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  • 1.
    Battiato, Marco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Barbalinardo, G.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Beyond linear response theory for intensive light-matter interactions: Order formalism and ultrafast transient dynamics2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 4, 045117- p.Article in journal (Refereed)
    Abstract [en]

    Recently constructed radiation sources deliver brilliant, ultrashort coherent radiation fields with which the material's response can be investigated on the femtosecond to attosecond time scale. Here, we develop a theoretical framework for the interaction of the material's electrons with such intensive, short radiation pulses. Our theory is based on the time evolution of the electron density matrix, as defined through the Liouville-von Neumann equation. The latter equation is solved here within the framework of the response theory, incorporating the perturbing field in higher orders. An analytical tool, called the order notation, is developed, which permits the explicit calculation of the arising nth-order operatorial convolutions. As examples of the formalism, explicit expressions for several optical phenomena are worked out. Through the developed theory presented here, two fundamental results are achieved: first, the perturbing field to higher than linear orders is included in an elegant and compact way, allowing to treat highly brilliant light, and, second, the complete transient time response on the subfemtosecond scale is analytically provided, thus dropping the adiabatic approximation commonly made in standard linear response theory.

  • 2.
    Battiato, Marco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theory of laser-induced ultrafast superdiffusive spin transport in layered heterostructures2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 2, 024404- p.Article in journal (Refereed)
    Abstract [en]

    Femtosecond laser excitation of a ferromagnetic material creates energetic spin-polarized electrons that have anomalous transport characteristics. We develop a semiclassical theory that is specifically dedicated to capture the transport of laser-excited nonequilibrium (NEQ) electrons. The randomly occurring multiple electronic collisions, which give rise to electron thermalization, are treated exactly and we include the generation of electron cascades due to inelastic electron-electron scatterings. The developed theory can, moreover, treat the presence of several different layers in the laser-irradiated material. The derived spin-dependent transport equation is solved numerically and it is shown that the hot NEQ electron spin transport occurs neither in the diffusive nor ballistic regime, it is superdiffusive. As the excited spin majority and minority electrons in typical transition-metal ferromagnets (e.g., Fe, Ni) have distinct, energy-dependent lifetimes, fast spin dynamics in the femtosecond (fs) regime is generated, causing effectively a spin current. As examples, we solve the resulting spin dynamics numerically for typical heterostructures, specifically, a ferromagnetic/nonmagnetic metallic layered junction (i.e., Fe/Al and Ni/Al) and a ferromagnetic/nonmagnetic insulator junction (Fe or Ni layer on a large band-gap insulator as, e.g., MgO). For the ferromagnetic/nonmagnetic metallic junction where the ferromagnetic layer is laser-excited, the computed spin dynamics shows that injection of a superdiffusive spin current in the nonmagnetic layer (Al) is achieved. The injected spin current consists of screened NEQ, mobile majority-spin electrons and is nearly 90% spin-polarized for Ni and about 65% for Fe. Concomitantly, a fast demagnetization of the ferromagnetic polarization in the femtosecond regime is driven. The analogy of the generated spin current to a superdiffusive spin Seebeck effect is surveyed.

  • 3.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ultrafast Spintronics: Give It A Whirl2014In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 10, no 8, 552-553 p.Article in journal (Other (popular science, discussion, etc.))
  • 4. Carva, Karel
    et al.
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Legut, D.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio theory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 18, 184425- p.Article in journal (Refereed)
    Abstract [en]

    We report a computational theoretical investigation of electron spin-flip scattering induced by the electron-phonon interaction in the transition-metal ferromagnets bcc Fe, fcc Co, and fcc Ni. The Elliott-Yafet electron-phonon spin-flip scattering is computed from first principles, employing a generalized spin-flip Eliashberg function as well as ab initio computed phonon dispersions. Aiming at investigating the amount of electron-phonon mediated demagnetization in femtosecond laser-excited ferromagnets, the formalism is extended to treat laser-created thermalized as well as nonequilibrium, nonthermal hot electron distributions. Using the developed formalism we compute the phonon-induced spin lifetimes of hot electrons in Fe, Co, and Ni. The electron-phonon mediated demagnetization rate is evaluated for laser-created thermalized and nonequilibrium electron distributions. Nonthermal distributions are found to lead to a stronger demagnetization rate than hot, thermalized distributions, yet their demagnetizing effect is not enough to explain the experimentally observed demagnetization occurring in the subpicosecond regime.

  • 5.
    Carva, Karel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Legut, Dominik
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theory of femtosecond laser-induced demagnetization2015In: ULTRAFAST MAGNETISM I, 2015, 111-115 p.Conference paper (Refereed)
    Abstract [en]

    Using ab initio calculations we computed the ultrafast demagnetization that can be achieved by Elliott-Yafet electron-phonon spin-flip scatterings in laser-excited ferromagnets. Our calculations show that nonequilibrium laser-created distributions contribute mostly to the ultrafast demagnetization. Nonetheless, the total Elliott-Yafet contribution is too small to account for the fs-demagnetization.

