Search

Your search keyword '"Lüpke, G."' showing total 237 results
Start Over Author "Lüpke, G."
237 results on '"Lüpke, G."'

1. Ultrafast optical observation of spin-pumping induced dynamic exchange coupling in ferromagnetic semiconductor/metal bilayer

Author

Liu, X., Liu, P., Yuan, H. C., Shi, J. Y., Wang, H. L., Nie, S. H., Jin, F., Zheng, Z., Yu, X. Z., Zhao, J. H., Zhao, H. B., and Lüpke, G.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons, Physics - Applied Physics
Abstract

Spin angular momentum transfer in magnetic bilayers offers the possibility of ultrafast and low-loss operation for next-generation spintronic devices. We report the field- and temperature- dependent measurements on the magnetization precessions in Co$_2$FeAl/(Ga,Mn)As by time-resolved magneto-optical Kerr effect (TRMOKE). Analysis of the effective Gilbert damping and phase shift indicates a clear signature of an enhanced dynamic exchange coupling between the two ferromagnetic (FM) layers due to the reinforced spin pumping at resonance. The temperature dependence of the dynamic exchange-coupling reveals a primary contribution from the ferromagnetism in (Ga,Mn)As., Comment: arXiv admin note: text overlap with arXiv:2203.00293

Published
2022
Full Text
View/download PDF

2. Ultrafast enhancement of interfacial exchange coupling in ferromagnetic bilayer

Author

Liu, X., Yuan, H. C., Liu, P., Shi, J. Y., Wang, H. L., Nie, S. H., Jin, F., Zheng, Z., Yu, X. Z., Zhao, J. H., Zhao, H. B., and Lüpke, G.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons, Physics - Applied Physics
Abstract

Fast spin manipulation in magnetic heterostructures, where magnetic interactions between different materials often define the functionality of devices, is a key issue in the development of ultrafast spintronics. Although recently developed optical approaches such as ultrafast spin-transfer and spin-orbit torques open new pathways to fast spin manipulation, these processes do not fully utilize the unique possibilities offered by interfacial magnetic coupling effects in ferromagnetic multilayer systems. Here, we experimentally demonstrate ultrafast photo-enhanced interfacial exchange interactions in the ferromagnetic Co$_2$FeAl/(Ga,Mn)As system at low laser fluence levels. The excitation efficiency of Co$_2$FeAl with the (Ga,Mn)As layer is 30-40 times higher than the case with the GaAs layer at 5 K due to a photo-enhanced exchange coupling interaction via photoexcited charge transfer between the two ferromagnetic layers. In addition, the coherent spin precessions persist to room temperature, excluding the drive of photo-enhanced magnetization in the (Ga,Mn)As layer and indicating a proximity-effect-related optical excitation mechanism. The results highlight the importance of considering the range of interfacial exchange interactions in ferromagnetic heterostructures and how these magnetic coupling effects can be utilized for ultrafast, low-power spin manipulation.

Published
2022

3. Scaling of intrinsic Gilbert damping with spin-orbital coupling strength

Author

He, Pan, Ma, X., Zhang, J. W., Zhao, H. B., Lüpke, G., Shi, Z., and Zhou, S. M.

Subjects
Condensed Matter - Materials Science
Abstract

We have experimentally and theoretically investigated the dependence of the intrinsic Gilbert damping parameter $\alpha_0$ on the spin-orbital coupling strength $\xi$ by using L1$_{\mathrm{0}}$ ordered FePd$_{\mathrm{1-x}}$Pt$_{\mathrm{x}}$ ternary alloy films with perpendicular magnetic anisotropy. With the time-resolved magneto-optical Kerr effect, $\alpha_0$ is found to increase by more than a factor of ten when $x$ varies from 0 to 1.0. Since changes of other leading parameters are found to be neglected, the $\alpha_0$ has for the first time been proven to be proportional to $\xi^2$., Comment: 4 pages, 5 figures

Published
2012
Full Text
View/download PDF

4. Viscous spin exchange torque on precessional magnetization in $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_{n}$ superlattices

Author

Zhao, H. B., Smith, K. J., Fan, Y., Lüpke, G., Bhattacharya, A., Bader, S. D., Warusawithana, M., Zhai, X., and Eckstein, J. N.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

