Speaker: Elisabeth Bothschafter, Paul Scherrer Institute
Program Description
Multiferroic materials exhibit intriguing possibilities to study ferroelectric and ferromagnetic ordering phenomena in solids due to strong electron-electron correlations and electron-lattice coupling. For potential technological applications, e.g. in sensors and data storage, the control of both magnetic and electric properties at the picosecond time-scale using short light pulses is of great interest.
Multiferroic TbMnO3 exhibits strong magneto-electric coupling and it has been shown that its magnetic order can be influenced by the electric field of an intense THz pulse thanks to an electro-magnon resonance [1]. In order to investigate the effect of optical excitation on the magnetic order in TbMnO3, we conducted time-resolved near-infrared-pump X-ray-probe experiments. Polarization resolved resonant scattering of a [0 1 0] oriented crystal allows to observe the magnetic order. Below TN=42 K it is antiferromagnetic and incommensurate with a temperature dependent propagation vector q of the sinusoidal spin-density wave along the b-axis. Below a temperature Tlock= 28 K the material develops a cycloidal spin order which breaks the inversion symmetry of the unit cell, resulting in a ferroelectric moment [2].
Our results show that the melting of long-range order is on the timescale of several tens of picoseconds [3]. We find that the cycloidal order is destroyed faster than the spin-density wave contribution to the magnetic order which indicates that the material passes through a transient magnetic phase during the melting of long-range magnetic order.
1. T. Kubacka et al., Science 343, 1333 (2014).
2. M. Kenzelmann et al. Phys. Rev. Lett. 95, 87206 (2005).
3. J.A. Johnson et al., Phys. Rev. B (accepted), arXiv:1507.06628 .
