82 research outputs found
Effect of iron thicknesses on spin transport in a Fe/Au bilayer system
This paper is concerned with a theoretical analysis of the behavior of
optically excited spin currents in bilayer and multilayer systems of
ferromagnetic and normal metals. As the propagation, control and manipulation
of the spin currents created in ferromagnets by femtosecond optical pulses is
of particular interest, we examine the influence of different thicknesses of
the constituent layers for the case of electrons excited several electronvolts
above the Fermi level. Using a Monte-Carlo simulation framework for such highly
excited electrons, we first examine the spatio-temporal characteristics of the
spin current density driven in a Fe layer, where the absorption profile of the
light pulses plays an important role. Further, we examine how the combination
of light absorption profiles, spin-dependent transmission probabilities, and
iron layer thicknesses affect spin current density in a Fe/Au bilayer system.
For high-energy electrons studied here, the interface and secondary electron
generation have a small influence on spin transport in the bilayer system.
However, we find that spin injection from one layer to another is most
effective within a certain range of iron layer thicknesses
Ultrafast optically induced spin transfer in ferromagnetic alloys
The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism
Laser Induced Creation of Antiferromagnetic 180 Degree Domains in NiO Pt Bilayers
The antiferromagnetic order in heterostructures of NiO Pt thin films can be modified by optical pulses. After the irradiation with laser light, the optically induced creation of antiferromagnetic domains can be observed by imaging the created domain structure utilizing the X ray magnetic linear dichroism effect. The effect of different laser polarizations on the domain formation can be studied and used to identify a polarization independent creation of 180 domain walls and domains with 180 different N el vector orientation. By varying the irradiation parameters, the switching mechanism can be determined to be thermally induced. This study demonstrates experimentally the possibility to optically create antiferromagnetic domains, an important step towards future functionalization of all optical switching mechanisms in antiferromagnet
The 2021 ultrafast spectroscopic probes of condensed matter roadmap
In the 60 years since the invention of the laser, the scientific community has developed numerous fields of research based on these bright, coherent light sources, including the areas of imaging, spectroscopy, materials processing and communications. Ultrafast spectroscopy and imaging techniques are at the forefront of research into the light–matter interaction at the shortest times accessible to experiments, ranging from a few attoseconds to nanoseconds. Light pulses provide a crucial probe of the dynamical motion of charges, spins, and atoms on picosecond, femtosecond, and down to attosecond timescales, none of which are accessible even with the fastest electronic devices. Furthermore, strong light pulses can drive materials into unusual phases, with exotic properties. In this roadmap we describe the current state-of-the-art in experimental and theoretical studies of condensed matter using ultrafast probes. In each contribution, the authors also use their extensive knowledge to highlight challenges and predict future trends
Refined Baum-Katz laws for weighted sums of iid random variables
We consider weighted sums with iid random variables (Xn) and compare the tail probabilities of these sums with the moment conditions on X1. If X1 is in the domain of attraction of a stable law then refined Baum-Katz laws generalizing results of Heyde, Gut and other authors are presented. Some special examples of weights pnk originating from summability are discussed.Tail probabilities Baum-Katz laws Weighted means of iid random variables
Maxima of increments of partial sums for certain subexponential distributions
We consider partial sums of i.i.d. random variables with moments E(X1)=0, E(X12)=[sigma]2 and and show thatwith some explicit function [phi](·). A related result for random variables with exponentially thin tails has recently been shown by Steinebach, extending a result given by Shao.Partial sums Independent random variables Maxima of increments Limit theorem Subexponential distributions a.s. convergence
Effects of passing wakes on a separating boundary layer along a low-pressure turbine blade through large-eddy simulation
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