Probing optical spin-currents using THz spin-waves in noncollinear magnetic bilayers

Optically induced spin currents have proven to be useful in spintronics applications, allowing for sub-ps all-optical control of magnetization. However, the mechanism responsible for their generation is still heavily debated. Here we use the excitation of spin-current induced THz spin-waves in noncollinear bilayer structures to directly study optical spin-currents in the time domain. We measure a significant laser-fluence dependence of the spin-wave phase, which can quantitatively be explained assuming the spin current is proportional to the time derivative of the magnetization. Measurements of the absolute spin-wave phase, supported by theoretical calculations and micromagnetic simulations, suggest that a simple ballistic transport picture is sufficient to properly explain spin transport in our experiments and that the damping-like optical STT dominates THz spin-wave generation. Our findings suggest laser-induced demagnetization and spin-current generation share the same microscopic origin.Comment: Supplementary information include

Probing optically induced spin currents using terahertz spin waves in noncollinear magnetic bilayers

Optically-induced spin currents have proven to be useful in spintronics applications, allowing for sub-ps all-optical control of magnetization. However, the mechanism responsible for their generation is still heavily debated. Here we use the excitation of spin-current induced THz spin-waves in noncollinear bilayer structures to study optically-induced spin currents in the time domain. We measure a significant laser-fluence dependence of the spin-wave phase, which can quantitatively be explained assuming the spin current is proportional to the time derivative of the magnetization. Measurements of the absolute spin-wave phase, supported by theoretical calculations and micromagnetic simulations, suggest that angular momentum transfer via the s-d interaction in combination with ballistic interlayer transport is sufficient to fully explain spin-current generation and transport in our experiments. Finally, we show that the damping-like optical STT dominates THz spin-wave generation. Our findings suggest laser-induced demagnetization and spin-current generation share the same microscopic origin

The flow alignment of some nematic liquid crystals

A setup is described to determine the flow alignment angle θ0 in nematic liquid crystals. Results for compounds with and without a strongly polar terminal cyano group indicate that the antiparallel dipole correlation associated with cyano groups has no influence on θ0. The influence of the occurence of a smectic‐A phase on θ0 is investigated on three homologous series. The results show that θ0 is a very sensitive probe for smectic‐like short‐range order. With increasing chain lengths a decrease of θ0 is found, until finally no flow alignment exists anymore. Interestingly, a similar behavior is found in a homologous series without smectic phases

Standard on-column injection : a fast and simple method for large volume injection in medium-resolution gas chromatography

In gas chromatography (GC) large volume injection of samples containing very high molecular weight analytes presents unique problems. Standard programmed-temperature vaporizing or on-column large volume injection systems cannot be used, mainly due to instrumental difficulties. A new, simple solution to this problem is presented. If short, wide-bore columns are used at carrier gas velocities above optimum, the cloud of vapor formed upon evaporation of the solvent can be rapidly discharged from the system by the column flow alone. Hence, in medium-resolution GC, large sample volumes (e.g., 50 L) can be injected using a standard on-column injector. Neither a retention gap nor a solvent vapor exit is needed. The absence of column connectors makes this setup extremely rugged. The optimization of the direct on-column large volume injection is described. The applicability of the new technique for the injection of large volumes of triacylglycerides and heavy mineral oil fractions is shown. It is demonstrated that the new technique is relatively insensitive toward solvent composition. This makes the new method eminently suited for combination with gradient liquid chromatography preseparations