TY - JOUR A1 - Deb, Marwan A1 - Popova, Elena A1 - Hehn, Michel A1 - Keller, Niels A1 - Petit-Watelot, Sebastien A1 - Bargheer, Matias A1 - Mangin, Stephane A1 - Malinowski, Gregory T1 - Damping of Standing Spin Waves in Bismuth-Substituted Yttrium Iron Garnet as Seen via the Time-Resolved Magneto-Optical Kerr Effect JF - Physical review applied N2 - We investigate spin-wave resonance modes and their damping in insulating thin films of bismuth-substituted yttrium iron garnet by performing femtosecond magneto-optical pump-probe experiments. For large magnetic fields in the range below the magnetization saturation, we find that the damping of high-order standing spin-wave (SSW) modes is about 40 times lower than that for the fundamental one. The observed phenomenon can be explained by considering different features of magnetic anisotropy and exchange fields that, respectively, define the precession frequency for fundamental and high-order SSWs. These results provide further insight into SSWs in iron garnets and may be exploited in many new photomagnonic devices. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.12.044006 SN - 2331-7019 VL - 12 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Deb, Marwan A1 - Popova, Elena A1 - Hehn, Michel A1 - Keller, Niels A1 - Petit-Watelot, Sebastien A1 - Bargheer, Matias A1 - Mangin, Stephane A1 - Malinowski, Gregory T1 - Femtosecond Laser-Excitation-Driven High Frequency Standing Spin Waves in Nanoscale Dielectric Thin Films of Iron Garnets JF - Physical review letters N2 - We demonstrate that femtosecond laser pulses allow triggering high-frequency standing spin-wave modes in nanoscale thin films of a bismuth-substituted yttrium iron garnet. By varying the strength of the external magnetic field, we prove that two distinct branches of the dispersion relation are excited for all the modes. This is reflected in particular at a very weak magnetic field (similar to 33 mT) by a spin dynamics with a frequency up to 15 GHz, which is 15 times higher than the one associated with the ferromagnetic resonance mode. We argue that this phenomenon is triggered by ultrafast changes of the magnetic anisotropy via laser excitation of incoherent and coherent phonons. These findings open exciting prospects for ultrafast photo magnonics. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevLett.123.027202 SN - 0031-9007 SN - 1079-7114 VL - 123 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Liebig, Ferenc A1 - Henning, Ricky A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Schmitt, Clemens Nikolaus Zeno A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - A simple one-step procedure to synthesise gold nanostars in concentrated aqueous surfactant solutions JF - RSC Advances N2 - Due to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in the presence of Ag⁺ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption. KW - optical-properties KW - nanoparticles KW - sers KW - ultrafast KW - size KW - nanotriangles KW - nanoflowers KW - wavelength Y1 - 2019 U6 - https://doi.org/10.1039/C9RA02384D SN - 2046-2069 VL - 9 SP - 23633 EP - 23641 PB - RSC Publishing CY - London ER - TY - JOUR A1 - Pudell, Jan-Etienne A1 - Sander, M. A1 - Bauer, R. A1 - Bargheer, Matias A1 - Herzog, M. A1 - Gaál, Peter T1 - Full Spatiotemporal Control of Laser-Excited Periodic Surface Deformations JF - Physical review applied N2 - We demonstrate full control of acoustic and thermal periodic deformations at solid surfaces down to subnanosecond time scales and few-micrometer length scales via independent variation of the temporal and spatial phase of two optical transient grating (TG) excitations. For this purpose, we introduce an experimental setup that exerts control of the spatial phase of subsequent time-delayed TG excitations depending on their polarization state. Specific exemplary coherent control cases are discussed theoretically and corresponding experimental data are presented in which time-resolved x-ray reflectivity measures the spatiotemporal surface distortion of nanolayered heterostructures. Finally, we discuss examples where the application of our method may enable the control of functional material properties via tailored spatiotemporal strain fields. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevApplied.12.024036 SN - 2331-7019 VL - 12 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pudell, Jan-Etienne A1 - von Reppert, Alexander A1 - Schick, D. A1 - Zamponi, F. A1 - Rössle, Matthias A1 - Herzog, M. 