TY - JOUR A1 - Zeuschner, Steffen A1 - Parpiiev, Tymur A1 - Pezeril, Thomas A1 - Hillion, Arnaud A1 - Dumesnil, Karine A1 - Anane, Abdelmadjid A1 - Pudell, Jan-Etienne A1 - Willig, Lisa A1 - Rössle, Matthias A1 - Herzog, Marc A1 - von Reppert, Alexander A1 - Bargheer, Matias T1 - Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction JF - Structural Dynamics N2 - 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 if the excited TbFe2 surface terminates the sample and a decomposition of the strain wavepacket into an asymmetric bipolar and a unipolar pulse, if 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. KW - Heterostructures KW - Magnetooptical effects KW - Metal oxides KW - Crystal lattices KW - Transition metals KW - Magnetism KW - Ultrafast X-ray diffraction KW - Lasers KW - Bragg peak KW - Phonons Y1 - 2019 U6 - https://doi.org/10.1063/1.5084140 SN - 2329-7778 VL - 6 IS - 2 PB - AIP Publishing LLC CY - Melville, NY ER - TY - GEN A1 - Zeuschner, Steffen A1 - Parpiiev, Tymur A1 - Pezeril, Thomas A1 - Hillion, Arnaud A1 - Dumesnil, Karine A1 - Anane, Abdelmadjid A1 - Pudell, Jan-Etienne A1 - Willig, Lisa A1 - Rössle, Matthias A1 - Herzog, Marc A1 - von Reppert, Alexander A1 - Bargheer, Matias T1 - Tracking picosecond strain pulses in heterostructures that exhibit giant magnetostriction T2 - Postprints der Universität Potsdam : Mathematisch-naturwissenschaftliche Reihe N2 - 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 if the excited TbFe2 surface terminates the sample and a decomposition of the strain wavepacket into an asymmetric bipolar and a unipolar pulse, if 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 706 KW - Heterostructures KW - Magnetooptical effects KW - Metal oxides KW - Crystal lattices KW - Transition metals KW - Magnetism KW - Ultrafast X-ray diffraction KW - Lasers KW - Bragg peak KW - Phonons Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-428457 SN - 1866-8372 IS - 706 ER - TY - JOUR A1 - Willig, Lisa A1 - von Reppert, Alexander A1 - Deb, Marwan A1 - Ganss, F. A1 - Hellwig, O. A1 - Bargheer, Matias T1 - Finite-size effects in ultrafast remagnetization dynamics of FePt JF - Physical review : B, Condensed matter and materials physics N2 - We investigate the ultrafast magnetization dynamics of FePt in the L1(0) phase after an optical heating pulse, as used in heat-assisted magnetic recording. We compare continuous and nano-granular thin films and emphasize the impact of the finite size on the remagnetization dynamics. The remagnetization speeds up significantly with increasing external magnetic field only for the continuous film, where domain-wall motion governs the dynamics. The ultrafast remagnetization dynamics in the continuous film are only dominated by heat transport in the regime of high magnetic fields, whereas the timescale required for cooling is prevalent in the granular film for all magnetic field strengths. These findings highlight the necessary conditions for studying the intrinsic heat transport properties in magnetic materials. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevB.100.224408 SN - 2469-9950 SN - 2469-9969 VL - 100 IS - 22 PB - American Physical Society CY - College Park ER - 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 - von Reppert, Alexander A1 - Sarhan, Radwan Mohamed A1 - Stete, Felix A1 - Pudell, Jan-Etienne A1 - Del Fatti, N. A1 - Crut, A. A1 - Koetz, Joachim A1 - Liebig, Ferenc A1 - Prietzel, Claudia Christina A1 - Bargheer, Matias T1 - Watching the Vibration and Cooling of Ultrathin Gold Nanotriangles by Ultrafast X-ray Diffraction JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - We study the vibrations of ultrathin gold nanotriangles upon optical excitation of the electron gas by ultrafast X-ray diffraction. We quantitatively measure the strain evolution in these highly asymmetric nano-objects, providing a direct estimation of the amplitude and phase of the excited vibrational motion. The maximal strain value is well reproduced by calculations addressing pump absorption by the nanotriangles and their resulting thermal expansion. The amplitude and phase of the out-of-plane vibration mode with 3.6 ps period dominating the observed oscillations are related to two distinct excitation mechanisms. Electronic and phonon pressures impose stresses with different time dependences. The nanosecond relaxation of the expansion yields a direct temperature sensing of the nano-object. The presence of a thin organic molecular layer at the nanotriangle/substrate interfaces drastically reduces the thermal conductance to the substrate. