Revealing magnetoelectric coupling effect in polar antiferromagnet Fe$_2$Mo$_3$O$_8$ by static and time resolved second harmonic generation

TL;DR

This study uses static and time-resolved second harmonic generation to investigate the magnetoelectric coupling and ultrafast phase transitions in the polar antiferromagnet Fe$_2$Mo$_3$O$_8$, revealing a magnetic order-induced polarization change and photoinduced phase transition.

Contribution

It demonstrates the first combined static and ultrafast SHG analysis of magnetoelectric coupling in Fe$_2$Mo$_3$O$_8$, showing ultrafast polarization dynamics and phase transition behavior.

Findings

Only $ ext{χ}_{ccc}^{(2)}$ changes below $T_N$, indicating polarization coupling.

Ultrafast laser pulses induce a rapid transition from AFM to paramagnetic state.

Evidence of a photoinduced ultrafast phase transition in Fe$_2$Mo$_3$O$_8$.

Abstract

We present both static and time-resolved second harmonic generation (SHG) measurements on polar antiferromagnet Fe$_2$Mo$_3$O$_8$ to monitor the evolution of the electric polarization change and its coupling to magnetic order. We find that only one of the second order tensor elements, $\chi_{ccc}^{(2)}$ ,shows a prominent change below the Neel temperature $T_N = 60$ K, indicating a magnetic order induced electric polarization change along the c-axis. Time-resolved SHG measurement reveals an ultrafast recovery of the second order tensor element upon the ultrashort laser excitation with fluence above 0.3 $mJ/cm^2$, yielding evidence for a photoinduced ultrafast phase transition from the AFM ordered state to the paramagnetic state. Our work will help understand the spin induced polarization and the ultrafast optical tuning effect in Fe$_{2}$Mo$_{3}$O$_{8}$.