101 research outputs found
Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface
Although the creation of spin polarization in various non-magnetic media via
electrical spin injection from a ferromagnetic tunnel contact has been
demonstrated, much of the basic behavior is heavily debated. It is reported
here for semiconductor/Al2O3/ferromagnet tunnel structures based on Si or GaAs
that local magnetostatic fields arising from interface roughness dramatically
alter and even dominate the accumulation and dynamics of spins in the
semiconductor. Spin precession in the inhomogeneous magnetic fields is shown to
reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous
and non-collinear with the injector magnetization. The inverted Hanle effect
serves as experimental signature. This interaction needs to be taken into
account in the analysis of experimental data, particularly in extracting the
spin lifetime and its variation with different parameters (temperature, doping
concentration). It produces a broadening of the standard Hanle curve and
thereby an apparent reduction of the spin lifetime. For heavily doped n-type Si
at room temperature it is shown that the spin lifetime is larger than
previously determined, and a new lower bound of 0.29 ns is obtained. The
results are expected to be general and occur for spins near a magnetic
interface not only in semiconductors but also in metals, organic and
carbon-based materials including graphene, and in various spintronic device
structures.Comment: Final version, with text restructured and appendices added (25 pages,
9 figures). To appear in Phys. Rev.
Spin Pumping and Inverse Spin Hall Effect in Platinum: The Essential Role of Spin-Memory Loss at Metallic Interfaces
Through combined ferromagnetic resonance, spin-pumping and inverse spin Hall
effect experiments in Co|Pt bilayers and Co|Cu|Pt trilayers, we demonstrate
consistent values of spin diffusion length
nm and of spin Hall angle for Pt. Our
data and model emphasize on the partial depolarization of the spin current at
each interface due to spin-memory loss. Our model reconciles the previously
published spin Hall angle values and explains the different scaling lengths for
the ferromagnetic damping and the spin Hall effect induced voltage.Comment: 6 pages, 3 figures (main text) and 8 pages supplementary. Published
with small modifications in Phys. Rev. Let
Short-range charge-order in NiO perovskites (=Pr,Nd,Eu) probed by X-ray absorption spectroscopy
The short-range organization around Ni atoms in orthorhombic NiO
(=Pr,Nd,Eu) perovskites has been studied over a wide temperature range by Ni
K-edge x-ray absorption spectroscopy. Our results demonstrate that two
different Ni sites, with different average Ni-O bond lengths, coexist in those
orthorhombic compounds and that important modifications in the Ni nearest
neighbors environment take place across the metal-insulator transition. We
report evidences for the existence of short-range charge-order in the
insulating state, as found in the monoclinic compounds. Moreover, our results
suggest that the two different Ni sites coexists even in the metallic state.
The coexistence of two different Ni sites, independently on the ion,
provides a common ground to describe these compounds and shed new light in the
understanding of the phonon-assisted conduction mechanism and unusual
antiferromagnetism present in all NiO compounds.Comment: 4 pages, 3 figures, accepted PRB - Brief Report Dec.200
Experimental evidences of a large extrinsic spin Hall effect in AuW alloy
We report an experimental study of a gold-tungsten alloy (7% at. W
concentration in Au host) displaying remarkable properties for spintronics
applications using both magneto-transport in lateral spin valve devices and
spin-pumping with inverse spin Hall effect experiments. A very large spin Hall
angle of about 10% is consistently found using both techniques with the
reliable spin diffusion length of 2 nm estimated by the spin sink experiments
in the lateral spin valves. With its chemical stability, high resistivity and
small induced damping, this AuW alloy may find applications in the nearest
future
Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: a tight binding approach
Using an advanced tight-binding approach, we estimate the anisotropy of the
tunnel transmission associated with the rotation of the 5/2 spin of a single Mn
atom forming an acceptor state in GaAs and located near an AlGaAs tunnel
barrier. Significant anisotropies in both in-plane and out-of-plane geometries
are found, resulting from the combination of the large spin-orbit coupling
associated with the p-d exchange interaction, cubic anisotropy of heavy-hole
dispersion and the low C2v symmetry of the chemical bonds.Comment: 4 pages, 3 figure
Electrical spin injection and detection in Germanium using three terminal geometry
In this letter, we report on successful electrical spin injection and
detection in \textit{n}-type germanium-on-insulator (GOI) using a
Co/Py/AlO spin injector and 3-terminal non-local measurements. We
observe an enhanced spin accumulation signal of the order of 1 meV consistent
with the sequential tunneling process via interface states in the vicinity of
the AlO/Ge interface. This spin signal is further observable up to
220 K. Moreover, the presence of a strong \textit{inverted} Hanle effect points
at the influence of random fields arising from interface roughness on the
injected spins.Comment: 4 pages, 3 figure
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