Laser-induced THz magnetism of antiferromagnetic CoF$_2$

TL;DR

This study demonstrates the excitation and detection of THz-frequency magnetic oscillations in antiferromagnetic CoF$_2$ using sub-10 fs laser pulses, revealing coherent phonon and magnon modes through time-resolved polarimetry.

Contribution

It provides experimental evidence of laser-induced THz magnetic dynamics in an antiferromagnet, linking phonon and magnon excitations to magnetic birefringence oscillations.

Findings

Detection of 7.45 THz circular birefringence oscillations below Néel temperature.

Observation of 3.4 THz two-magnon mode oscillations.

Identification of the symmetry of the two-magnon mode through polarization analysis.

Abstract

Excitation, detection and control of coherent THz magnetic excitation in antiferromagnets are challenging problems that can be addressed using ever shorter laser pulses. We study experimentally excitation of magnetic dynamics at THz frequencies in an antiferromagnetic insulator CoF$_2$ by sub-10 fs laser pulses. Time-resolved pump-probe polarimetric measurements at different temperatures and probe polarizations reveal laser-induced transient circular birefringence oscillating at the frequency of 7.45 THz and present below the N\'eel temperature. The THz oscillations of circular birefringence are ascribed to oscillations of the magnetic moments of Co$^{2+}$ ions induced by the laser-driven coherent E$_g$ phonon mode via the THz analogue of the transverse piezomagnetic effect. It is also shown that the same pulse launches coherent oscillations of the magnetic linear birefringence at the frequency of 3.4 THz corresponding to the two-magnon mode. Analysis of the probe polarization dependence of the transient magnetic linear birefringence at the frequency of the two-magnon mode enables identifying its symmetry.