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 - JOUR A1 - Sarhan, Radwan Mohamed A1 - Koopman, Wouter-Willem Adriaan A1 - Pudell, Jan-Etienne A1 - Stete, Felix A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Schmitt, Clemens Nikolaus Zeno A1 - Liebig, Ferenc A1 - Koetz, Joachim A1 - Bargheer, Matias T1 - Scaling up nanoplasmon catalysis BT - the role of heat dissipation JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Nanoscale heating by optical excitation of plasmonic nanoparticles offers a new perspective of controlling chemical reactions, where heat is not spatially uniform as in conventional macroscopic heating but strong temperature gradients exist around microscopic hot spots. In nanoplasmonics, metal particles act as a nanosource of light, heat, and energetic electrons driven by resonant excitation of their localized surface plasmon resonance. As an example of the coupling reaction of 4-nitrothiophenol into 4,4′-dimercaptoazobenzene, we show that besides the nanoscopic heat distribution at hot spots, the microscopic distribution of heat dictated by the spot size of the light focus also plays a crucial role in the design of plasmonic nanoreactors. Small sizes of laser spots enable high intensities to drive plasmon-assisted catalysis. This facilitates the observation of such reactions by surface-enhanced Raman scattering, but it challenges attempts to scale nanoplasmonic chemistry up to large areas, where the excess heat must be dissipated by one-dimensional heat transport. KW - Gold KW - Raman spectroscopy KW - Silicon KW - Irradiation KW - Lasers Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b12574 SN - 1932-7447 VL - 123 IS - 14 SP - 9352 EP - 9357 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sarhan, Radwan Mohamed A1 - Koopman, Wouter-Willem Adriaan A1 - Schuetz, Roman A1 - Schmid, Thomas A1 - Liebig, Ferenc A1 - Koetz, Joachim A1 - Bargheer, Matias T1 - The importance of plasmonic heating for the plasmondriven photodimerization of 4-nitrothiophenol JF - Scientific Reports N2 - Metal nanoparticles form potent nanoreactors, driven by the optical generation of energetic electrons and nanoscale heat. The relative influence of these two factors on nanoscale chemistry is strongly debated. This article discusses the temperature dependence of the dimerization of 4-nitrothiophenol (4-NTP) into 4,4′-dimercaptoazobenzene (DMAB) adsorbed on gold nanoflowers by Surface-Enhanced Raman Scattering (SERS). Raman thermometry shows a significant optical heating of the particles. The ratio of the Stokes and the anti-Stokes Raman signal moreover demonstrates that the molecular temperature during the reaction rises beyond the average crystal lattice temperature of the plasmonic particles. The product bands have an even higher temperature than reactant bands, which suggests that the reaction proceeds preferentially at thermal hot spots. In addition, kinetic measurements of the reaction during external heating of the reaction environment yield a considerable rise of the reaction rate with temperature. Despite this significant heating effects, a comparison of SERS spectra recorded after heating the sample by an external heater to spectra recorded after prolonged illumination shows that the reaction is strictly photo-driven. While in both cases the temperature increase is comparable, the dimerization occurs only in the presence of light. Intensity dependent measurements at fixed temperatures confirm this finding. KW - enhanced raman-scattering KW - charge-transfer KW - metal KW - nanoparticles KW - catalysis KW - AU KW - 4-nitrobenzenethiol KW - aminothiophenol KW - photocatalysis KW - wavelength Y1 - 2019 U6 - https://doi.org/10.1038/s41598-019-38627-2 SN - 2045-2322 VL - 9 PB - Macmillan Publishers Limited CY - London ER - TY - JOUR A1 - Tchoumba Kwamen, Christelle Larodia A1 - Rössle, Matthias A1 - Leitenberger, Wolfram A1 - Alexe, Marin A1 - Bargheer, Matias T1 - Time-resolved X-ray diffraction study of the structural dynamics in an epitaxial ferroelectric thin Pb(Zr0.2Ti0.8)O-3 film induced by sub-coercive fields JF - Applied physics letters N2 - The electric field-dependence of structural dynamics in a tetragonal ferroelectric lead zirconate titanate thin film is investigated under subcoercive and above-coercive fields using time-resolved X-ray diffraction. The domain nucleation and growth are monitored in real time during the application of an external field to the prepoled thin film capacitor. We propose the observed broadening of the in-plane peak width of the symmetric 002 Bragg reflection as an indicator of the domain disorder and discuss the processes that change the measured peak intensity. Subcoercive field switching results in remnant disordered domain configurations. Published under license by AIP Publishing. Y1 - 2019 U6 - https://doi.org/10.1063/1.5084104 SN - 0003-6951 SN - 1077-3118 VL - 114 IS - 16 PB - American Institute of Physics CY - Melville 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 - 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 -