We present a numerical study of dephasing of electron spin ensembles in a diffusive quasi-one-dimensional GaAs wire due to the D'yakonov-Perel' spin-dephasing mechanism. For widths of the wire below the spin precession length and for equal strength of Rashba and linear Dresselhaus spin-orbit fields a strong suppression of spin-dephasing is found. This suppression of spin-dephasing shows a strong dependence on the wire orientation with respect to the crystal lattice. The relevance for realistic cases is evaluated by studying how this effect degrades for deviating strength of Rashba and linear Dresselhaus fields, and with the inclusion of the cubic Dresselhaus term.

We report a study of suppressed spin dephasing for quasi-one-dimensional electron ensembles in wires etched into a GaAs/AlGaAs heterojunction system. Time-resolved Kerr-rotation measurements show a suppression that is most pronounced for wires along the [110] crystal direction. This is the fingerprint of a suppression that is enhanced due to a strong anisotropy in spin-orbit fields that can occur when the Rashba and Dresselhaus contributions are engineered to cancel each other. A surprising observation is that this mechanisms for suppressing spin dephasing is not only effective for electrons in the heterojunction quantum well, but also for electrons in a deeper bulk layer.

Ferromagnetic electrodes of a lateral semiconductor-based spin-valve structure are designed to provide a maximum of spin-polarized injection current. A single-domain state in remanence is a prerequisite obtained by nanostructuring Permalloy thin film electrodes. Three regimes of aspect ratios m are identified by room temperature magnetic force microscopy: (i) high-aspect ratios of m ≥ 20 provide the favored remanent single-domain magnetization states, (ii) medium-aspect ratios m ∼ 3 to m ∼ 20 yield highly remanent states with closure domains and (iii) low-aspect ratios of m ≤ 3 lead to multi-domain structures. Lateral kinks, introduced to bridge the gap between microand macroscale, disturb the uniform magnetization of electrodes with high-and medium-aspect ratios. However, vertical flanks help to maintain a uniformly magnetized state at the ferromagnetsemiconcuctor contact by domain wall pinning.

Magnetotransport measurements were performed on a Permalloy/Mg/SiO 2 /n + -Si (100) spin-valve tunnelling device. Magnetic force microscope imaging proves the single-domain state of the 1 µm elongated and 200 nm wide parallel Permalloy (Py) electrodes. Anisotropic magnetoresistance (AMR) measurements reveal precisely the magnetic field interval of antiparallel magnetization configuration essential for spin-valve operation, in between the switching fields of 15 and 40 mT. Unlike the negative AMR of the Py wires, the tunnelling device shows a small positive magnetoresistance for antiparallel magnetization configuration, as expected for the spin-blockade mechanism.

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