Dynamic pathway of the photoinduced magnetic phase transition of multiferroic TbMnO3

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 .