Colloquium
Department of Physics, NCU
Photo-creating supercooled spiral-spin states in a multiferroic manganite
Speaker
Prof. Yu-Miin Sheu (許鈺敏)
NCTU Electrophysics
Date 2016.11.08(Tue)
Time 14:00
Place S4-625
Multiferroic manganites possess ferroelectric order of spiral-spin origin. The two spin states, ab- and bc-spiral, result in the ferroelectric order along the crystal a or c axis respectively. [1] In this seminar, I will demonstrate that dynamics of the ab-spiral-spin order in a magnetoelectric multiferroic Eu0.55Y0.45MnO3 (EYMO) can be unambiguously probed through optical second harmonic signal, generated via the spin-induced ferroelectric polarization. In case of relatively weak photoexcitation, the ferroelectric and spiral-spin orders remain interlocked while relaxing through spin-lattice relaxation in the non-equilibrium state. When the additional optical pulse illuminating sample is intense enough to induced local phase transition thermally, the system creates a metastable state of bc-spiral-spin order (with electric polarization P//c) via supercooling across the first-order phase transition between the ab- and bc-spiral. The supercooled state of bc-spiral spin is formed in thermodynamical ground state of the ab-spiral (P//a), displaying a prolonged lifetime, in particular under its favorable magnetic field along the a-axis. [1] The observed photo-switching between the two distinct multiferroic states sheds light on novel photoinduced phenomena in spiral-spin multiferroics.
1. H. Murakawa et al., Phys. Rev. Lett. 101, 197207 (2008).