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Structural dynamics 8(3), 034305 (1-9) (2021). doi:10.1063/4.0000109, During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump–probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm (≃310 eV), we were able to probe close to the Fe $L_3$ edge (706.8 eV) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization, Published by AIP Publishing LLC, Melville, NY

Ultrashort optical pulses can trigger a variety of non-equilibrium processes in magnetic thin films affecting electrons and spins on femtosecond timescales. In order to probe the charge and magnetic degrees of freedom simultaneously, we developed an X-ray streaking technique that has the advantage of providing a jitter-free picture of absorption cross-section changes. In this paper, we present an experiment based on this approach, which we performed using five photon probing energies at the Ni M2,3-edges. This allowed us to retrieve the absorption and magnetic circular dichroism time traces, yielding detailed information on transient modifications of electron and spin populations close to the Fermi level. Our findings suggest that the observed absorption and magnetic circular dichroism dynamics both depend on the extreme ultraviolet (XUV) probing wavelength, and can be described, at least qualitatively, by assuming ultrafast energy shifts of the electronic and magnetic elemental absorption resonances, as reported in recent work. However, our analysis also hints at more complex changes, highlighting the need for further experimental and theoretical studies in order to gain a thorough understanding of the interplay of electronic and spin degrees of freedom in optically excited magnetic thin films.

We present a detailed experimental-theoretical analysis of O K-edge resonant 1 sigma-2 pi inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high ...

The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12–14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of “dark” with “bright” final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.

X-ray photoelectron spectroscopy (XPS), magnetization and magnetic susceptibility of Gd 3 Ni 8 Al are reported. Both valence band and core level spectra were analyzed. Ni atoms have no magnetic moment because of charge transfer of Gd conduction electrons to the 3d band. This effect is mainly related with the 6s electrons of Gd. The filling of the Ni 3d band is revealed by the density of states at the Fermi level, the chemical shifts of Gd and Ni core levels and the value of the effective magnetic moment in the paramagnetic state. The compound Gd 3 Ni 8 Al exhibits a collinear ferromagnetic arrangement of Gd moments below the Curie temperature T C =61 K. A negative 3d band polarization of 0.15 μ B /Ni is induced by the exchange interactions with the Gd spins.

X-ray photoelectron spectroscopy (XPS), magnetization and magnetic susceptibility of Gd 3 Ni 8 Al are reported. Both valence band and core level spectra were analyzed. Ni atoms have no magnetic moment because of charge transfer of Gd conduction electrons to the 3d band. This effect is mainly related with the 6s electrons of Gd. The filling of the Ni 3d band is revealed by the density of states at the Fermi level, the chemical shifts of Gd and Ni core levels and the value of the effective magnetic moment in the paramagnetic state. The compound Gd 3 Ni 8 Al exhibits a collinear ferromagnetic arrangement of Gd moments below the Curie temperature T C =61 K. A negative 3d band polarization of 0.15 μ B /Ni is induced by the exchange interactions with the Gd spins.

The high-T(c) superconductor Tl(2)Ba(2)CuO(6 + delta) is studied by angle-resolved photoemission spectroscopy. For a very overdoped T(c) = 30 K sample, the Fermi surface consists of a single large hole pocket centered at (pi, pi) and is approaching a topological transition. Although a superconducting gap with d(x(2)-y(2)) symmetry is tentatively identified, the quasiparticle evolution with momentum and binding energy exhibits a marked departure from the behavior observed in under and optimally doped cuprates. The relevance of these findings to scattering, many-body, and quantum-critical phenomena is discussed.