| 1. |
- Chen, Cong, et al.
(author)
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Distinguishing attosecond electron-electron scattering and screening in transition metals
- 2017
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In: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 114:27, s. E5300-E5307
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Journal article (peer-reviewed)abstract
- Electron-electron interactions are the fastest processes in materials, occurring on femtosecond to attosecond timescales, depending on the electronic band structure of the material and the excitation energy. Such interactions can play a dominant role in light-induced processes such as nano-enhanced plasmonics and catalysis, light harvesting, or phase transitions. However, to date it has not been possible to experimentally distinguish fundamental electron interactions such as scattering and screening. Here, we use sequences of attosecond pulses to directly measure electron-electron interactions in different bands of different materials with both simple and complex Fermi surfaces. By extracting the time delays associated with photoemission we show that the lifetime of photoelectrons from the d band of Cu are longer by similar to 100 as compared with those from the same band of Ni. We attribute this to the enhanced electron-electron scattering in the unfilled d band of Ni. Using theoretical modeling, we can extract the contributions of electron-electron scattering and screening in different bands of different materials with both simple and complex Fermi surfaces. Our results also show that screening influences high-energy photoelectrons (approximate to 20 eV) significantly less than low-energy photoelectrons. As a result, high-energy photoelectrons can serve as a direct probe of spin-dependent electron-electron scattering by neglecting screening. This can then be applied to quantifying the contribution of electron interactions and screening to low-energy excitations near the Fermi level. The information derived here provides valuable and unique information for a host of quantum materials.
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| 2. |
- Rollinger, Markus, et al.
(author)
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Light Localization and Magneto-Optic Enhancement in Ni Antidot Arrays
- 2016
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In: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 16:4, s. 2432-2438
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Journal article (other academic/artistic)abstract
- We reveal an explicit strategy to design the magneto-optic response of a magneto-plasmonic crystal by correlating near- and far-fields effects. We use photoemission electron microscopy to map the spatial distribution of the electric near-field on a nanopatterned magnetic surface that supports plasmon polaritons. By using different photon energies and polarization states of the incident light we reveal that the electric near-field is either concentrated in spots forming a hexagonal lattice with the same symmetry as the Ni nanopattern or in stripes oriented along the Gamma-K direction of the lattice and perpendicular to the polarization direction. We show that the polarization-dependent near-field enhancement on the patterned surface is directly correlated to both the excitation of surface plasmon polaritons on the patterned surface as well as the enhancement of the polar magneto-optical Kerr effect. We obtain a relationship between the size of the enhanced magneto optical behavior and the polarization and wavelength of optical excitation. The engineering of the magneto-optic response based on the plasmon-induced modification of the optical properties introduces the concept of a magneto-plasmonic meta-structure.
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| 3. |
- Stiehl, Martin, et al.
(author)
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All-optical switching in Cr- and Mn-doped L10 FePt thin films
- 2024
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In: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 21:5
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Journal article (peer-reviewed)abstract
- Optical manipulation of the magnetization of thin films opens up exciting possibilities for ever-faster magnetic storage applications. In this context, ?10 chemically ordered FePt thin films are of particular interest due to their high perpendicular magnetic anisotropy and their use as a storage material for heat-assisted magnetic recording devices. However, these materials are difficult to manipulate with external fields due to their high coercivity field. Thus, we want to explore the possibility of tailoring the properties of these materials to enable switching using all-optical techniques. While stochastic all-optical switching between partially magnetized states has been reported for undoped FePt thin films, we have investigated to what extent doping with third elements can influence the switching behavior. Reducing the saturation magnetization may be one way to facilitate all-optical switching. While this is expected with the introduction of additional elements, we also want to highlight the role of the inverse Faraday effect and the magnetic circular dichroism in stochastic all-optical switching. In this study, Cr was found to be a promising dopant, which can almost double the relative magnetization change of the partially magnetized states compared to pure FePt.
