TY  - JOUR
A1  - Koc, A.
A1  - Reinhardt, M.
A1  - von Reppert, Alexander
A1  - Rössle, Matthias
A1  - Leitenberger, Wolfram
A1  - Gleich, M.
A1  - Weinelt, M.
A1  - Zamponi, Flavio
A1  - Bargheer, Matias
T1  - Grueneisen-approach for the experimental determination of transient spin and phonon energies from ultrafast x-ray diffraction data: gadolinium
JF  - Journal of physics : Condensed matter
N2  - We study gadolinium thin films as a model system for ferromagnets with negative thermal expansion. Ultrashort laser pulses heat up the electronic subsystem and we follow the transient strain via ultrafast x-ray diffraction. In terms of a simple Grueneisen approach, the strain is decomposed into two contributions proportional to the thermal energy of spin and phonon subsystems. Our analysis reveals that upon femtosecond laser excitation, phonons and spins can be driven out of thermal equilibrium for several nanoseconds.
KW  - ultrafast
KW  - x-ray diffraction
KW  - magnetostriction
KW  - nonequilibrium
KW  - spin
KW  - phonon
KW  - rare earth
Y1  - 2017
U6  - https://doi.org/10.1088/1361-648X/aa7187
SN  - 0953-8984
SN  - 1361-648X
VL  - 29
SP  - 5884
EP  - 5891
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Koc, Azize
A1  - Reinhardt, M.
A1  - von Reppert, Alexander
A1  - Roessle, Matthias
A1  - Leitenberger, Wolfram
A1  - Dumesnil, K.
A1  - Gaal, Peter
A1  - Zamponi, Flavio
A1  - Bargheer, Matias
T1  - Ultrafast x-ray diffraction thermometry measures the influence of spin excitations on the heat transport through nanolayers
JF  - Physical review : B, Condensed matter and materials physics
N2  - We investigate the heat transport through a rare earth multilayer system composed of yttrium (Y), dysprosium (Dy), and niobium (Nb) by ultrafast x-ray diffraction. This is an example of a complex heat flow problem on the nanoscale, where several different quasiparticles carry the heat and conserve a nonequilibrium for more than 10 ns. The Bragg peak positions of each layer represent layer-specific thermometers that measure the energy flow through the sample after excitation of the Y top layer with fs-laser pulses. In an experiment-based analytic solution to the nonequilibrium heat transport problem, we derive the individual contributions of the spins and the coupled electron-lattice system to the heat conduction. The full characterization of the spatiotemporal energy flow at different starting temperatures reveals that the spin excitations of antiferromagnetic Dy speed up the heat transport into the Dy layer at low temperatures, whereas the heat transport through this layer and further into the Y and Nb layers underneath is slowed down. The experimental findings are compared to the solution of the heat equation using macroscopic temperature-dependent material parameters without separation of spin and phonon contributions to the heat. We explain why the simulated energy density matches our experiment-based derivation of the heat transport, although the simulated thermoelastic strain in this simulation is not even in qualitative agreement.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevB.96.014306
SN  - 2469-9950
SN  - 2469-9969
VL  - 96
PB  - American Physical Society
CY  - College Park
ER  -