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  - Sander, Mathias
A1  - Koc, A.
A1  - Kwamen, C. T.
A1  - Michaels, H.
A1  - von Reppert, Alexander
A1  - Pudell, Jan-Etienne
A1  - Zamponi, Flavio
A1  - Bargheer, Matias
A1  - Sellmann, J.
A1  - Schwarzkopf, J.
A1  - Gaal, P.
T1  - Characterization of an ultrafast Bragg-Switch for shortening hard x-ray pulses
JF  - Journal of applied physics
N2  - We present a nanostructured device that functions as photoacoustic hard x-ray switch. The device is triggered by femtosecond laser pulses and allows for temporal gating of hard x-rays on picosecond (ps) timescales. It may be used for pulse picking or even pulse shortening in 3rd generation synchrotron sources. Previous approaches mainly suffered from insufficient switching contrasts due to excitation-induced thermal distortions. We present a new approach where thermal distortions are spatially separated from the functional switching layers in the structure. Our measurements yield a switching contrast of 14, which is sufficient for efficient hard x-ray pulse shortening. The optimized structure also allows for utilizing the switch at high repetition rates of up to 208 kHz. Published by AIP Publishing.
Y1  - 2016
U6  - https://doi.org/10.1063/1.4967835
SN  - 0021-8979
SN  - 1089-7550
VL  - 120
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - von Reppert, Alexander
A1  - Puddell, J.
A1  - Koc, A.
A1  - Reinhardt, M.
A1  - Leitenberger, Wolfram
A1  - Dumesnil, K.
A1  - Zamponi, Flavio
A1  - Bargheer, Matias
T1  - Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet
JF  - Structural dynamics
N2  - We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.
Y1  - 2016
U6  - https://doi.org/10.1063/1.4961253
SN  - 2329-7778
VL  - 3
PB  - AIP Publishing LLC
CY  - Melville, NY
ER  - 
TY  - JOUR
A1  - von Reppert, Alexander
A1  - Pudell, Jan-Etienne
A1  - Koc, A.
A1  - Reinhardt, M.
A1  - Leitenberger, Wolfram
A1  - Dumesnil, K.
A1  - Zamponi, Flavio
A1  - Bargheer, Matias
T1  - Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet
JF  - Structural dynamics
N2  - We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Neel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. (C) 2016 Author(s).
Y1  - 2016
U6  - https://doi.org/10.1063/1.4961253
SN  - 2329-7778
VL  - 3
PB  - American Institute of Physics
CY  - Melville
ER  -