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpcc.6b11651 SN - 1932-7447 VL - 120 SP - 28894 EP - 28899 PB - American Chemical Society CY - Washington 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 - 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 - GEN 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 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 272 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-98710 ER - TY - JOUR A1 - von Reppert, Alexander A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Zeuschner, Steffen Peer A1 - Dumesnil, Karine A1 - Bargheer, Matias T1 - Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer JF - Structural Dynamics N2 - Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses. KW - Strain measurement KW - Photoexcitations KW - Crystal lattices KW - Femtosecond lasers KW - Thermal effects KW - Heterostructures KW - Ultrafast X-rays KW - Phonons Y1 - 2020 U6 - https://doi.org/10.1063/1.5145315 SN - 2329-7778 VL - 7 IS - 024303 PB - AIP Publishing LLC CY - Melville, NY ER - TY - GEN A1 - von Reppert, Alexander A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Zeuschner, Steffen Peer A1 - Dumesnil, Karine A1 - Bargheer, Matias T1 - Unconventional picosecond strain pulses resulting from the saturation of magnetic stress within a photoexcited rare earth layer T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 899 KW - Strain measurement KW - Photoexcitations KW - Crystal lattices KW - Femtosecond lasers KW - Thermal effects KW - Heterostructures KW - Ultrafast X-rays KW - Phonons Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-469350 SN - 1866-8372 IS - 899 ER - TY - THES A1 - von Reppert, Alexander T1 - Magnetic strain contributions in laser-excited metals studied by time-resolved X-ray diffraction T1 - Untersuchung magnetischer Beiträge zur Ausdehnung laserangeregter Metalle mittels zeitaufgelöster Röntgenbeugungsexperimente N2 - In this work I explore the impact of magnetic order on the laser-induced ultrafast strain response of metals. Few experiments with femto- or picosecond time-resolution have so far investigated magnetic stresses. This is contrasted by the industrial usage of magnetic invar materials or magnetostrictive transducers for ultrasound generation, which already utilize magnetostrictive stresses in the low frequency regime. In the reported experiments I investigate how the energy deposition by the absorption of femtosecond laser pulses in thin metal films leads to an ultrafast stress generation. I utilize that this stress drives an expansion that emits nanoscopic strain pulses, so called hypersound, into adjacent layers. Both the expansion and the strain pulses change the average inter-atomic distance in the sample, which can be tracked with sub-picosecond time resolution using an X-ray diffraction setup at a laser-driven Plasma X-ray source. Ultrafast X-ray diffraction can also be applied to buried layers within heterostructures that cannot be accessed by optical methods, which exhibit a limited penetration into metals. The reconstruction of the initial energy transfer processes from the shape of the strain pulse in buried detection layers represents a contribution of this work to the field of picosecond ultrasonics. A central point for the analysis of the experiments is the direct link between the deposited energy density in the nano-structures and the resulting stress on the crystal lattice. The underlying thermodynamical concept of a Grüneisen parameter provides the theoretical framework for my work. I demonstrate how the Grüneisen principle can be used for the interpretation of the strain response on ultrafast timescales in various materials and