TY  - JOUR
A1  - von Reppert, Alexander
A1  - Willig, Lisa
A1  - Pudell, Jan-Etienne
A1  - Roessle, M.
A1  - Leitenberger, Wolfram
A1  - Herzog, Marc
A1  - Ganss, F.
A1  - Hellwig, O.
A1  - Bargheer, Matias
T1  - Ultrafast laser generated strain in granular and continuous FePt thin films
JF  - Applied physics letters
N2  - We employ ultrafast X-ray diffraction to compare the lattice dynamics of laser-excited continuous and granular FePt films on MgO (100) substrates. Contrary to recent results on free-standing granular films, we observe in both cases a pronounced and long-lasting out-of-plane expansion. We attribute this discrepancy to the in-plane expansion, which is suppressed by symmetry in continuous films. Granular films on substrates are less constrained and already show a reduced out-of-plane contraction. Via the Poisson effect, out-of-plane contractions drive in-plane expansion and vice versa. Consistently, the granular film exhibits a short-lived out-of-plane contraction driven by ultrafast demagnetization which is followed by a reduced and delayed expansion. From the acoustic reflections of the observed strain waves at the film-substrate interface, we extract a 13% reduction of the elastic constants in thin 10 nm FePt films compared to bulk-like samples. (C) 2018 Author(s).
Y1  - 2018
U6  - https://doi.org/10.1063/1.5050234
SN  - 0003-6951
SN  - 1077-3118
VL  - 113
IS  - 12
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Pudell, Jan-Etienne
A1  - Maznev, A. A.
A1  - Herzog, Marc
A1  - Kronseder, M.
A1  - Back, Christian H.
A1  - Malinowski, Gregory
A1  - von Reppert, Alexander
A1  - Bargheer, Matias
T1  - Layer specific observation of slow thermal equilibration in ultrathin metallic nanostructures by femtosecond X-ray diffraction
JF  - Nature Communications
N2  - Ultrafast heat transport in nanoscale metal multilayers is of great interest in the context of optically induced demagnetization, remagnetization and switching. If the penetration depth of light exceeds the bilayer thickness, layer-specific information is unavailable from optical probes. Femtosecond diffraction experiments provide unique experimental access to heat transport over single digit nanometer distances. Here, we investigate the structural response and the energy flow in the ultrathin double-layer system: gold on ferromagnetic nickel. Even though the excitation pulse is incident from the Au side, we observe a very rapid heating of the Ni lattice, whereas the Au lattice initially remains cold. The subsequent heat transfer from Ni to the Au lattice is found to be two orders of magnitude slower than predicted by the conventional heat equation and much slower than electron-phonon coupling times in Au. We present a simplified model calculation highlighting the relevant thermophysical quantities.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-05693-5
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  -