Photoinduced magnetization dynamics is investigated in chemically ordered $(\mathrm{LaMnO}_3)_{2n}/(\mathrm{SrMnO}_3)_n$ superlattices using the time-resolved magneto-optic Kerr effect. A monotonic frequency-field dependence is observed for the $n=1$ superlattice, indicating a single spin population consistent with a homogeneous hole distribution. In contrast, for $n\geq2$ superlattices, a large precession frequency is observed at low fields indicating the presence of an exchange torque in the dynamic regime. We propose a model that ascribes the emergence of exchange torque to the coupling between two spin populations -- viscous and fast spins., Comment: 5 pages, 4 figures

Published
2007
Full Text
View/download PDF

5. Evidence for High-Temperature Superconductivity in Doped Laser-Processed Sr-Ru-O

Author

Gulian, A. M., Wood, K. S., Van Vechten, D., Claassen, J., Soulen, Jr., R. J., Qadri, S., Osofsky, M., Lucarelli, A., Luepke, G., Badalyan, G. R., Kuzanyan, V. S., Kuzanyan, A. S., and Nikoghosyan, V. R.

Subjects
Condensed Matter - Superconductivity
Abstract

We have discovered that samples of a new material produced by special processing of crystals of Sr2RuO4 (which is known to be a triplet superconductor with Tc values ~1.0-1.5K) exhibit signatures of superconductivity (zero DC resistance and expulsion of magnetic flux) at temperatures exceeding 200K. The special processing includes deposition of a silver coating and laser micromachining; Ag doping and enhanced oxygen are observed in the resultant surface layer. The transition, whether measured resistively or by magnetic field expulsion, is broad. When the transition is registered by resistive methods, the critical temperature is markedly reduced when the measuring current is increased. The resistance disappears by about 190K. The highest value of Tc registered by magneto-optical visualization is about 220K and even higher values (up to 250K) are indicated from the SQUID-magnetometer measurements.

Published
2005

12. Carrier relaxation time divergence in single and double layer cuprates

Author

Schneider, M. L., Rast, S., Onellion, M., Demsar, J., Taylor, A. J., Glinka, Y., Tolk, N. H., Ren, Y. H., Lüpke, G., Klimov, A., Xu, Y., Sobolewski, R., Si, W., Zeng, X. H., Soukiassian, A., Xi, X. X., Abrecht, M., Ariosa, D., Pavuna, D., Krapf, A., Manzke, R., Printz, J. O., Williamsen, M. S., Downum, K. E., Guptasarma, P., and Bozovic, I.

Published
2003
Full Text
View/download PDF

17. Ultrafast photoinduced reflectivity transients in doped manganite.

Author

Ren, Y. H., Zhao, H. B., Lüpke, G., Hong, C. S., Hur, N. H., Hu, Y.F., and Qi Li

Subjects
REFLECTANCE, MAGNETIC fields, QUASIPARTICLES, TEMPERATURE, QUANTUM theory, PHONONS
Abstract

The temperature and magnetic field dependence of ultrafast photoinduced spin and quasiparticle relaxation dynamics is reported in La0.67Ca0.33MnO3 and LaMnO3 single crystals and thin films. Both manganites reveal an unusually slow (∼10 μs) carrier relaxation process attributed to the spin-lattice relaxation in localized states. The quasiparticle dynamics is governed by the temperature- and magnetic field-dependent pseudogap in La0.67Ca0.33MnO3, and by the temperature-independent Jahn–Teller gap in LaMnO3. The loss of spectral weight near the Fermi level in La0.67Ca0.33MnO3 strongy affects the quasiparticle relaxation dynamics as temperature increases from below TC. Our results show that the coupled dynamics of charge, spin and lattice is strongly correlated with the distinct gap structures in these manganites. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
Full Text
View/download PDF

18. Vibrational lifetimes of hydrogen in silicon.

Author

Lüpke, G., Tolk, N. H., and Feldman, L. C.

