Nanoscale transient magnetization gratings excited and probed by femtosecond extreme ultraviolet pulses

TL;DR

This paper demonstrates the generation and probing of nanoscale transient magnetization gratings using femtosecond EUV pulses from a free electron laser, enabling ultrafast magnetic dynamics studies at nanometer scales.

Contribution

It introduces a novel method combining EUV pulses and resonant probing to create and analyze transient magnetic and electronic gratings at nanometer resolution.

Findings

Electronic excitation with 50 fs rise time and 0.5 ps decay in demagnetized samples.

Observation of sub-picosecond magnetization grating formation.

Magnetization decay over tens of picoseconds due to thermal diffusion.

Abstract

We utilize coherent femtosecond extreme ultraviolet (EUV) pulses derived from a free electron laser (FEL) to generate transient periodic magnetization patterns with periods as short as 44 nm. Combining spatially periodic excitation with resonant probing at the dichroic M-edge of cobalt allows us to create and probe transient gratings of electronic and magnetic excitations in a CoGd alloy. In a demagnetized sample, we observe an electronic excitation with 50 fs rise time close to the FEL pulse duration and ~0.5 ps decay time within the range for the electron-phonon relaxation in metals. When the experiment is performed on a sample magnetized to saturation in an external field, we observe a magnetization grating, which appears on a sub-picosecond time scale as the sample is demagnetized at the maxima of the EUV intensity and then decays on the time scale of tens of picoseconds via thermal diffusion. The described approach opens prospects for studying dynamics of ultrafast magnetic phenomena on nanometer length scales.