Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization

We follow for the first time the evolution of the spin and orbital angular momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray magnetic circular dichroism. Both components decrease with a 130 +/- 40 fs time constant upon excitation with a femtosecond laser pulse. Additional x-ray absorption measurements reveal an increase in the spin-orbit interaction by 6 +/- 2 % during this process. This is the experimental demonstration quantifying the importance of spin-orbit mediated processes during the demagnetization

Laser pump X ray probe experiments with electrons ejected from a Cu 111 target space charge acceleration

A comprehensive investigation of the emission characteristics for electrons induced by X rays of a few hundred eV at grazing incidence angles on an atomically clean Cu 111 sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation high peak current of photoemission on the properties of Auger and photoelectrons liberated by a probe X ray beam is investigated in time resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical result

Distribution Of Foraging Shearwaters Relative To Inner Front Of SE Bering Sea

We examined the hypothesis that short-tailed shearwaters Puffinus tenuirostris aggregate to forage at the inner front of the SE Bering Sea because of enhanced production there. We tested this hypothesis by comparing primary production, the distribution of euphausiids and the distribution of shearwaters relative to the front during late spring and late summer/early fall of 1997, 1998 and 1999. We found enhanced primary production at the front and offshore of the front during summer but not during spring. Primary production varied between seasons and years. Major differences were related to anomalous conditions in 1997 and 1998. The density of euphausiids was higher at the front and offshore of the front during summer, but there were no differences among regions during spring. Foraging shearwaters aggregated in high densities at the front during summer, but foraged close to shore during spring. At the front, shearwaters foraged on euphausiids Thysanoessa raschii and T. inermis as expected, and on copepods that accumulated in the area. The proportion of zooplankton consumed at the front decreased from summer 1997 to summer 1999, while consumption of sandlance Ammodytes hexapterus at this feature increased. Our results show that, during summer, the inner front supports aggregations of euphausiids and their seabird predators. The means by which the frontal system supports enhanced production and the subsequent trophic transfers is dependent on the availability of nutrients at depth in the frontal region and the aggregation of small zooplankton organisms in this feature

Three interacting freshwater plumes in the northern California Current System

The northern California Current System is impacted by two primary freshwater sources: the Strait of Juan de Fuca and the Columbia River. The Columbia is frequently bidirectional in summer, with branches both north and south of the river mouth simultaneously. We describe the interaction of these two warm Columbia plumes with each other and with the colder plume originating from the strait. The interactions occurred when a period of strong downwelling-favorable winds and high Columbia River discharge was followed by persistent and strong upwelling-favorable winds. The northward plume that developed under the downwelling winds extended over 200 km along the coast to the Strait of Juan de Fuca and into the strait. The plume subsequently wrapped around Juan de Fuca Strait water in the counterclockwise seasonal eddy just offshore of the strait. Inspection for similar wind and outflow conditions (>0.15 N m¯² and 10⁴ m³ s¯¹, respectively) suggest that these events might have occurred in roughly half the years since 1994. Surface drifters deployed in the Columbia plume near its origin tracked this plume water northward along the coast, then reversed direction at the onset of upwelling-favorable winds, tracking plume water southward past the river mouth once again. ‘‘Recent’’ (~1–2 day old) and ‘‘Aged’’ (>14 day old) plume water folded around the newly emerging southwest tending Columbia plume, forming a distinctive ‘‘sock’’ shaped plume. This plume was a mixture of ~10% ‘‘New’’ (<1 day old) water and ~90% Recent and Aged water from prior north tending plumes

Ultrafast and Distinct Spin Dynamics in Magnetic Alloys

Controlling magnetic order on ultrashort timescales is crucial for engineering the next-generation magnetic devices that combine ultrafast data processing with ultrahigh-density data storage. An appealing scenario in this context is the use of femtosecond (fs) laser pulses as an ultrafast, external stimulus to fully set the orientation and the magnetization magnitude of a spin ensemble. Achieving such control on ultrashort timescales, e.g., comparable to the excitation event itself, remains however a challenge due to the lack of understanding the dynamical behavior of the key parameters governing magnetism: The elemental magnetic moments and the exchange interaction. Here, we investigate the fs laser-induced spin dynamics in a variety of multi-component alloys and reveal a dissimilar dynamics of the constituent magnetic moments on ultrashort timescales. Moreover, we show that such distinct dynamics is a general phenomenon that can be exploited to engineer new magnetic media with tailor-made, optimized dynamic properties. Using phenomenological considerations, atomistic modeling and time-resolved X-ray magnetic circular dichroism (XMCD), we demonstrate demagnetization of the constituent sub-lattices on significantly different timescales that depend on their magnetic moments and the sign of the exchange interaction. These results can be used as a “recipe” for manipulation and control of magnetization dynamics in a large class of magnetic materials

Two color synchrotron X ray spectroscopy based on transverse resonance island buckets

We report on a novel multi color method of X ray spectroscopy at a Synchrotron radiation source that uses two simultaneously filled electron orbits in an electron storage ring to generate multiple soft or tender X ray beams of different wavelength. To establish the second orbit, we use nonlinear beam dynamics in the so called TRIBs transverse resonance island buckets mode of the BESSY II storage ring, where a second electron orbit winds around the regular one leading to transversely separated source points. X ray beams of multiple colors are generated by imaging the individual source points via different pathways through a monochromator. The particular colors can be varied by changing the traversal electron beam positions through storage ring parameters and or via the monochromator dispersion. As a proof of principle, X ray absorption spectroscopy is performed on thin Fe films in transmission as well as a scanning transmission measurement on a Fe3GeTe2 sample of inhomogeneous thickness normalizing resonant signals with the pre edge intensity. Using the extraordinary pointing fidelity of successive X ray macro pulses arriving at MHz repetition rates, a detection of tiny contrasts in diluted systems, contrast enhancement in X ray microscopy as well as fast dynamics studies come into reac

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