51 research outputs found
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
Electrical and thermal spin accumulation in germanium
In this letter, we first show electrical spin injection in the germanium
conduction band at room temperature and modulate the spin signal by applying a
gate voltage to the channel. The corresponding signal modulation agrees well
with the predictions of spin diffusion models. Then by setting a temperature
gradient between germanium and the ferromagnet, we create a thermal spin
accumulation in germanium without any tunnel charge current. We show that
temperature gradients yield larger spin accumulations than pure electrical spin
injection but, due to competing microscopic effects, the thermal spin
accumulation in germanium remains surprisingly almost unchanged under the
application of a gate voltage to the channel.Comment: 7 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
Crossover from spin accumulation into interface states to spin injection in the germanium conduction band
Electrical spin injection into semiconductors paves the way for exploring new
phenomena in the area of spin physics and new generations of spintronic
devices. However the exact role of interface states in spin injection mechanism
from a magnetic tunnel junction into a semiconductor is still under debate. In
this letter, we demonstrate a clear transition from spin accumulation into
interface states to spin injection in the conduction band of -Ge. We observe
spin signal amplification at low temperature due to spin accumulation into
interface states followed by a clear transition towards spin injection in the
conduction band from 200 K up to room temperature. In this regime, the spin
signal is reduced down to a value compatible with spin diffusion model. More
interestingly, we demonstrate in this regime a significant modulation of the
spin signal by spin pumping generated by ferromagnetic resonance and also by
applying a back-gate voltage which are clear manifestations of spin current and
accumulation in the germanium conduction band.Comment: 5 pages, 4 figure
Unconventional anomalous Hall effect in 3d/5d multilayers mediated by the nonlocal spin-conductivity
We evidenced unconventionnal Anomalous Hall Effects (AHE) in 3d/5d
(Co0.2nm/Ni0.6nm)N multilayers grown on a thin Pt layer or thin Au:W alloy. The
inversion observed on AHE originates from the opposite sign of the spin-orbit
coupling of Pt compared to Ni. Via advanced simulations methods for the
description of the spin-current profiles based on the spin-dependent Boltzmann
formalism, we extracted the spin Hall angle (SHA) of Pt and (Co/Ni) as well as
the relevant transport parameters. The extracted SHA for Pt, +20%, is opposite
to the one of (Co/Ni), giving rise to an effective AHE inversion for thin
(Co/Ni) multilayers (N < 17). The spin Hall angle in Pt is found to be larger
than the one previously measured in combined spin-pumping inverse spin-Hall
effect experiments in a geometry of current perpendicular to plane. Whereas
magnetic proximity effects cannot explain the effect, spin-current leakage and
anisotropic electron scattering at Pt/(Co,Ni) interfaces fit the experiments.Comment: 7 pages, 2 figure
Quantifying orbital Rashba effect via harmonic Hall torque measurements in transition-metal|Cu|Oxide structures
Spin-orbit interaction (SOI) plays a pivotal role in the charge-to-spin
conversion mechanisms, notably the spin Hall effect involving spin-dependent
deflection of conduction electrons and the interfacial spin Rashba-Edelstein
effect. In recent developments, significant current-induced torques have been
predicted and observed in material systems featuring interfaces with light
elements \textit{i.e.} possessing a weak SOI. These findings challenge existing
mechanisms and point to the potential involvement of the orbital counterpart of
electrons, namely the orbital Hall and orbital Rashba effects. Here, we
establish, in Pt|Co|Cu|AlOx stacking, the comparable strength between the
orbital Rashba effect at the Cu|AlOx interface and the effective spin Hall
effect in Pt|Co. Subsequently, we investigate the thickness dependence of an
intermediate Pt layer in Co|Pt|Cu|CuOx, revealing the strong signature of the
orbital Rashba effect at the Cu|CuOx interface besides the well-identified Pt
intrinsic spin Hall effect. Leveraging such contribution from the orbital
Rashba effect, we show a twofold enhancement in the effective torques on Co
through harmonic Hall measurements. This result is corroborated by
complementary spin Hall magneto-resistance and THz spectroscopy experiments.
Our results unveil unexplored aspects of the electron's orbital degree of
freedom, offering an alternative avenue for magnetization manipulation in
spintronic devices with potential implications for energy-efficient and
environmentally friendly technologies using abundant and light elements.Comment: 11 pages, 5 figure
Field dependence of magnetization reversal by spin transfer
We analyse the effect of the applied field (Happl) on the current-driven
magnetization reversal in pillar-shaped Co/Cu/Co trilayers, where we observe
two different types of transition between the parallel (P) and antiparallel
(AP) magnetic configurations of the Co layers. If Happl is weaker than a rather
small threshold value, the transitions between P and AP are irreversible and
relatively sharp. For Happl exceding the threshold value, the same transitions
are progressive and reversible. We show that the criteria for the stability of
the P and AP states and the experimentally observed behavior can be precisely
accounted for by introducing the current-induced torque of the spin transfer
models in a Landau-Lifschitz-Gilbert equation. This approach also provides a
good description for the field dependence of the critical currents
Ultrafast spin-currents and charge conversion at \u3ci\u3e3d-5d\u3c/i\u3e interfaces probed by time-domain terahertz spectroscopy
Spintronic structures are extensively investigated for their spin-orbit torque properties, required for magnetic commutation functionalities. Current progress in these materials is dependent on the interface engineering for the optimization of spin transmission. Here, we advance the analysis of ultrafast spin-charge conversion phenomena at ferromagnetic-Transition metal interfaces due to their inverse spin-Hall effect properties. In particular, the intrinsic inverse spin-Hall effect of Pt-based systems and extrinsic inverse spin-Hall effect of Au:W and Au:Ta in NiFe/Au:(W,Ta) bilayers are investigated. The spin-charge conversion is probed by complementary techniques-ultrafast THz time-domain spectroscopy in the dynamic regime for THz pulse emission and ferromagnetic resonance spin-pumping measurements in the GHz regime in the steady state-to determine the role played by the material properties, resistivities, spin transmission at metallic interfaces, and spin-flip rates. These measurements show the correspondence between the THz time-domain spectroscopy and ferromagnetic spin-pumping for the different set of samples in term of the spin mixing conductance. The latter quantity is a critical parameter, determining the strength of the THz emission from spintronic interfaces. This is further supported by ab initio calculations, simulations, and analysis of the spin-diffusion and spin-relaxation of carriers within the multilayers in the time domain, permitting one to determine the main trends and the role of spin transmission at interfaces. This work illustrates that time-domain spectroscopy for spin-based THz emission is a powerful technique to probe spin-dynamics at active spintronic interfaces and to extract key material properties for spin-charge conversion
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