Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction

TL;DR

This study combines ultrafast X-ray diffraction and magneto-optical measurements to track picosecond strain pulses in heterostructures with giant magnetostriction, revealing detailed strain dynamics and their magnetic effects.

Contribution

It introduces a background-free method to characterize laser-generated strain pulses in heterostructures using combined UXRD and MOKE techniques, with predictive modeling of strain reflections.

Findings

Symmetric bipolar strain pulses observed in uncoated samples.

Asymmetric bipolar and unipolar pulses in capped samples.

Linear MOKE response to strain amplitude due to inverse magnetostriction.

Abstract

We combine ultrafast X-ray diffraction (UXRD) and time-resolved Magneto-Optical Kerr Effect (MOKE) measurements to monitor the strain pulses in laser-excited TbFe2/Nb heterostructures. Spatial separation of the Nb detection layer from the laser excitation region allows for a background free characterization of the laser-generated strain pulses. We clearly observe symmetric bipolar strain pulses when the excited TbFe2 surface terminates the sample and a decomposition of the strain wavepacket into an asymmetric bipolar and a unipolar pulse, when a SiO2 glass capping layer covers the excited TbFe2 layer. The inverse magnetostriction of the temporally separated unipolar strain pulses in this sample leads to a MOKE signal that linearly depends on the strain pulse amplitude measured through UXRD. Linear chain model simulations accurately predict the timing and shape of UXRD and MOKE signals that are caused by the strain reflections from multiple interfaces in the heterostructure.