Crucial role of spin-lattice relaxation in gigantic switchable optomagnet effect of (Fe_1-yZn_y)₂Mo₃O₈

Yao Hua Zhuang^1*, Y. M. Chang¹, C. P. Chang¹, T. Kurumaji², Y. Tokura^3,4, Y. M. Sheu^1,5

¹Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan
²Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
³RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
⁴Department of Applied Physics and Tokyo College, University of Tokyo, Tokyo 113-8656, Japan
⁵Center for Emergent Functional Matter Science, National Chiao Tung University, Hsinchu 30010, Taiwan

* Presenter:Yao Hua Zhuang, email:jack94319579@gmail.com

(Fe_1-yZn_y)₂Mo₃O₈ (FZMO) family is magnetoelectric multiferroics where gigantic and switchable optomagnet effect occurs in antiferromagnetic phase that compete with ferrimagnetic phase. The optomagnet effect do not need spin canting or spin-orbit coupling as a prerequisite. However, spin-lattice relaxation does play a role to assist the large enhancement of magnetization reversal after the light pulse disappears after 200 fs. Using time-resolved magnetic birefringent effect (TR-MBE) and second harmonic generation (TR-SHG) technique, we selectively probe magnetic order and ferroelectric order of (100) FZMOs. In this geometry, we avoid the optomagnet effect and we study the change in magnetic and ferroelectric order due to laser induced heating. We find that both magnetic and ferroelectric order strongly coupled to each other at any timescale, despite that we directly excite magnetic resonance. Moreover, we reveal that spin-lattice coupling brings effective spin and ferroelectric temperature to equilibrate with lattice on a timescale of hundreds of picoseconds, which is consistent with the timescale observed in FZMO with y = 0.125 where gigantic optomagnet effect occurs. Our study unveils that the spin-lattice coupling time, rather than the flipped spin lifetime, plays important role on the novel gigantic enhancement of optomagnet effect in FZMO.

Keywords: optomagnet effect, spin-lattice relaxation, time-resolved, birefringence, second harmonic generation