Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3

TL;DR

This study investigates ultrafast laser-induced melting of magnetic order in multiferroic TbMnO3, revealing a slow decay process and unique spin dynamics influenced by low magnon velocities.

Contribution

It provides new insights into the non-equilibrium spin dynamics and melting process of magnetic order in TbMnO3 using ultrafast spectroscopy and proposes a model explaining the slow decay.

Findings

Magnetic order melts with a decay time of ~22 ps.

No change in spin wavevector despite increased effective temperature.

Slow magnon group velocity hinders wavevector change.

Abstract

We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously observed in other systems. To explain the data we propose a simple model of the melting process where the pump laser pulse directly excites the electronic system, which then leads to an increase in the effective temperature of the spin system via a slower relaxation mechanism. Despite this apparent increase in the effective spin temperature, we do not observe changes in the wavevector q of the antiferromagnetic spin order that would typically correlate with an increase in temperature under equilibrium conditions. We suggest that this behavior results from the extremely low magnon group velocity that hinders a change in the spin-spiral wavevector on these time scales.