We investigate the dynamically polarized nuclear-spin system in Fe/emph{n}-GaAs heterostructures using the response of the electron-spin system to nuclear magnetic resonance (NMR) in lateral spin-valve devices. The hyperfine interaction is known to a
ct more strongly on donor-bound electron states than on those in the conduction band. We provide a quantitative model of the temperature dependence of the occupation of donor sites. With this model we calculate the ratios of the hyperfine and quadrupolar nuclear relaxation rates of each isotope. For all temperatures measured, quadrupolar relaxation limits the spatial extent of nuclear spin-polarization to within a Bohr radius of the donor sites and is directly responsible for the isotope dependence of the measured NMR signal amplitude. The hyperfine interaction is also responsible for the $2text{ kHz}$ Knight shift of the nuclear resonance frequency that is measured as a function of the electron spin accumulation. The Knight shift is shown to provide a measurement of the electron spin-polarization that agrees qualitatively with standard spin transport measurements.
Although pinning of domain walls in ferromagnets is ubiquitous, the absence of an appropriate characterization tool has limited the ability to correlate the physical and magnetic microstructures of ferromagnetic films with specific pinning mechanisms
. Here, we show that the pinning of a magnetic vortex, the simplest possible domain structure in soft ferromagnets, is strongly correlated with surface roughness, and we make a quantitative comparison of the pinning energy and spatial range in films of various thickness. The results demonstrate that thickness fluctuations on the lateral length scale of the vortex core diameter, i.e. an effective roughness at a specific length scale, provides the dominant pinning mechanism. We argue that this mechanism will be important in virtually any soft ferromagnetic film.
We report on an all-electrical measurement of the spin Hall effect in epitaxial Fe/In_{x}Ga_{1-x}As heterostructures with n-type channel doping (Si) and highly doped Schottky tunnel barriers. A transverse spin current generated by an ordinary charge
current flowing in the In_{x}Ga_{1-x}As is detected by measuring the spin accumulation at the edges of the channel. The spin accumulation is identified through the observation of a Hanle effect in the Hall voltage measured by pairs of ferromagnetic contacts. We investigate the bias and temperature dependence of the resulting Hanle signal and determine the skew and side-jump contributions to the total spin Hall conductivity.
Measurements and modeling of electron spin transport and dynamics are used to characterize hyperfine interactions in Fe/GaAs devices with $n$-GaAs channels. Ga and As nuclei are polarized by electrically injected electron spins, and the nuclear polar
ization is detected indirectly through the depolarization of electron spins in the hyperfine field. The dependence of the electron spin signal on injector bias and applied field direction is modeled by a coupled drift-diffusion equation, including effective fields from both the electronic and nuclear polarizations. This approach is used to determine the electron spin polarization independently of the assumptions made in standard transport measurements. The extreme sensitivity of the electron spin dynamics to the nuclear spin polarization also facilitates the electrical detection of nuclear magnetic resonance.