Subjects
*VIBRATION (Mechanics), *HYDROGEN, *SILICON, *SEMICONDUCTORS
Abstract

Characterization of defect and impurity reactions, dissociation, and migration in semiconductors requires a detailed understanding of the rates and pathways of vibrational energy flow, of the energy transfer channels, and of the coupling mechanisms between local modes and the phonon bath of the host material. Significant progress in reaching this goal has been accomplished in recent landmark studies exploring the excitation and dynamics of vibrational states associated with hydrogen in silicon. The lifetime of the Si-H stretch mode is found to be extremely dependent on the local solid-state structure, ranging from picoseconds for interstitial-like hydrogen, hundreds of picoseconds for hydrogen-vacancy complexes, to several nanoseconds for hydrogen bonded to Si surfaces—over three orders of magnitude variation. Such large variations in lifetime (transition probability) are extraordinarily rare in solid-state science. The level of theoretical investigation into the vibrational lifetime of the Si-H oscillator is less advanced. This state of affairs is partly because of the difficulties in explicitly treating slow relaxation processes in complex systems, and partly because, as suggested by experiment, a highly anharmonic coupling mechanism is apparently responsible for the (multiphonon) relaxation process. Even more importantly, because of the high frequency of the Si-H stretching motion, a quantum mechanical treatment of the Si-H oscillator is required. A combination of Bloch-Redfield theory and molecular dynamics simulation seems promising in describing the relaxation process of the Si-H vibrational modes. It is the aim of this review article to present a comprehensive overview of the recent accomplishments, current understandings, and future directions in this emerging field of time-resolved vibrational spectroscopy of point defects in solids. [ABSTRACT FROM AUTHOR]

Published
2003

23. Determination of the crystallographic orientation of cubic media to high resolution using optical harmonic generation.

Author

Bottomley, D. J., Lüpke, G., Mihaychuk, J. G., and van Driel, H. M.

Subjects
*CRYSTALLOGRAPHY, *SEMICONDUCTORS, *SECOND harmonic generation
Abstract

Presents a study which showed how second-harmonic (SH) and third-harmonic (TH) generation can be used to derive the crystallographic orientation of noncentrosymmetric and centrosymmetric cubic semiconductors. Theoretical framework of the study; Experimental methods; Measurement of the SH and TH data from the vicinal gallium arsenide and silicon.

Published
1993
Full Text
View/download PDF

32. Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure: n-CdCr2Se4 / AlGaAs / GaAs

Author

Jonker, B. T., Hanbicki, A. T., Kioseoglou, G., Li, C. H., Stroud, R. M., Sullivan, J. M., Erwin, S. C., Lüpke, G., Zhao, H. B., Ren, Y. H., Sun, B., Itskos, Grigorios, Mallory, R., Yasar, M., Petrou, Athos Chariton, and Itskos, Grigorios [0000-0003-3971-3801]

Subjects
Magnetic semiconductors, Condensed Matter::Materials Science, Electroluminescence, Condensed Matter::Other, Spin injection, Heterojunctions, Ferromagnetism, Condensed Matter::Strongly Correlated Electrons, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Semiconducting zinc compounds
Abstract

The electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure were discussed. The electrical spin injection from spin-LED structures showed defect-dominated electroluminescence. The analysis showed that the addition of a ZnSe interlayer provides a smaller conduction band offset in CdCr2Se4/ZnSe/(AlGa)As heterostructure. Sponsors: Magnetics Society of the IEEE Conference code: 61560

Published
2003

33. Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure: n-CdCr2Se4/AlGaAs/GaAs

Author

Jonker, B. T., Hanbicki, A. T., Kioseoglou, G., Li, C. H., Stroud, R. M., Sullivan, J. M., Erwin, S. C., Lüpke, G., Zhao, H. B., Ren, Y. H., Sun, B., Itskos, Grigorios, Mallory, R., Yasar, M., Petrou, Athos Chariton, and Itskos, Grigorios [0000-0003-3971-3801]

Subjects
Spin polarization, Materials science, Ferromagnetic semiconductor, Gallium arsenide, Semiconducting selenium compounds, chemistry.chemical_compound, Condensed Matter::Materials Science, Condensed Matter::Superconductivity, Polarization, Band alignments, Band offsets, Spin polarized transport, Condensed matter physics, business.industry, Heterojunction, Magnetic semiconductor, Coercivity, Magnetic hysteresis, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Coercive field, Light emitting diodes, Aluminum gallium arsenide, Electrical spin injection, Magnetic anisotropy, Hysteresis, chemistry, Electroluminescence, Hysteresis behavior, Remanence, Heterojunctions, Ferromagnetism, Optoelectronics, Ferromagnetic materials, Epitaxially grown, business
Abstract

Electrical spin injection and band offsets in an n-type ferromagnetic semiconductor heterostructure of CdCr2Se4-AlGaAs-GaAs are studied. Epitaxially grown CdCr2Se4 films exhibit hysteresis behavior with significant remanence, an in- plane easy axis with a coercive field of 125 Oe. The cross section of the LED and the band alignment were shown. © 2003 IEEE. Sponsors: Magnetics Society of the Institute of Electrical and Electronics Engineers Conference code: 114081

Published
2003

Catalog

Books, media, physical & digital resources
See catalog results