that it can be extended to describe magnetic stresses. The class of heavy rare-earth elements exhibits especially large magnetostriction effects, which can even lead to an unconventional contraction of the laser-excited transducer material. Such a dominant contribution of the magnetic stress to the motion of atoms has not been demonstrated previously. The observed rise time of the magnetic stress contribution in Dysprosium is identical to the decrease in the helical spin-order, that has been found previously using time-resolved resonant X-ray diffraction. This indicates that the strength of the magnetic stress can be used as a proxy of the underlying magnetic order. Such magnetostriction measurements are applicable even in case of antiparallel or non-collinear alignment of the magnetic moments and a vanishing magnetization. The strain response of metal films is usually determined by the pressure of electrons and lattice vibrations. I have developed a versatile two-pulse excitation routine that can be used to extract the magnetic contribution to the strain response even if systematic measurements above and below the magnetic ordering temperature are not feasible. A first laser pulse leads to a partial ultrafast demagnetization so that the amplitude and shape of the strain response triggered by the second pulse depends on the remaining magnetic order. With this method I could identify a strongly anisotropic magnetic stress contribution in the magnetic data storage material iron-platinum and identify the recovery of the magnetic order by the variation of the pulse-to-pulse delay. The stark contrast of the expansion of iron-platinum nanograins and thin films shows that the different constraints for the in-plane expansion have a strong influence on the out-of-plane expansion, due to the Poisson effect. I show how such transverse strain contributions need to be accounted for when interpreting the ultrafast out-of-plane strain response using thermal expansion coefficients obtained in near equilibrium conditions. This work contributes an investigation of magnetostriction on ultrafast timescales to the literature of magnetic effects in materials. It develops a method to extract spatial and temporal varying stress contributions based on a model for the amplitude and shape of the emitted strain pulses. Energy transfer processes result in a change of the stress profile with respect to the initial absorption of the laser pulses. One interesting example occurs in nanoscopic gold-nickel heterostructures, where excited electrons rapidly transport energy into a distant nickel layer, that takes up much more energy and expands faster and stronger than the laser-excited gold capping layer. Magnetic excitations in rare earth materials represent a large energy reservoir that delays the energy transfer into adjacent layers. Such magneto-caloric effects are known in thermodynamics but not extensively covered on ultrafast timescales. The combination of ultrafast X-ray diffraction and time-resolved techniques with direct access to the magnetization has a large potential to uncover and quantify such energy transfer processes. N2 - In dieser Arbeit untersuche ich den Einfluss magnetischer Ordnung auf die laser-induzierte, ultraschnelle Ausdehnung von Metallen. In Experimenten mit Femto- oder Pikosekunden Zeitauflösung sind magnetische Drücke bisher kaum erforscht. Dies steht im Kontrast zur industriellen Verwendung von magnetischen Invar Materialien oder magnetostriktiven Ultraschallgebern, in denen magnetische Drücke bereits in niedrigeren Frequenzbereichen Anwendung finden. In meinen Experimenten untersuche ich, wie der Energieeintrag durch die Absorption von Femtosekunden-Laserpulsen in dünnen Metallschichten zu einem ultraschnellen Druckanstieg führt. Dabei nutze ich, dass der Druckanstieg zu einer Ausdehnung führt, welche Deformationswellen auf der Nanometerskala, sogenannte Hyperschallpulse, in angrenzende Schichten aussendet. Sowohl die Ausdehnung als auch die Deformationspulse ändern den mittleren Abstand zwischen den Atomen in der Probe, welcher mittels Röntgenbeugung an einer Laser-getriebenen