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Register a new userTemperature dependence of spin diffusion length and spin Hall angle in Au and Pt
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We have studied the spin transport and the spin Hall effect as a function of temperature for platinum (Pt) and gold (Au) in lateral spin valve structures. First, by using the spin absorption technique, we extract the spin diffusion length of Pt and Au. Secondly, using the same devices, we have measured the spin Hall conductivity and analyzed its evolution with temperature to identify the dominant scattering mechanisms behind the spin Hall effect. This analysis confirms that the intrinsic mechanism dominates in Pt whereas extrinsic effects are more relevant in Au. Moreover, we identify and quantify the phonon-induced skew scattering. We show that this contribution to skew scattering becomes relevant in metals such as Au, with a low residual resistivity.
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Antiferromagnetic Weyl semimetal Mn$_3$Sn has shown to generate strong intrinsic anomalous Hall effect (AHE) at room temperature, due to large momentum-space Berry curvature from the time-reversal symmetry breaking electronic bands of the Kagome planes. This prompts us to investigate intrinsic spin Hall effect, a transverse phenomenon with identical origin as the intrinsic AHE. We report inverse spin Hall effect experiments in nanocrystalline Mn$_3$Sn nanowires at room temperature using spin absorption method which enables us to quantitatively derive both the spin diffusion length and the spin Hall angle in the same device. We observed clear absorption of the spin current in the Mn$_3$Sn nanowires when kept in contact with the spin transport channel of a lateral spin-valve device. We estimate spin diffusion length $lambda_{s(Mn_3Sn)}$ $sim$0.75 $pm$0.67 nm from the comparison of spin signal of an identical reference lateral spin valve without Mn$_3$Sn nanowire. From inverse spin Hall measurements, we evaluate spin Hall angle $theta_{SH}$ $sim$5.3 $pm$ 2.4 $%$ and spin Hall conductivity $sigma_{SH}$ $sim$46.9 $pm$ 3.4 ($hbar/e$) ($Omega$ cm)$^{-1}$. The estimated spin Hall conductivity agrees with both in sign and magnitude to the theoretically predicted intrinsic $sigma_{SH}^{int}$ $sim$36-96 ($hbar/e$) ($Omega$ cm)$^{-1}$. We also observed anomalous Hall effect at room temperature in nano-Hall bars prepared at the same time as the spin Hall devices. Large anomalous Hall conductivity along with adequate spin Hall conductivity makes Mn$_3$Sn a promising material for ultrafast and ultrahigh-density spintronics devices.
Understanding the evolution of spin-orbit torque (SOT) with increasing heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical for the development of magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and damping-like SOT regarding their dependence on NM thickness. Here, using linewidth and phase-resolved amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract damping enhancement and both field-like and damping-like inverse SOT in Ni$_{80}$Fe$_{20}$/Pt bilayers as a function of Pt thickness. By enforcing an interpretation of the data which satisfies Onsager reciprocity, we find that both the damping enhancement and damping-like inverse SOT can be described by a single spin diffusion length ($approx$ 4 nm), and that we can separate the spin pumping and spin memory loss (SML) contributions to the total damping. This analysis indicates that less than 40% of the angular momentum pumped by FMR through the Ni$_{80}$Fe$_{20}$/Pt interface is transported as spin current into the Pt. On account of the SML and corresponding reduction in total spin current available for spin-charge transduction in the Pt, we determine the Pt spin Hall conductivity ($sigma_mathrm{SH} = (2.36 pm 0.04)times10^6 Omega^{-1} mathrm{m}^{-1}$) and bulk spin Hall angle ($theta_mathrm{SH}=0.387 pm0.008$) to be larger than commonly-cited values. These results suggest that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize SML. Lastly, we find that self-consistent fitting of the damping and SOT data is best achieved by a model with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such that both the spin diffusion length and spin Hall conductivity are proportional to the Pt charge conductivity.
We present a systematic study of the temperature dependence of diffusive magnon spin transport, using a non-local device geometry. In our measurements, we detect spin signals arising from electrical and thermal magnon generation, and we directly extract the magnon spin diffusion length $lambda_m$ for temperatures from 2 to 293 K. Values of $lambda_m$ obtained from electrical and thermal generation agree within the experimental error, with $lambda_m=9.6pm0.9$ $mu$m at room temperature to a minimum of $lambda_m=5.5pm0.7$ $mu$m at 30 K. Using a 2D finite element model to fit the data obtained for electrical magnon generation we extract the magnon spin conductivity $sigma_m$ as a function of temperature, which is reduced from $sigma_m=5.1pm0.2times10^5$ S/m at room temperature to $sigma_m=0.7pm0.4times10^5$ S/m at 5 K. Finally, we observe an enhancement of the signal originating from thermally generated magnons for low temperatures, where a maximum is observed around $T=7$ K. An explanation for this low temperature enhancement is however still missing and requires additional investigations.
In this study, the temperature dependence of the spin Hall angle of palladium (Pd) was experimentally investigated by spin pumping. A Ni80Fe20/Pd bilayer thin film was prepared, and a pure spin current was dynamically injected into the Pd layer. This caused the conversion of the spin current to a charge current owing to the inverse spin Hall effect. It was found that the spin Hall angle varies as a function of temperature, whereby the value of the spin Hall angle increases to ca. 0.02 at 123 K.
We investigated spin Hall magnetoresistance in FeMn/Pt bilayers, which was found to be one order of magnitude larger than that of heavy metal and insulating ferromagnet or antiferromagnet bilayer systems, and comparable to that of NiFe/Pt bilayers. The spin Hall magnetoresistance shows a non-monotonic dependence on the thicknesses of both FeMn and Pt. The former can be accounted for by the thickness dependence of net magnetization in FeMn thin films, whereas the latter is mainly due to spin accumulation and diffusion in Pt. Through analysis of the Pt thickness dependence, the spin Hall angle, spin diffusion length of Pt and the real part of spin mixing conductance were determined to be 0.2, 1.1 nm, and $5.5 * 10^{14} {Omega}^{-1} m^{-2}$, respectively. The results corroborate the spin orbit torque effect observed in this system recently.
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