  • 6.
    Carva, Karel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Battiato, Marco
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab Initio Investigation of the Elliott-Yafet Electron-Phonon Mechanism in Laser-Induced Ultrafast Demagnetization2011In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, no 20, 207201- p.Article in journal (Refereed)
    Abstract [en]

    The spin-flip (SF) Eliashberg function is calculated from first principles for ferromagnetic Ni to accurately establish the contribution of Elliott-Yafet electron-phonon SF scattering to Ni's femtosecond laser-driven demagnetization. This is used to compute the SF probability and demagnetization rate for laser-created thermalized as well as nonequilibrium electron distributions. Increased SF probabilities are found for thermalized electrons, but the induced demagnetization rate is extremely small. A larger demagnetization rate is obtained for nonequilibrium electron distributions, but its contribution is too small to account for femtosecond demagnetization.

  • 7.
    Fan, T.
    et al.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Grychtol, P.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Knut, R.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Hernandez-Garcia, C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA.;Univ Salamanca, Grp Invest Opt Extrema, E-37008 Salamanca, Spain..
    Hickstein, D. D.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Zusin, D.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Gentry, C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Dollar, F. J.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Mancuso, C. A.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Hogle, C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Kfir, O.
    Technion, Inst Solid State, IL-32000 Haifa, Israel.;Technion, Dept Phys, IL-32000 Haifa, Israel..
    Legut, D.
    VSB Tech Univ Ostrava, Ctr IT4Innovat, 17 Listopadu 15, CZ-70833 Ostrava, Czech Republic.;Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu, Czech Republic..
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu, Czech Republic..
    Ellis, J. L.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Dorney, K.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Chen, C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Shpyrko, O.
    Univ Calif San Diego, Dept Phys, La Jolla, CA 92093 USA..
    Fullerton, E. E.
    Univ Calif San Diego, Ctr Magnet Recording Res, La Jolla, CA 92093 USA..
    Cohen, O.
    Technion, Inst Solid State, IL-32000 Haifa, Israel.;Technion, Dept Phys, IL-32000 Haifa, Israel..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Milosevic, D. B.
    Univ Sarajevo, Fac Sci, Zmaja Bosne 35, Sarajevo 71000, Bosnia & Herceg.;Acad Sci & Arts Bosnia & Herzegovina, Bistrik 7, Sarajevo 71000, Bosnia & Herceg.;Max Born Inst, Max Born Str 2a, D-12489 Berlin, Germany..
    Becker, A.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Jaron-Becker, A. A.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Popmintchev, T.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Kapteyn, H. C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Murnane, M. M.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Generation of Bright Soft X-ray Harmonics with Circular Polarization for X-ray Magnetic Circular Dichroism2016In: 2016 Conference On Lasers And Electro-Optics (CLEO), 2016Conference paper (Refereed)
    Abstract [en]

    We present the first circularly polarized harmonics in the soft X-ray region and the physics underlying it. This source enables the first X-ray magnetic circular dichroism measurements in rare earth elements on tabletop.

  • 8.
    Fan, Tingting
    et al.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Grychtol, Patrik
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Knut, Ronny
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Hernandez-Garcia, Carlos
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Salamanca, Grp Invest Opt Extrema, E-37008 Salamanca, Spain..
    Hickstein, Daniel D.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Zusin, Dmitriy
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Gentry, Christian
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Dollar, Franklin J.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Mancuso, Christopher A.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Hogle, Craig W.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Kfir, Ofer
    Technion Israel Inst Technol, Solid State Inst & Phys Dept, IL-32000 Haifa, Israel..
    Legut, Dominik
    Tech Univ Ostrava, Ctr DIT4Innovat, CZ-70833 Ostrava, Czech Republic.;Charles Univ Prague, Dept Condensed Matter Phys, Fac Math & Phys, CZ-12116 Prague 2, Czech Republic..
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Charles Univ Prague, Dept Condensed Matter Phys, Fac Math & Phys, CZ-12116 Prague 2, Czech Republic..
    Ellis, Jennifer L.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Dorney, Kevin M.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Chen, Cong
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Shpyrko, Oleg G.
    Univ Calif San Diego, Dept Phys, La Jolla, CA 92093 USA..
    Fullerton, Eric E.
    Univ Calif San Diego, Ctr Magnet Recording Res, La Jolla, CA 92093 USA..
    Cohen, Oren
    Technion Israel Inst Technol, Solid State Inst & Phys Dept, IL-32000 Haifa, Israel..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Milosevic, Dejan B.
    Univ Sarajevo, Fac Sci, Sarajevo 71000, Bosnia & Herceg.;Acad Sci & Arts Bosnia & Herzegovina, Sarajevo 71000, Bosnia & Herceg.;Max Born Inst, D-12489 Berlin, Germany..
    Becker, Andreas
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Jaron-Becker, Agnieszka A.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Popmintchev, Tenio
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Murnane, Margaret M.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Kapteyn, Henry C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA..
    Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism2015In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, no 46, 14206-14211 p.Article in journal (Refereed)
    Abstract [en]

    We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 mu m, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N-4,N-5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.

