Femtosecond dynamics of the collinear-to-spiral antiferromagnetic phase transition in CuO

TL;DR

This study investigates the ultrafast femtosecond-scale transition from collinear to spiral antiferromagnetic phases in CuO triggered by optical excitation, revealing the speed limit set by magnetic excitations.

Contribution

It demonstrates the real-time dynamics of magnetic phase transition in CuO using femtosecond x-ray diffraction, highlighting the transition speed limit due to magnetic excitations.

Findings

Transition occurs within 400 fs to 2 ps after excitation.

Magnetic order shifts from collinear to spiral phase.

Transition speed limited by magnetic excitations.

Abstract

We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic re-orientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.