@article{LiuRuotsalainenBaueretal.2022,
  author    = {Liu, Chun-Yu and Ruotsalainen, Kari and Bauer, Karl and Decker, R{\´e}gis and Pietzsch, Annette and F{\"o}hlisch, Alexander},
  title     = {Excited-state exchange interaction in NiO determined by high-resolution resonant inelastic x-ray scattering at the Ni M2,3 edges},
  series = {Physical review : B, Condensed matter and materials physics},
  volume    = {106},
  journal   = {Physical review : B, Condensed matter and materials physics},
  number    = {3},
  publisher = {American Physical Society},
  address   = {Ridge, NY},
  issn      = {2469-9950},
  doi       = {10.1103/PhysRevB.106.035104},
  pages     = {7},
  year      = {2022},
  abstract  = {The electronic and magnetic excitations of bulk NiO have been determined using the 3A2g to 3T2g crystal-field transition at the Ni M2,3 edges with resonant inelastic x-ray scattering at 66.3- and 67.9-eV photon energies and 33-meV spectral resolution. Unambiguous assignment of the high-energy side of this state to a spin-flip satellite is achieved. We extract an effective exchange field of 89±4 meV in the 3T2g excited final state from empirical two-peak spin-flip model. The experimental data is found consistent with crystal-field model calculations using exchange fields of 60-100 meV. Full agreement with crystal-field multiplet calculations is achieved for the incident photon energy dependence of line shapes. The lower exchange parameter in the excited state as compared to the ground-state value of 120 meV is discussed in terms of the modification of the orbital occupancy (electronic effects) and of the structural dynamics: (A) With pure electronic effects, the lower exchange energy is attributed to the reduction in effective hopping integral. (B) With no electronic effects, we use the S = 1 Heisenberg model of antiferromagnetism to derive a second-nearest-neighbor exchange constant J2 = 14.8±0.6 meV. Based on the linear correlation between J2 and the lattice parameter from pressure-dependent experiments, an upper limit of 2\% local Ni-O bond elongation during the femtosecond scattering duration is derived.},
  language  = {en}
}
@article{DeckerBornBuechneretal.2019,
  author    = {Decker, R{\´e}gis and Born, Artur and B{\"u}chner, Robby and Ruotsalainen, Kari and Str{\aa}hlman, Christian and Neppl, Stefan and Haverkamp, Robert and Pietzsch, Annette and F{\"o}hlisch, Alexander},
  title     = {Measuring the atomic spin-flip scattering rate by x-ray emission spectroscopy},
  series = {Scientific reports},
  volume    = {9},
  journal   = {Scientific reports},
  publisher = {Nature Publ. Group},
  address   = {London},
  issn      = {2045-2322},
  doi       = {10.1038/s41598-019-45242-8},
  pages     = {6},
  year      = {2019},
  abstract  = {While extensive work has been dedicated to the measurement of the demagnetization time following an ultra-short laser pulse, experimental studies of its underlying microscopic mechanisms are still scarce. In transition metal ferromagnets, one of the main mechanism is the spin-flip of conduction electrons driven by electron-phonon scattering. Here, we present an original experimental method to monitor the electron-phonon mediated spin-flip scattering rate in nickel through the stringent atomic symmetry selection rules of x-ray emission spectroscopy. Increasing the phonon population leads to a waning of the 3d -> 2p(3/2) decay peak intensity, which reflects an increase of the angular momentum transfer scattering rate attributed to spin-flip. We find a spin relaxation time scale in the order of 50 fs in the 3d-band of nickel at room temperature, while consistantly, no such peak evolution is observed for the diamagnetic counterexample copper, using the same method.},
  language  = {en}
}