54 research outputs found
Irreversible transformation of ferromagnetic ordered stripe domains in single-shot IR pump - resonant X-ray scattering probe experiments
The evolution of a magnetic domain structure upon excitation by an intense,
femtosecond Infra-Red (IR) laser pulse has been investigated using single-shot
based time-resolved resonant X-ray scattering at the X-ray Free Electron laser
LCLS. A well-ordered stripe domain pattern as present in a thin CoPd alloy film
has been used as prototype magnetic domain structure for this study. The
fluence of the IR laser pump pulse was sufficient to lead to an almost complete
quenching of the magnetization within the ultrafast demagnetization process
taking place within the first few hundreds of femtoseconds following the IR
laser pump pulse excitation. On longer time scales this excitation gave rise to
subsequent irreversible transformations of the magnetic domain structure. Under
our specific experimental conditions, it took about 2 nanoseconds before the
magnetization started to recover. After about 5 nanoseconds the previously
ordered stripe domain structure had evolved into a disordered labyrinth domain
structure. Surprisingly, we observe after about 7 nanoseconds the occurrence of
a partially ordered stripe domain structure reoriented into a novel direction.
It is this domain structure in which the sample's magnetization stabilizes as
revealed by scattering patterns recorded long after the initial pump-probe
cycle. Using micro-magnetic simulations we can explain this observation based
on changes of the magnetic anisotropy going along with heat dissipation in the
film.Comment: 16 pages, 6 figure
Orbital dynamics during an ultrafast insulator to metal transition
Phase transitions driven by ultrashort laser pulses have attracted interest
both for understanding the fundamental physics of phase transitions and for
potential new data storage or device applications. In many cases these
transitions involve transient states that are different from those seen in
equilibrium. To understand the microscopic properties of these states, it is
useful to develop elementally selective probing techniques that operate in the
time domain. Here we show fs-time-resolved measurements of V Ledge Resonant
Inelastic X-Ray Scattering (RIXS) from the insulating phase of the Mott-
Hubbard material V2O3 after ultrafast laser excitation. The probed orbital
excitations within the d-shell of the V ion show a sub-ps time response, which
evolve at later times to a state that appears electronically indistinguishable
from the high-temperature metallic state. Our results demonstrate the potential
for RIXS spectroscopy to study the ultrafast orbital dynamics in strongly
correlated materials.Comment: 12 pages, 4 figure
Ultrafast domain dilation induced by optical pumping in ferromagnetic CoFe/Ni multilayers
Ultrafast optical pumping of systems with spatially nonuniform magnetic
textures is known to cause far-from-equilibrium spin transport effects, such as
the broadening of domain-walls. Here, we study the dynamics of labyrinth domain
networks in ferromagnetic CoFe/Ni multilayers subject to a femtosecond optical
pump and find an ultrafast domain dilation by 6% within 1.6 ps. This surprising
result is based on the unambiguous determination of a harmonically-related
shift of ultrafast magnetic X-ray diffraction for the first- and third-order
rings. Domain dilation is plausible from conservation of momentum arguments,
whereby inelastic scattering from a hot, quasi-ballistic, radial current
transfers momentum to the magnetic domains. Our results suggest a potentially
rich variety of unexpected physical phenomena associated with
far-from-equilibrium inelastic electron-magnon scattering processes in the
presence of spin textures
The Time-resolved Atomic, Molecular and Optical Science Instrument at the Linac Coherent Light Source
The newly constructed Time-resolved atomic, Molecular and Optical science
instrument (TMO), is configured to take full advantage of both linear
accelerators at SLAC National Accelerator Laboratory, the copper accelerator
operating at a repetition rate of 120 Hz providing high per pulse energy, as
well as the superconducting accelerator operating at a repetition rate of about
1 MHz providing high average intensity. Both accelerators build a soft X-ray
free electron laser with the new variable gab undulator section. With this
flexible light sources, TMO supports many experimental techniques not
previously available at LCLS and will have two X-ray beam focus spots in line.
Thereby, TMO supports Atomic, Molecular and Optical (AMO), strong-field and
nonlinear science and will host a designated new dynamic reaction microscope
with a sub-micron X-ray focus spot. The flexible instrument design is optimized
for studying ultrafast electronic and molecular phenomena and can take full
advantage of the sub-femtosecond soft X-ray pulse generation program
Photon shot-noise limited transient absorption soft X-ray spectroscopy at the European XFEL
Femtosecond transient soft X-ray Absorption Spectroscopy (XAS) is a very
promising technique that can be employed at X-ray Free Electron Lasers (FELs)
to investigate out-of-equilibrium dynamics for material and energy research.
Here we present a dedicated setup for soft X-rays available at the Spectroscopy
& Coherent Scattering (SCS) instrument at the European X-ray Free Electron
Laser (EuXFEL). It consists of a beam-splitting off-axis zone plate (BOZ) used
in transmission to create three copies of the incoming beam, which are used to
measure the transmitted intensity through the excited and unexcited sample, as
well as to monitor the incoming intensity. Since these three intensity signals
are detected shot-by-shot and simultaneously, this setup allows normalized
shot-by-shot analysis of the transmission. For photon detection, the DSSC
imaging detector, which is capable of recording up to 800 images at 4.5 MHz
frame rate during the FEL burst, is employed and allows approaching the photon
shot-noise limit. We review the setup and its capabilities, as well as the
online and offline analysis tools provided to users.Comment: 11 figure
Stimulated resonant inelastic X-ray scattering in a solid
When materials are exposed to X-ray pulses with sufficiently high intensity, various nonlinear effects can occur. The most fundamental one consists of stimulated electronic decays after resonant absorption of X-rays. Such stimulated decays enhance the number of emitted photons and the emission direction is confined to that of the stimulating incident photons which clone themselves in the process. Here we report the observation of stimulated resonant elastic (REXS) and inelastic (RIXS) X-ray scattering near the cobalt L3 edge in solid Co/Pd multilayer samples. We observe an enhancement of order 106 of the stimulated over the conventional spontaneous RIXS signal into the small acceptance angle of the RIXS spectrometer. We also find that in solids both stimulated REXS and RIXS spectra contain contributions from inelastic electron scattering processes, even for ultrashort 5 fs pulses. Our results reveal the potential and caveats of the development of stimulated RIXS in condensed matter
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