Spin Flips versus Spin Transport in Nonthermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals.

A joint theoretical and experimental investigation is performed to understand the underlying physics of laser-induced demagnetization in Ni and Co films with varying thicknesses excited by 10 fs optical pulses. Experimentally, the dynamics of spins is studied by determining the time-dependent amplitude of the Voigt vector, retrieved from a full set of magnetic and nonmagnetic quantities performed on both sides of films, with absolute time reference. Theoretically, ab initio calculations are performed using time-dependent density functional theory. Overall, we demonstrate that spin-orbit induced spin flips are the most significant contributors with superdiffusive spin transport, which assumes only that the transport of majority spins without spin flips induced by scattering does not apply in Ni. In Co it plays a significant role during the first ∼20  fs only. Our study highlights the material dependent nature of the demagnetization during the process of thermalization of nonequilibrium spins.

[1]  E. Gross,et al.  Ultrafast laser induced local magnetization dynamics in Heusler compounds , 2016, Scientific Reports.

[2]  S. Sharma,et al.  An efficient algorithm for time propagation as applied to linearized augmented plane wave method , 2016, Comput. Phys. Commun..

[3]  M. Münzenberg,et al.  Perspective: Ultrafast magnetism and THz spintronics , 2016, 1606.08725.

[4]  E K U Gross,et al.  Laser-induced demagnetization at ultrashort time scales: predictions of TDDFT. , 2015, Journal of chemical theory and computation.

[5]  Y. Fainman,et al.  All-optical control of ferromagnetic thin films and nanostructures , 2014, Science.

[6]  B. Koopmans,et al.  Investigating the contribution of superdiffusive transport to ultrafast demagnetization of ferromagnetic thin films , 2013 .

[7]  D. Legut,et al.  Ab initio theory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets , 2013, 1305.3511.

[8]  A. Föhlisch,et al.  Ultrafast spin transport as key to femtosecond demagnetization. , 2013, Nature materials.

[9]  Andrei Kirilyuk,et al.  Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys , 2013, Reports on progress in physics. Physical Society.

[10]  M. Battiato,et al.  Theory of laser-induced ultrafast superdiffusive spin transport in layered heterostructures , 2012 .

[11]  J. Bigot,et al.  Ultrafast spin-photon interaction investigated with coherent magneto-optics , 2012 .

[12]  P. Zeitoun,et al.  Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network , 2012, Nature Communications.

[13]  M. Battiato,et al.  Superdiffusive spin transport as a mechanism of ultrafast demagnetization. , 2010, Physical review letters.

[14]  J. Bigot,et al.  Distinguishing the ultrafast dynamics of spin and orbital moments in solids , 2010, Nature.

[15]  M. Cinchetti,et al.  Explaining the paradoxical diversity of ultrafast laser-induced demagnetization. , 2010, Nature materials.

[16]  Martin Aeschlimann,et al.  Ultrafast demagnetization dynamics at the M edges of magnetic elements observed using a tabletop high-harmonic soft x-ray source. , 2009, Physical review letters.

[17]  J. Bigot,et al.  Coherent ultrafast magnetism induced by femtosecond laser pulses , 2009 .

[18]  C. Back,et al.  Laser-induced magnetization dynamics of lanthanide-doped permalloy thin films. , 2009, Physical Review Letters.

[19]  W. Eberhardt,et al.  Femtosecond modification of electron localization and transfer of angular momentum in nickel. , 2007, Nature materials.

[20]  V. Zhukov,et al.  Lifetimes and inelastic mean free path of low-energy excited electrons in Fe, Ni, Pt, and Au: Ab initio GW+T calculations , 2006 .

[21]  B. Koopmans,et al.  Unifying ultrafast magnetization dynamics. , 2005, Physical review letters.

[22]  Markus Donath,et al.  Spin-dependent electron dynamics in front of a ferromagnetic surface. , 2005, Physical review letters.

[23]  T. Rasing,et al.  Femtosecond photomagnetic switching of spins in ferrimagnetic garnet films. , 2005, Physical review letters.

[24]  R. Pisarev,et al.  Ultrafast non-thermal control of magnetization by instantaneous photomagnetic pulses , 2005, Nature.

[25]  P. Oppeneer,et al.  Ultrafast demagnetization in Ni: theory of magneto-optics for non-equilibrium electron distributions , 2004 .

[26]  H. Dürr,et al.  Femtosecond electron and spin dynamics in Ni/W(110) films. , 2003, Physical review letters.

[27]  G. P. Zhang,et al.  Laser-induced ultrafast demagnetization in ferromagnetic metals. , 2000, Physical review letters.

[28]  Michael Bauer,et al.  ULTRAFAST SPIN-DEPENDENT ELECTRON DYNAMICS IN FCC CO , 1997 .

[29]  K. Bennemann,et al.  NONEQUILIBRIUM MAGNETIZATION DYNAMICS OF NICKEL , 1997, cond-mat/9707078.

[30]  Merle,et al.  Ultrafast spin dynamics in ferromagnetic nickel. , 1996, Physical review letters.

[31]  J. Zak,et al.  Universal approach to magneto-optics , 1990 .

[32]  E. Gross,et al.  Density-Functional Theory for Time-Dependent Systems , 1984 .

[33]  C. C. Robinson.  Electromagnetic Theory of the Kerr and the Faraday Effects for Oblique Incidence , 1964 .

[34]  P. Hohenberg,et al.  Inhomogeneous Electron Gas , 1964 .

[35]  Alfred Leitenstorfer,et al.  Coherent terahertz control of antiferromagnetic spin waves , 2011 .