Spin-dependent electron transport through the ferromagnet/semiconductor interface induced by photon excitation

Circularly polarized light was used to excite electrons with a spin polarization perpendicular to the film plane in 3 nm Au/5 nm Co/GaAs (110) structures. At perpendicular saturation, the bias dependence of the photocurrent was observed to change in the range around 0.7 eV, corresponding to the Schottky barrier height. The photocurrent is observed to change significantly as a function of the magnetization direction with respect to the photon helicity, indicating spin-dependent transport between the semiconductor and the ferromagnetic layer at room temperature

Spin-polarized electron transport processes at the ferromagnet/semiconductor interface

Circularly polarized light was used to excite electrons with a spin polarization perpendicular to the film plane in ferromagnet/semiconductor hybrid structures. The Schottky characteristics at the interface were varied by using NiFe, Co and Fe as the ferromagnet. The Schottky characteristics were clearly observed with NiFe and Co/GaAs, while almost ohmic I-V characteristics were seen with Fe/GaAs. At negative bias a helicity-dependent photocurrent, dependent upon the magnetization configuration of the film and the Schottky barrier height, was detected upon modulating the polarization from right to left circular, For the magnetization along or perpendicular to the surface normal, the helicity-dependent photocurrent In or I 0, respectively, was measured. The asymmetry P=(In-I0)/(In+I0) of the helicity-dependent photocurrent decreases upon increasing the doping density of the GaAs substrates. P also decreases with photon energy h¿ as found for the polarization of photoexcited electrons in GaAs. In NiFe/GaAs samples for h¿=1.59 eV, P=16% for n+=1023 m-3 and P=-23% for p-=1025 m-3 doped substrates, i.e. P is comparable in magnitude to the theoretically predicted spin polarization of 50% for the optically pumped conduction band in GaAs. The results provide unambiguous evidence of spin-polarized electron transport through the ferromagnet/semiconductor interface and show that the Schottky barrier height controls the spin-polarized electron current passing from the semiconductor to the ferromagnet. The asymmetry data indicates that spin-polarized electrons are transmitted from the semiconductor to the ferromagnet with a high efficiency

Magnetic domain studies of permalloy wire-based structures with junctions

Permalloy (Ni-80 Fe-20) wire-based structures (30 nm thick and 1 . w . 10 mum wide) with junctions (crosses, networks, H-shapes, rectangular chains and ring chains) prepared on a GaAs (100) substrate were observed in both their demagnetized and remanent states by magnetic force microscopy (MFM) in order to investigate the role of junction geometry in domain formation, Except in ring chains, two classes of domain configuration are found at the junction: (i) a domain wall-like feature due to abrupt spin rotation and (ii) a triangle-shape domain consistent with a flux closure configuration, Ring chains, on the other hand, form vortex domains at every other junction. The MFM observations are compared with micromagnetic calculations which qualitatively support the magnetic domain configurations

A Discipline-Spanning Overview of Action Research and Its Implications for Technology and Innovation Management

The iterative and learning character of action research is particularly beneficial for exploring complex socio-technical problems in technology and innovation management (TIM). In this respect, action research allows both rigorous and relevant research due to parallel solving of real-world problems, capability building, and gaining scientific insights. However, the use of action research within TIM research is surprisingly limited. Action research also is not a homogeneous research methodology since each research discipline, such as education and organizational science, has its own action research streams, which are often only loosely linked. A systematic overview of those action research traditions and specific best practices is still missing, which complicates a systematic transfer and use of action research in TIM. This article addresses this essential gap by building a cross-disciplinary overview of action research streams based on a bibliometric analysis using Scopus. The analysis includes relevant disciplines with action research traditions, their development over time, and the most influential journals, authors, institutions, and countries. Along with this discipline-spanning analysis, the article investigates particular TIM benefits and challenges of action research. The two key contributions of this article are: 1) a discipline-spanning overview of action research and its evolution and 2) an analysis of its implications for TIM research. These contributions build the basis for strengthening the use of action research in TIM. In the medium-term, action research has the capacity to link academia and industry more closely and, in doing so, assists important endeavours of translating more of our research outcomes into practice

RECAP – A Framework to Support Structured Reflection in Engineering Projects

Reflection is understood as an integral part of designing and design processes. Despite the high relevance and an ongoing discussion about agile engineering, we found that reflection is rarley established in industrial practice. There is a need for an approach structuring the wide range of levels, stakeholders, objects and timing of reflections. The introduced RECAP framework is an important step towards a guideline (heuristic) for reflection in engineering projects. Based on the four dimensions objectives, stakeholders, objects, and processes it supports structured planning of reflection

Magnetization reversal in mesoscopic Ni80Fe20 wires: A magnetic domain launching device

The magnetization reversal process in mesoscopic permalloy (Ni80Fe20) wire structures has been investigated using scanning Kerr microscopy, magnetic force microscopy (MFM) and micromagnetic calculations. We find that the junction offers a site for reversed domain wall nucleation in the narrow part of the wires. As a consequence, the switching field is dominated by the domain nucleation field and the junction region initiates reversal by the wall motion following the nucleation of domains. Our results suggest the possibility of designing structures that can be used to “launch” reverse domains in narrow wires within a controlled field rang

Directional ordering of fluctuations in a two-dimensional compass model

A classical realization of directional coupling in two dimension of the effective orbital-orbital interaction in the Mott insulating phase of the transition metal oxides (TMO) was presented. The model exhibited partial orbital ordering in the form of directional ordering of fluctuation at low temperatures stabilized by an entropy gap. The directional ordering was necessarily accompanied by a lattice distortion and the bond length in horizontal and vertical directions became unequal when the couplings of the orbital isosopin to lattice modes were included. Analysis shows that the compass model has a low temperature phase which exhibited long-ranged correlations in the directions of fluctuations in both isospin and lattice spaces.published_or_final_versio

Mechanical stiffness and anisotropy measured by MRE during brain development in the minipig

The relationship between brain development and mechanical properties of brain tissue is important, but remains incompletely understood, in part due to the challenges in measuring these properties longitudinally over time. In addition, white matter, which is composed of aligned, myelinated, axonal fibers, may be mechanically anisotropic. Here we use data from magnetic resonance elastography (MRE) and diffusion tensor imaging (DTI) to estimate anisotropic mechanical properties in six female Yucatan minipigs at ages from 3 to 6 months. Fiber direction was estimated from the principal axis of the diffusion tensor in each voxel. Harmonic shear waves in the brain were excited by three different configurations of a jaw actuator and measured using a motion-sensitive MR imaging sequence. Anisotropic mechanical properties are estimated from displacement field and fiber direction data with a finite element- based, transversely-isotropic nonlinear inversion (TI-NLI) algorithm. TI-NLI finds spatially resolved TI material properties that minimize the error between measured and simulated displacement fields. Maps of anisotropic mechanical properties in the minipig brain were generated for each animal at all four ages. These maps show that white matter is more dissipative and anisotropic than gray matter, and reveal significant effects of brain development on brain stiffness and structural anisotropy. Changes in brain mechanical properties may be a fundamental biophysical signature of brain development