We discuss fundamental aspects of laser-induced ultrafast demagnetization probed by the time-resolved magneto-optical Kerr effect (MOKE). Studying thin Fe films on MgO substrate in the absence of electronic transport, we demonstrate how to disentangle pump-induced variations of magnetization and magneto-optical coefficients. We provide a mathematical formalism for retrieving genuine laser-induced magnetization dynamics and discuss its applicability in real experimental situations. We further stress the importance of temporal resolution achieved in the experiments and argue that measurements of both time-resolved MOKE rotation and ellipticity are needed for the correct assessment of magnetization dynamics on sub-picosecond timescales. The framework developed here sheds light onto the details of the timeresolved MOKE technique and contributes to the understanding of the interplay between ultrafast laser-induced optical and magnetic effects.
Large area (A = 6 cm 2), thin tantalum films (5 nm < d < 100 nm) are accomplished by evaporation from tantalum rods using small pocket e-beam evaporators. Using a sample to source distance of ≈20 cm, homogeneous amorphous films with a small surface roughness (<1 nm) can be prepared on glass. Films are characterized by scanning electron microscope images, atomic force microscopy, electrochemical oxidation and resistivity measurements as a function of film thickness. The samples show high resistivities of 200-2000 µ cm. The temperature coefficient of the resistivity (TCR) is negative, as characteristic for highly disordered metals. A theoretical description of the thickness distribution (evaporation from plane and hemispherical sources on plane targets) is given in the appendix.
We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy-and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm/fs (close to the Fermi velocity) and the decay length on the order of 100 nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics. arXiv:1810.12237v1 [cond-mat.mes-hall]
Electrochemical cyclovoltammetry experiments were carried out on the platinum surface of a platinum–silicon thin‐film device in sulfuric acid. The internal electronic barrier of the device allows the separation of ground state and excited state charge transfer events released by the electrochemical surface reaction. The traces of the device current show similar features as the cyclovoltammogram and can be discussed in terms of small deviations from the equilibrium state of the thin platinum film. The device current plotted as a function of the electrode potential shows a well‐defined shift of the baseline when hydrogen is adsorbed. This baseline shift may be originated by an adsorbate‐induced change of the chemical potential of the platinum film, thus influencing the internal field in the device (up to values of 23 mV).
Plot of the electrochemical current and the device current as functions of the electrode potential.
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