129 research outputs found
Thermal Creation of Electron Spin Polarization in n-Type Silicon
Conversion of heat into a spin-current in electron doped silicon can offer a
promising path for spin-caloritronics. Here we create an electron spin
polarization in the conduction band of n-type silicon by producing a
temperature gradient across a ferromagnetic tunnel contact. The substrate
heating experiments induce a large spin signal of 95 V, corresponding to
0.54 meV spin-splitting in the conduction band of n-type silicon by Seebeck
spin tunneling mechanism. The thermal origin of the spin injection has been
confirmed by the quadratic scaling of the spin signal with the Joule heating
current and linear dependence with the heating power
Efficient Spin Injection into Silicon and the Role of the Schottky Barrier
Implementing spin functionalities in Si, and understanding the fundamental
processes of spin injection and detection, are the main challenges in
spintronics. Here we demonstrate large spin polarizations at room temperature,
34% in n-type and 10% in p-type degenerate Si bands, using a narrow Schottky
and a SiO2 tunnel barrier in a direct tunneling regime. Furthermore, by
increasing the width of the Schottky barrier in non-degenerate p-type Si, we
observed a systematic sign reversal of the Hanle signal in the low bias regime.
This dramatic change in the spin injection and detection processes with
increased Schottky barrier resistance may be due to a decoupling of the spins
in the interface states from the bulk band of Si, yielding a transition from a
direct to a localized state assisted tunneling. Our study provides a deeper
insight into the spin transport phenomenon, which should be considered for
electrical spin injection into any semiconductor
Non-linear spin Seebeck effect due to spin-charge interaction in graphene
The abilities to inject and detect spin carriers are fundamental for research
on transport and manipulation of spin information. Pure electronic spin
currents have been recently studied in nanoscale electronic devices using a
non-local lateral geometry, both in metallic systems and in semiconductors. To
unlock the full potential of spintronics we must understand the interactions of
spin with other degrees of freedom, going beyond the prototypical electrical
spin injection and detection using magnetic contacts. Such interactions have
been explored recently, for example, by using spin Hall or spin thermoelectric
effects. Here we present the detection of non-local spin signals using
non-magnetic detectors, via an as yet unexplored non-linear interaction between
spin and charge. In analogy to the Seebeck effect, where a heat current
generates a charge potential, we demonstrate that a spin current in a
paramagnet leads to a charge potential, if the conductivity is energy
dependent. We use graphene as a model system to study this effect, as recently
proposed. The physical concept demonstrated here is generally valid, opening
new possibilities for spintronics
Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes
Spin caloritronics studies the interplay between charge-, heat- and
spin-currents, which are initiated by temperature gradients in magnetic
nanostructures. A plethora of new phenomena has been discovered that promises,
e.g., to make wasted heat in electronic devices useable or to provide new
read-out mechanisms for information. However, only few materials have been
studied so far with Seebeck voltages of only some {\mu}V, which hampers
applications. Here, we demonstrate that half-metallic Heusler compounds are hot
candidates for enhancing spin-dependent thermoelectric effects. This becomes
evident when considering the asymmetry of the spin-split density of electronic
states around the Fermi level that determines the spin-dependent thermoelectric
transport in magnetic tunnel junctions. We identify CoFeAl and CoFeSi
Heusler compounds as ideal due to their energy gaps in the minority density of
states, and demonstrate devices with substantially larger Seebeck voltages and
tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B based
junctions.Comment: 9 pages, 4 figure
Magnon-drag thermopile
arXiv:1203.5628v1Thermoelectric effects in spintronics are gathering increasing attention as a means of managing heat in nanoscale structures and of controlling spin information by using heat flow. Thermal magnons (spin-wave quanta) are expected to play a major role; however, little is known about the underlying physical mechanisms involved. The reason is the lack of information about magnon interactions and of reliable methods to obtain it, in particular for electrical conductors because of the intricate influence of electrons. Here, we demonstrate a conceptually new device that enables us to gather information on magnon–electron scattering and magnon-drag effects. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon-drag thermoelectric effects. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. This information is crucial to understand the physics of electron–magnon interactions, magnon dynamics and thermal spin transport.This research was supported by the Spanish Ministerio de Ciencia e Innovación, MICINN (MAT2010-18065) and by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement NANOFUNCTION no 257375.Peer Reviewe
Spin-dependent phenomena and device concepts explored in (Ga,Mn)As
Over the past two decades, the research of (Ga,Mn)As has led to a deeper
understanding of relativistic spin-dependent phenomena in magnetic systems. It
has also led to discoveries of new effects and demonstrations of unprecedented
functionalities of experimental spintronic devices with general applicability
to a wide range of materials. In this article we review the basic material
properties that make (Ga,Mn)As a favorable test-bed system for spintronics
research and discuss contributions of (Ga,Mn)As studies in the general context
of the spin-dependent phenomena and device concepts. Special focus is on the
spin-orbit coupling induced effects and the reviewed topics include the
interaction of spin with electrical current, light, and heat.Comment: 47 pages, 41 figure
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