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Register a new userThermoelectric signature of individual skyrmions
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Added by
Alexander Fernandez Scarioni
Publication date
2020
fields
Physics
and research's language is
English
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We experimentally study the thermoelectrical signature of individual skyrmions in chiral Pt/Co/Ru multilayers. Using a combination of controlled nucleation, single skyrmion annihilation, and magnetic field dependent measurements the thermoelectric signature of individual skyrmions is characterized. The observed signature is explained by the anomalous Nernst effect of the skyrmions spin structure. Possible topological contributions to the observed thermoelectrical signature are discussed. Such thermoelectrical characterization allows for non-invasive detection and counting of skyrmions and enables fundamental studies of topological thermoelectric effects on the nano scale
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Magnetic skyrmions are topologically protected whirling spin textures that can be stabilized in magnetic materials in which a chiral interaction is present. Their limited size together with their robustness against the external perturbations promote them as the ultimate magnetic storage bit in a novel generation of memory and logic devices. Despite many examples of the signature of magnetic skyrmions in the electrical signal, only low temperature measurements, mainly in magnetic materials with B20 crystal structure, have demonstrated the skyrmions contribution to the electrical transport properties. Using the combination of Magnetic Force Microscopy (MFM) and Hall resistivity measurements, we demonstrate the electrical detection of sub-100 nm skyrmions in multilayered thin film at room temperature (RT). We furthermore analyse the room temperature Hall signal of a single skyrmion which contribution is mainly dominated by anomalous Hall effect.
Magnetic skyrmions are nanoscale spin structures recently discovered at room temperature (RT) in multilayer films. Employing their novel topological properties towards exciting technological prospects requires a mechanistic understanding of the excitation and relaxation mechanisms governing their stability and dynamics. Here we report on the magnetization dynamics of RT Neel skyrmions in Ir/Fe/Co/Pt multilayer films. We observe a ubiquitous excitation mode in the microwave absorption spectrum, arising from the gyrotropic resonance of topological skyrmions, and robust over a wide range of temperatures and sample compositions. A combination of simulations and analytical calculations establish that the spectrum is shaped by the interplay of interlayer and interfacial magnetic interactions unique to multilayers, yielding skyrmion resonances strongly renormalized to lower frequencies. Our work provides fundamental spectroscopic insights on the spatiotemporal dynamics of topological spin structures, and crucial directions towards their functionalization in nanoscale devices.
The magnetic structure of the in-plane skyrmions in epitaxial MnSi/Si(111) thin films is probed in three dimensions by the combination of polarized neutron reflectometry (PNR) and small angle neutron scattering (SANS). We demonstrate that skyrmions exist in a region of the phase diagram above at temperature of 10 K. PNR shows the skyrmions are confined to the middle of the film due to the potential well formed by the surface twists. However, SANS shows that there is considerable disorder within the plane indicating that the magnetic structure is a 2D skyrmion glass.
We study a quantum dot coupled to two semiconducting reservoirs, when the dot level and the electrochemical potential are both close to a band edge in the reservoirs. This is modelled with an exactly solvable Hamiltonian without interactions (the Fano-Anderson model). The model is known to show an abrupt transition as the dot-reservoir coupling is increased into the strong-coupling regime for a broad class of band structures. This transition involves an infinite-lifetime bound state appearing in the band gap. We find a signature of this transition in the continuum states of the model, visible as a discontinuous behaviour of the dots transmission function. This can result in the steady-state DC electric and thermoelectric responses having a very strong dependence on coupling close to critical coupling. We give examples where the conductances and the thermoelectric power factor exhibit huge peaks at critical coupling, while the thermoelectric figure of merit ZT grows as the coupling approaches critical coupling, with a small dip at critical coupling. The critical coupling is thus a sweet spot for such thermoelectric devices, as the power output is maximal at this point without a significant change of efficiency.
We have simultaneously measured conductance and thermoelectric power (TEP) of individual silicon and germanium/silicon core/shell nanowires in the field effect transistor device configuration. As the applied gate voltage changes, the TEP shows distinctly different behaviors while the electrical conductance exhibits the turn-off, subthreshold, and saturation regimes respectively. At room temperature, peak TEP value of $sim 300 mu$V/K is observed in the subthreshold regime of the Si devices. The temperature dependence of the saturated TEP values are used to estimate the carrier doping of Si nanowires.
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