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We report the first analysis of the polarization and lattice dynamics in a metal/ferroelectric/metal nanolayer system by femtosecond x-ray diffraction. Two Bragg reflections provide information on the coupled dynamics of the two relevant phonon modes for ferroelectricity in perovskites, the tetragonal distortion and the soft mode. Optical excitation of the SrRuO(3) metal layers generates giant stress (>1 GPa) compressing the PbZr(0.2)Ti(0.8)O(3) layers by up to 2%. The resulting change of tetragonality reaches a maximum after 1.3 ps. As a result, the ferroelectric polarization P is reduced by up to 100% with a slight delay that is due to the anharmonic coupling of the two modes.

Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate this, we perform a joint theoretical and experimental investigation to determine the transient changes of the helicity dependent absorption in the extreme ultraviolet spectral range. We show that the helicity dependent absorption is directly related to changes of the transient spin-split density of states, allowing us to link the origin of OISTR to the available minority states above the Fermi level. This makes OISTR a general phenomenon in optical manipulation of multi-component magnetic systems.

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Magnetic circular dichroism in the extreme ultraviolet (XUV) spectral range is a powerful technique for element-specific probing of magnetization in multicomponent magnetic alloys and multilayers. We combine a high-harmonic generation source with a λ/4 phase shifter to obtain circularly polarized XUV femtosecond pulses for ultrafast magnetization studies. We report on simultaneously measured resonant magnetic circular dichroism (MCD) of Co and Ni at their respective M 2,3 edges and of Pt at its O edge, originating from interface magnetism. We present a time-resolved MCD absorption measurement of a thin magnetic Pt/Co/Pt film, showing simultaneous demagnetization of Co and Pt on a femtosecond time scale.

The udkm1Dsim toolbox is a collection of matlab (MathWorks Inc.) classes and routines to simulate the structural dynamics and the according X-ray diffraction response in one-dimensional crystalline sample structures upon an arbitrary time-dependent external stimulus, e.g. an ultrashort laser pulse. The toolbox provides the capabilities to define arbitrary layered structures on the atomic level including a rich database of corresponding element-specific physical properties. The excitation of ultrafast dynamics is represented by an N -temperature model which is commonly applied for ultrafast optical excitations. Structural dynamics due to thermal stress are calculated by a linear-chain model of masses and springs. The resulting X-ray diffraction response is computed by dynamical X-ray theory. The udkm1Dsim toolbox is highly modular and allows for introducing user-defined results at any step in the simulation procedure.

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Ultrashort, coherent x-ray pulses of a free-electron laser are used to holographically image the magnetization dynamics within a magnetic domain pattern after creation of a localized excitation via an optical standing wave. We observe a spatially confined reduction of the magnetization within a couple of hundred femtoseconds followed by its slower recovery. Additionally, the experimental results show evidence of a spatial evolution of magnetization, which we attribute to ultrafast transport of nonequilibrium spin-polarized electrons for early times and to a fluence-dependent remagnetization rate for later times. DOI: 10.1103/PhysRevLett.112.217203 PACS numbers: 75.78.Jp, 42.40.Kw, 75.25.−j, 78.70.Ck Progress in the field of light-induced, ultrafast manipulation of magnetic order has recently led to all-optical, ultrafast magnetic switching [1][2][3] and to an increased control of its dynamics by designing tailored nanostructured samples [4][5][6][7] as well as by exploiting nanoscale magnetic inhomogeneities [8,9]. The influence of interfaces between different materials and magnetic domain boundaries has cast doubt on our theoretical understanding of the underlying fundamental mechanism responsible for femtosecond magnetization dynamics. The model explaining the ultrafast loss of magnetic order after optical excitation by (e.g., electron-phonon or impurity-mediated) spin-flip scattering events [10] has in part been challenged by an approach based on nonlocal superdiffusive spin transport [11]. In spite of their very different microscopic origins, both have been successful in explaining a wide range of experimental data, suggesting that both mechanisms play an important role and that their respective magnitudes depend on the specific experimental conditions [7]. More specifically, in the case of superdiffusive spin transport, energy-and spin-dependent electron lifetimes and velocities induce spin-polarized currents, leading to significant ultrafast spatial rearrangement of magnetic order.To gain control of magnetization dynamics and all-optical switching in the lateral dimension, one relies on nanometer localization of the optical excitation, as well as detailed knowledge on how (spin-polarized) electron currents lead to a spatial transfer of magnetization. Technologically this plays an important role not only for all-optical approaches, but also for heat-assisted magnetic recording, which has the potential to increase the magnetic recording density by lowering the coercitivity of high-anisotropy materials [12]. Necessary to this end, it is required to deliver the optical energy to a sub-100-nm spot size, i.e., far beyond the diffraction limit of optical light. The most successful approaches include localization of the evanescent light from near-field optical probes [13], using metallic plates to excite surface plasmons [14,15] or a combination thereof [16].Here, we implement time-resolved Fourier transform holography (FTH) [17] and exploit x-ray magnetic circular dichroism (XMCD) to directly image the magnet...