Plasma-Röntgenquelle mit einer Subpikosekunden-Zeitauflösung detektiert wird. Das Verfahren der ultraschnellen Röntgenbeugung gelingt auch in Heterostrukturen mit vergrabenen Detektionsschichten, zu denen optische Methoden aufgrund ihrer limitierter Eindringtiefe in Metallen keinen Zugang haben. Ein Beitrag dieser Arbeit zum Feld der Pikosekunden-Akustik ist es, aus der Ausdehnung einer solchen Detektionsschicht Rückschlüsse auf die initialen Energietransferprozesse zu ziehen. Der direkte Zusammenhang zwischen der eingebrachten Energiedichte in die Nanostrukturen und dem resultierenden Druck auf das Atomgitter ist ein zentraler Punkt in meiner Analyse der Experimente. Das zu Grunde liegende thermodynamische Konzept des Grüneisen-Parameters bildet den theoretischen Kontext meiner Publikationen. Anhand verschiedener Materialien demonstriere ich, wie dieses Prinzip auch zur Analyse der Ausdehnung auf ultraschnellen Zeitskalen verwendet werden kann und sich auch auf magnetische Drücke übertragen lässt. Insbesondere in der Materialklasse der schweren, seltenen Erdelemente sind Magnetostriktionseffekte sehr groß und führen dort sogar zu einem ungewöhnlichen Zusammenziehen des Materials nach der Laseranregung. Solch ein bestimmender Einfluss des magnetischen Drucks auf die Atombewegung ist bisher nicht gezeigt worden. Die Zeitskala des magnetischen Druckanstiegs entspricht dabei der beobachteten Abnahme der helikalen Spin-Ordnung, welche zuvor mittels zeitaufgelöster, resonanter Röntgenbeugung ermittelt wurde. Dies zeigt, dass die Stärke des magnetischen Drucks als Maß für magnetische Ordnung dienen kann, insbesondere auch im Fall von antiparalleler oder nicht-kollinearer Ordnung der magnetischen Momente in Proben mit verschwindender Magnetisierung. In Metallfilmen ist die Dehnung des Atomgitters in der Regel durch Druck von Elektronen und Gitterschwingungen geprägt. Um den magnetischen Druckbeitrag auch in solchen Fällen zu extrahieren, in denen systematische Experimente oberhalb und unterhalb der magnetischen Ordnungstemperatur nicht praktikabel sind, habe ich ein neuartiges Doppelpuls-Anregungsverfahren entwickelt, welches allgemein für die Untersuchung von Phasenübergängen nützlich ist. Der Energieeintrag durch den ersten Laserpuls führt dabei zu einer partiellen, ultraschnellen Demagnetisierung, sodass die Amplitude und Form der Gitterausdehnung nach dem zweiten Puls von der Stärke des verbliebenen magnetischen Drucks und somit von der verbliebenen magnetischen Ordnung abhängt. Mit dieser Methode ist es möglich geworden, einen stark richtungsabhängigen, magnetischen Druckbeitrag im Speichermedium Eisen-Platin zu identifizieren und mittels Variation des Puls-zu-Puls Abstands auch die Rückkehr der magnetischen Ordnung zu zeigen. Die unterschiedliche Ausdehnung von Eisen-Platin Nanopartikeln und dünnen Filmen zeigt dabei, dass die verschiedenen Zwangsbedingungen für die Ausdehnung entlang der Probenoberfläche aufgrund des Poisson-Effekts einen entscheidenden Einfluss auf die ultraschnelle Ausdehnung senkrecht zur Probenoberfläche hat. Ich analysiere, wie die zugrunde liegende Querkontraktion bei der Interpretation der ultraschnellen Ausdehnung auf der Basis von thermischen Ausdehnungskoeffizienten im Quasi-Gleichgewicht berücksichtigt werden kann. Meine Arbeit erweitert die Literatur um einen Beitrag zur ultraschnellen Magnetostriktion und entwickelt eine Methodik mittels derer räumlich und zeitlich variierende Druckbeiträge anhand einer Modellierung der Form der Deformationswellen extrahiert werden können. Energietransferprozesse spiegeln sich dabei durch eine Änderung des Druckprofils gegenüber dem Absorptionsprofil der Laserpulse wider. KW - lattice dynamics KW - magnetism KW - ultrafast KW - X-ray diffraction KW - Gitterdynamik KW - Magnetismus KW - ultraschnell KW - Röntgenbeugung Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-535582 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 - Pudell, Jan-Etienne A1 - von Reppert, Alexander A1 - Schick, D. A1 - Zamponi, F. A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Zabel, Hartmut A1 - Bargheer, Matias T1 - Ultrafast negative thermal