P. Nemec

Spin Hall effect transistor.

In a Spin Hall The spin Hall effect, in which an electrical current causes accumulation of electron spins of opposite signs in the direction transverse to the current flow, provides a promising avenue of research in exploiting the spin degree of freedom in electronic devices. However, implementing the effect in a device is challenging. Wunderlich et al. (p. 1801) combine the concept of the spin Hall effect with that of a spin transistor, and build a nonmagnetic device in a which a spin current, injected by optical means, is “stripped” of its charge component, goes through a spin-modulation layer, and is detected using the inverse spin Hall effect. Such manipulation of the spin current may help in future spintronic applications. Manipulation of the spin degree of freedom of electrons is used to build a spin transistor without magnetic materials. The field of semiconductor spintronics explores spin-related quantum relativistic phenomena in solid-state systems. Spin transistors and spin Hall effects have been two separate leading directions of research in this field. We have combined the two directions by realizing an all-semiconductor spin Hall effect transistor. The device uses diffusive transport and operates without electrical current in the active part of the transistor. We demonstrate a spin AND logic function in a semiconductor channel with two gates. Our study shows the utility of the spin Hall effect in a microelectronic device geometry, realizes the spin transistor with electrical detection directly along the gated semiconductor channel, and provides an experimental tool for exploring spin Hall and spin precession phenomena in an electrically tunable semiconductor layer.

Antiferromagnetic structure in tetragonal CuMnAs thin films

Tetragonal CuMnAs is an antiferromagnetic material with favourable properties for applications in spintronics. Using a combination of neutron diffraction and x-ray magnetic linear dichroism, we determine the spin axis and magnetic structure in tetragonal CuMnAs, and reveal the presence of an interfacial uniaxial magnetic anisotropy. From the temperature-dependence of the neutron diffraction intensities, the Néel temperature is shown to be (480 ± 5) K. Ab initio calculations indicate a weak anisotropy in the (ab) plane for bulk crystals, with a large anisotropy energy barrier between in-plane and perpendicular-to-plane directions.

Laser-Induced Precession of Magnetization in GaMnAs

We report on the photo-induced precession of the ferromagnetically coupled Mn spins in (Ga,Mn)As, which is observed even with no external magnetic field applied. We concentrate on various experimental aspects of the time-resolved magneto-optical Kerr effect (TR-MOKE) technique that can be used to clarify the origin of the detected signals. We show that the measured data typically consist of several different contributions, among which only the oscillatory signal is directly connected with the ferromagnetic order in the sample.

Negative and positive nonlinear absorption in CdS-doped glasses

. Weinvestigated photodarkend samples, which were exposed to pump light for a long time(about 1 h). Fig.1The optical transmission spectra of the samples studied are shown in Fig. 1. All thesamples are doped by CdS, and different positions of the absorption edge are due tothe different nanocrystal sizes (effect of quantum confinement). We observed negative2

Piezoelectric and photon helicity dependent domain wall motion driven by electrical current and optical spin transfer torques

Summary form only given. The rich internal degrees of freedom of magnetic domain walls (DW) make them an attractive complement to electron charge for exploring new concepts of storage, transport, and processing of information. We utilize the tuneable internal structure of a DW in perpendicularly magnetized GaMnAsP/GaAs ferromagnetic semiconductor and demonstrate devices in which piezo-electrically controlled magnetic anisotropy yields large mobility variations for current driven DW motion . [1, 2] We directly observe and piezo-electric control the Walker breakdown separating two regimes with different mobilities . The piezo-electric control allows to experimentally assess the upper and lower boundaries of the characteristic ratio of adiabatic and non-adiabatic spin transfer torques in the current driven DW motion . Apart from current induced DW motion, also optically generated electron spins can move DWs . The direction of DW motion depends on the photon helicity in our GaMnAsP/GaAs devices and we identify optical spin transfer torque (oSTT) [4] as the underlying mechanism . We further discuss possibilities to apply and electrically control oSTT induced DW motion to thin magnetic metal films . Optically driven DW motion can be very efficient and high velocities maybe achieved since intrinsic DW pinning [5] does not occur when the entire DW is simultaneously exposed to perpendicular polarized electron spins . We also identify a polarisation independent contribution for light-induced DW motion where the DW is attracted to the hot-spot generated by the focused laser light . Unlike magnetic field and current driven DW motion, light-induced DW motion provides an optical tweezers like ability to position and locally probe DWs .