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| 4. |
- Rudolf, Dennis, et al.
(author)
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Element Selective Investigation of Spin Dynamics in Magnetic Multilayers
- 2015
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In: Ultrafast Magnetism I. - Cham : Springer International Publishing. - 9783319077437 - 9783319077420 ; , s. 307-309
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Conference paper (peer-reviewed)abstract
- Our understanding of ultrafast switching processes in novel spin-based electronics depends on our detailed knowledge of interactions between spin, charge and phonons in magnetic structures. We present element-selective studies, using extreme ultraviolet (XUV) light, to gain insight into spin dynamics in exchange coupled magnetic multilayers on the femtosecond time scale.
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| 5. |
- Rudolf, Dennis, et al.
(author)
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Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current
- 2012
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 3, s. 1037-
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Journal article (peer-reviewed)abstract
- Uncovering the physical mechanisms that govern ultrafast charge and spin dynamics is crucial for understanding correlated matter as well as the fundamental limits of ultrafast spin-based electronics. Spin dynamics in magnetic materials can be driven by ultrashort light pulses, resulting in a transient drop in magnetization within a few hundred femtoseconds. However, a full understanding of femtosecond spin dynamics remains elusive. Here we spatially separate the spin dynamics using Ni/Ru/Fe magnetic trilayers, where the Ni and Fe layers can be ferroor antiferromagnetically coupled. By exciting the layers with a laser pulse and probing the magnetization response simultaneously but separately in Ni and Fe, we surprisingly find that optically induced demagnetization of the Ni layer transiently enhances the magnetization of the Fe layer when the two layer magnetizations are initially aligned parallel. Our observations are explained by a laser-generated superdiffusive spin current between the layers.
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| 6. |
- Tengdin, Phoebe, et al.
(author)
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Direct light–induced spin transfer between different elements in a spintronic Heusler material via femtosecond laser excitation
- 2020
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In: Science Advances. - : American Association for the Advancement of Science. - 2375-2548. ; 6:3
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Journal article (peer-reviewed)abstract
- Heusler compounds are exciting materials for future spintronics applications because they display a wide range of tunable electronic and magnetic interactions. Here, we use a femtosecond laser to directly transfer spin polarization from one element to another in a half-metallic Heusler material, Co2MnGe. This spin transfer initiates as soon as light is incident on the material, demonstrating spatial transfer of angular momentum between neighboring atomic sites on time scales < 10 fs. Using ultrafast high harmonic pulses to simultaneously and independently probe the magnetic state of two elements during laser excitation, we find that the magnetization of Co is enhanced, while that of Mn rapidly quenches. Density functional theory calculations show that the optical excitation directly transfers spin from one magnetic sublattice to another through preferred spin-polarized excitation pathways. This direct manipulation of spins via light provides a path toward spintronic devices that can operate on few-femtosecond or faster time scales.
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| 7. |
- Turgut, Emrah, et al.
(author)
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Stoner versus Heisenberg : Ultrafast exchange reduction and magnon generation during laser-induced demagnetization
- 2016
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In: PHYSICAL REVIEW B. - 2469-9950. ; 94:22
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Journal article (peer-reviewed)abstract
- Understanding how the electronic band structure of a ferromagnetic material is modified during laser-induced demagnetization on femtosecond time scales has been a long-standing question in condensed matter physics. Here, we use ultrafast high harmonics to measure time-, energy-, and angle-resolved M-edge magnetic asymmetry spectra for Co films after optical pumping to induce ultrafast demagnetization. This provides a complete data set that we can compare with advanced ab initio magneto-optical calculations. Our analysis identifies that the dominant mechanisms contributing to ultrafast demagnetization on time scales up to several picoseconds are a transient reduction in the exchange splitting and the excitation of ultrafast magnons. Surprisingly, we find that the magnon contribution to ultrafast demagnetization is already strong on subpicosecond time scales, while the reduction in exchange splitting persists to several picoseconds.
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| 8. |
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