 known to be both a frustrated 2D XY system and a multiferroic material falls within this field. As the system is multiferroic there is a strong coupling between the magnetic moments and the ion positions, and therefore also between the magnetic excitations and the phonon modes. At the conference, we will present inelastic neutron scattering data and theoretical calculations of the magneto-elastic excitations in h-YMnO3. Experimentally, an avoided crossing is found between magnon and phonon modes close to the boundary of the Brillouin zone. This is further confirmed by neutron polarization analysis. The theoretical model including Heisenberg spins and a magneto-elastic coupling to the acoustic phonon modes via the single-ion magnetostriction reproduces the dispersion and intensities of all modes in the full Brillouin zone, describes the observed magnon-phonon hybridized modes, and quantifies the magneto-elastic coupling. An external magnetic field along the c-axis is observed to cause a linear field-induced splitting of one spin wave branch, also reproduced by the model. The combined information, including the splitting and the two dispersions, allows us to exclude several of the earlier proposed magnetic ground states and dynamic models for this system.
Primary author
Dr
Sonja Holm
(Aarhus University)