expansion driven by spin disorder JF - Physical review : B, Condensed matter and materials physics N2 - We measure the transient strain profile in a nanoscale multilayer system composed of yttrium, holmium, and niobium after laser excitation using ultrafast x-ray diffraction. The strain propagation through each layer is determined by transient changes in the material-specific Bragg angles. We experimentally derive the exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical penetration depth. Below the Neel temperature of Ho, the optical excitation triggers negative thermal expansion, which is induced by a quasi-instantaneous contractive stress and a second contractive stress contribution increasing on a 12-ps timescale. These two timescales were recently measured for the spin disordering in Ho [Rettig et al., Phys. Rev. Lett. 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar strain pulse with an inverted sign traveling through the heterostructure. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevB.99.094304 SN - 2469-9950 SN - 2469-9969 VL - 99 IS - 9 PB - American Physical Society CY - College Park ER - TY - GEN A1 - Pudell, Jan-Etienne A1 - Maznev, Alexei A1 - Herzog, Marc A1 - Kronseder, M. A1 - Back, Christian 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 T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 797 KW - thin magnetic layers KW - optical-excitation KW - heat-capacity KW - electron KW - gold KW - dynamics Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-426233 SN - 1866-8372 IS - 797 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 - TY - JOUR A1 - Mattern, Maximilian A1 - von Reppert, Alexander A1 - Zeuschner, Steffen Peer A1 - Pudell, Jan-Etienne A1 - Kühne, F. A1 - Diesing, Detlef A1 - Herzog, Marc A1 - Bargheer, Matias T1 - Electronic energy transport in nanoscale Au/Fe hetero-structures in the perspective of ultrafast lattice dynamics JF - Applied physics letters N2 - We study the ultrafast electronic transport of energy in a photoexcited nanoscale Au/Fe hetero-structure by modeling the spatiotemporal profile of energy densities that drives transient strain, which we quantify by femtosecond x-ray diffraction. This flow of energy is relevant for intrinsic demagnetization and ultrafast spin transport. We measured lattice strain for different Fe layer thicknesses ranging from few atomic layers to several nanometers and modeled the spatiotemporal flow of energy densities. The combination of a high electron-phonon coupling coefficient and a large Sommerfeld constant in Fe is found to yield electronic transfer of nearly all energy from Au to Fe within the first hundreds of femtoseconds. Y1 - 2022 U6 - https://doi.org/10.1063/5.0080378 SN - 0003-6951 SN - 1077-3118 VL - 120 IS - 9 PB - AIP Publishing CY - Melville ER - TY - JOUR A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Dumesnil, Karine A1 - von Reppert, Alexander A1 - Bargheer, Matias T1 - Towards shaping picosecond strain pulses via magnetostrictive transducers JF - Photoacoustics N2 - Using time-resolved x-ray diffraction, we demonstrate the manipulation of the picosecond strain response of a metallic heterostructure consisting of a dysprosium (Dy) transducer and a niobium (Nb) detection layer by an external magnetic field. We utilize the first-order ferromagnetic–antiferromagnetic phase transition of the Dy layer, which provides an additional large contractive stress upon laser excitation compared to its zerofield response. This enhances the laser-induced contraction of the transducer and changes the shape of the picosecond strain pulses driven in Dy and detected within the buried Nb layer. Based on our experiment with rare-earth metals we discuss required properties for functional transducers, which may allow for novel field-control of the emitted picosecond strain pulses. KW - picosecond ultrasonics KW - magnetostriction KW - ultrafast x-ray diffraction KW - ultrafast photoacoustics KW - nanoscale heat transfer KW - negative thermal expansion Y1 - 2023 U6 - https://doi.org/10.1016/j.pacs.2023.100463 SN - 2213-5979 VL - 30 PB - Elsevier CY - Amsterdam ER - TY - GEN A1 - Mattern, Maximilian A1 - Pudell, Jan-Etienne A1 - Dumesnil, Karine A1 - von Reppert, Alexander A1 - Bargheer, Matias T1 - Towards shaping picosecond strain pulses via magnetostrictive transducers T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Using time-resolved x-ray diffraction, we demonstrate the manipulation of the picosecond strain response of a metallic heterostructure consisting of a dysprosium (Dy) transducer and a niobium (Nb) detection layer by an external magnetic field. We utilize the first-order ferromagnetic–antiferromagnetic phase transition of the Dy layer, which provides an additional large contractive stress upon laser excitation compared to its zerofield response. This enhances the laser-induced contraction of the transducer and changes the shape of the picosecond strain pulses driven in Dy and detected within the buried Nb layer. Based on our experiment with rare-earth metals we discuss required properties for functional transducers, which may allow for novel field-control of the emitted picosecond strain pulses. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1321 KW - picosecond ultrasonics KW - magnetostriction KW - ultrafast x-ray diffraction KW - ultrafast photoacoustics KW - nanoscale heat transfer KW - negative thermal expansion Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-588868 SN - 1866-8372 IS - 1321 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 - 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 - Herzog, Marc A1 - von Reppert, Alexander A1 - Pudell, Jan-Etienne A1 - Henkel, Carsten A1 - Kronseder, Matthias A1 - Back, Christian H. A1 - Maznev, Alexei A. A1 - Bargheer, Matias T1 - Phonon-dominated energy transport in purely metallic heterostructures JF - Advanced functional materials N2 - Ultrafast X-ray diffraction is used to quantify the transport of energy in laser-excited nanoscale gold-nickel (Au-Ni) bilayers. Electron transport and efficient electron-phonon coupling in Ni convert the laser-deposited energy in the conduction electrons within a few picoseconds into a strong non-equilibrium between hot Ni and cold Au phonons at the bilayer interface. Modeling of the subsequent equilibration dynamics within various two-temperature models confirms that for ultrathin Au films, the thermal transport is dominated by phonons instead of conduction electrons because of the weak electron-phonon coupling in Au. KW - heterostructures KW - nanoscale energy transports KW - non-equilibrium KW - thermal KW - transports KW - ultrafast phenomena Y1 - 2022 U6 - https://doi.org/10.1002/adfm.202206179 SN - 1616-301X SN - 1616-3028 VL - 32 IS - 41 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Bojahr, Andre A1 - Gohlke, Matthias A1 - Leitenberger, Wolfram A1 - Pudell, Jan-Etienne A1 - Reinhardt, Matthias A1 - von Reppert, Alexander A1 - Rössle, Matthias A1 - Sander, Mathias A1 - Gaal, Peter A1 - Bargheer, Matias T1 - Second Harmonic Generation of Nanoscale Phonon Wave Packets JF - Physical review letters N2 - Phonons are often regarded as delocalized quasiparticles with certain energy and momentum. The anharmonic interaction of phonons determines macroscopic properties of the solid, such as thermal expansion or thermal conductivity, and a detailed understanding becomes increasingly important for functional nanostructures. Although phonon-phonon scattering processes depicted in simple wave-vector diagrams are the basis of theories describing these macroscopic phenomena, experiments directly accessing these coupling channels are scarce. We synthesize monochromatic acoustic phonon wave packets with only a few cycles to introduce nonlinear phononics as the acoustic counterpart to nonlinear optics. Control of the wave vector, bandwidth, and consequently spatial extent of the phonon wave packets allows us to observe nonlinear phonon interaction, in particular, second harmonic generation, in real time by wave-vector-sensitive Brillouin scattering with x-rays and optical photons. Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevLett.115.195502 SN - 0031-9007 SN - 1079-7114 VL - 115 IS - 19 PB - American Physical Society CY - College Park ER -