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Register a new userAttenuation characteristics of spin pumping signal due to travelling spin waves
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The authors have investigated the contribution of the surface spin waves to spin pumping. A Pt/NiFe bilayer has been used for measuring spin waves and spin pumping signals simultaneously. The theoretical framework of spin pumping resulting from ferromagnetic resonance has been extended to incorporate spin pumping due to spin waves. Equations for the effective area of spin pumping due to spin waves have been derived. The amplitude of the spin pumping signal resulting from travelling waves is shown to decrease more rapidly with precession frequency than that resulting from standing waves and show good agreement with the experimental data.
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Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect, i.e. measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1-x)2Te3 to a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable spin Seebeck effect which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual spin Seebeck effect in metals and therefore opens up exciting possibilities in spintronics.
We theoretically investigate a manipulation method of nonequilibrium spin accumulation in the paramagnetic normal metal of a spin pumping system, by using the spin precession motion combined with the spin diffusion transport. We demonstrate based on the Bloch-Torrey equation that the direction of the nonequilibrium spin accumulation is changed by applying an additional external magnetic field, and consequently, the inverse spin Hall voltage in an adjacent paramagnetic heavy metal changes its sign. We find that the spin relaxation time and the spin diffusion length are simultaneously determined by changing the magnitude of the external magnetic field and the thickness of the normal metal in a commonly-used spin pumping system.
Spin pumping by ferromagnetic resonance is one of the most common technique to determine spin hall angles, Edelstein lengths or spin diffusion lengths of a large variety of materials. In recent years, rising concerns have appeared regarding the interpretation of these experiments, underlining that the signal could arise purely from thermoelectric effects, rather than from coherent spin pumping. Here, we propose a method to evaluate the presence or absence of thermal effects in spin pumping signals, by combining bolometry and spin pumping by ferromagnetic resonance measurements, and comparing their timescale. Using a cavity to perform the experiments on PtPermalloy and La0.7Sr0.3MnO3Pt samples, we conclude on the absence of any measurable thermoelectric contribution such as the spin Seebeck and anomalous Nernst effects at resonance
We have measured the inverse spin Hall effect (ISHE) in textit{n}-Ge at room temperature. The spin current in germanium was generated by spin pumping from a CoFeB/MgO magnetic tunnel junction in order to prevent the impedance mismatch issue. A clear electromotive force was measured in Ge at the ferromagnetic resonance of CoFeB. The same study was then carried out on several test samples, in particular we have investigated the influence of the MgO tunnel barrier and sample annealing on the ISHE signal. First, the reference CoFeB/MgO bilayer grown on SiO$_{2}$ exhibits a clear electromotive force due to anisotropic magnetoresistance and anomalous Hall effect which is dominated by an asymmetric contribution with respect to the resonance field. We also found that the MgO tunnel barrier is essential to observe ISHE in Ge and that sample annealing systematically lead to an increase of the signal. We propose a theoretical model based on the presence of localized states at the interface between the MgO tunnel barrier and Ge to account for these observations. Finally, all of our results are fully consistent with the observation of ISHE in heavily doped $n$-Ge and we could estimate the spin Hall angle at room temperature to be $approx$0.001.
We show that the resonant coupling of phonons and magnons can be exploited to generate spin currents at room temperature. Surface acoustic wave (SAW) pulses with a frequency of 1.55 GHz and duration of 300 ns provide coherent elastic waves in a ferromagnetic thin film/normal metal (Co/Pt) bilayer. We use the inverse spin Hall voltage in the Pt as a measure for the spin current and record its evolution as a function of time and external magnetic field magnitude and orientation. Our experiments show that a spin current is generated in the exclusive presence of a resonant elastic excitation. This establishes acoustic spin pumping as a resonant analogue to the spin Seebeck effect.
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