  • 9.
    Frietsch, B.
    et al.
    Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany.;Max Born Inst, D-12489 Berlin, Germany..
    Bowlan, J.
    Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany.;Max Born Inst, D-12489 Berlin, Germany..
    Carley, R.
    Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany.;Max Born Inst, D-12489 Berlin, Germany..
    Teichmann, M.
    Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany.;Max Born Inst, D-12489 Berlin, Germany..
    Wienholdt, S.
    Univ Konstanz, Fachbereich Phys, D-78457 Constance, Germany..
    Hinzke, D.
    Univ Konstanz, Fachbereich Phys, D-78457 Constance, Germany..
    Nowak, U.
    Univ Konstanz, Fachbereich Phys, D-78457 Constance, Germany..
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Charles Univ Prague, Fac Math & Phys, DCMP, CZ-12116 Prague 2, Czech Republic..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Weinelt, M.
    Free Univ Berlin, Fachbereich Phys, D-14195 Berlin, Germany..
    Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, 8262Article in journal (Refereed)
    Abstract [en]

    The Heisenberg-Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale.

  • 10.
    Hinzke, D.
    et al.
    Univ Konstanz, Fachbereich Phys, Constance, Germany..
    Atxitia, U.
    Univ Konstanz, Fachbereich Phys, Constance, Germany.;Univ Konstanz, Zukunftskolleg, Constance, Germany..
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Charles Univ Prague, DCMP, Fac Math & Phys, Prague, Czech Republic..
    Nieves, P.
    CSIC, Inst Ciencia Mat Madrid, Madrid, Spain..
    Chubykalo-Fesenko, O.
    CSIC, Inst Ciencia Mat Madrid, Madrid, Spain..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nowak, U.
    Univ Konstanz, Fachbereich Phys, Constance, Germany..
    Multiscale modeling of ultrafast element- specific magnetization dynamics in FeNi ferromagnetic alloys2015In: 2015 IEEE Magnetics Conference (INTERMAG), 2015Conference paper (Other academic)
  • 11. Hinzke, D.
    et al.
    Atxitia, U.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nieves, P.
    Chubykalo-Fesenko, O.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nowak, U.
    Multiscale modeling of ultrafast element-specific magnetization dynamics of ferromagnetic alloys2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 5, 054412Article in journal (Refereed)
    Abstract [en]

    A hierarchical multiscale approach to model the magnetization dynamics of ferromagnetic random alloys is presented. First-principles calculations of the Heisenberg exchange integrals are linked to atomistic spin models based upon the stochastic Landau-Lifshitz-Gilbert (LLG) equation to calculate temperature-dependent parameters (e.g., effective exchange interactions, damping parameters). These parameters are subsequently used in the Landau-Lifshitz-Bloch (LLB) model for multisublattice magnets to calculate numerically and analytically the ultrafast demagnetization times. The developed multiscale method is applied here to FeNi (permalloy) as well as to copper-doped FeNi alloys. We find that after an ultrafast heat pulse the Ni sublattice demagnetizes faster than the Fe sublattice for the here-studied FeNi-based alloys.

  • 12.
    Mondal, Ritwik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Berritta, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio investigation of light-induced relativistic spin-flip effects in magneto-optics2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 17, 174415Article in journal (Refereed)
    Abstract [en]

    Excitation of a metallic ferromagnet such as Ni with an intensive femtosecond laser pulse causes an ultrafast demagnetization within approximately 300 fs. It was proposed that the ultrafast demagnetization measured in femtosecond magneto-optical experiments could be due to relativistic light-induced processes. We perform an ab initio investigation of the influence of relativistic effects on the magneto-optical response of Ni. To this end, first, we develop a response theory formulation of the additional appearing ultrarelativistic terms in the Foldy-Wouthuysen transformed Dirac Hamiltonian due to the electromagnetic field, and second, we compute the influence of relativistic light-induced spin-flip transitions on the magneto-optics. Our ab initio calculations of relativistic spin-flip optical excitations predict that these can give only a very small contribution (<= 0.1%) to the laser-induced magnetization change in Ni.

  • 13. Wienholdt, S.
    et al.
    Hinzke, D.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Nowak, U.
    Orbital-resolved spin model for thermal magnetization switching in rare-earth-based ferrimagnets2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 2, 020406- p.Article in journal (Refereed)
    Abstract [en]

    The switching of rare-earth-based ferrimagnets triggered by thermal excitation is investigated on the basis of an atomistic spin model beyond the rigid-spin approximation, distinguishing magnetic moments due to electrons in d and f orbitals of the rare earth. It is shown that after excitation of the conduction electrons a transient ferromagneticlike state follows from a dissipationless spin dynamics where energy and angular momentum are distributed between the two sublattices. The final relaxation can then lead to a new state with the magnetization switched with respect to the initial state. The time scale of the switching event is to a large extent determined by the exchange interaction between the two sublattices.

1 - 13 of 13
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