Probing ultrafast spin dynamics in the antiferromagnetic multiferroic HoMnO$_3$ through a magnon resonance

TL;DR

This paper introduces a novel method to directly measure ultrafast energy transfer between electrons and magnons in antiferromagnetic HoMnO3, revealing faster spin-lattice thermalization compared to ferromagnetic systems.

Contribution

It presents a new optical and THz spectroscopy technique to track spin dynamics and provides a Boltzmann model for understanding spin-lattice thermalization in antiferromagnets.

Findings

Photoinduced transparency builds up over several picoseconds.

Spin-lattice thermalization in AFMs is ~10 times faster than in FMs.

A Boltzmann equation model explains differences in thermalization processes.

Abstract

We demonstrate a new approach for directly measuring the ultrafast energy transfer between elec- trons and magnons, enabling us to track spin dynamics in an antiferromagnet (AFM). In multiferroic HoMnO3, optical photoexcitation creates hot electrons, after which changes in the spin order are probed with a THz pulse tuned to a magnon resonance. This reveals a photoinduced transparency, which builds up over several picoseconds as the spins heat up due to energy transfer from hot elec- trons via phonons. This spin-lattice thermalization time is ?10 times faster than that of typical ferromagnetic (FM) manganites. We qualitatively explain the fundamental differences in spin-lattice thermalization between FM and AFM systems and apply a Boltzmann equation model for treating AFMs. Our work gives new insight into spin-lattice thermalization in AFMs and demonstrates a new approach for directly monitoring the ultrafast dynamics of spin order in these systems.