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Register a new userSpin-flip diffusion length in 5d transition metal elements: a first-principles benchmark
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Little is known about the spin-flip diffusion length $l_{rm sf}$, one of the most important material parameters in the field of spintronics. We use a density-functional-theory based scattering approach to determine values of $l_{rm sf}$ that result from electron-phonon scattering as a function of temperature for all 5d transition metal elements. $l_{rm sf}$ does not decrease monotonically with the atomic number Z but is found to be inversely proportional to the density of states at the Fermi level. By using the same local current methodology to calculate the spin Hall angle $Theta_{rm sH}$ that characterizes the efficiency of the spin Hall effect, we show that the products $rho(T)l_{rm sf}(T)$ and $Theta_{rm sH}(T)l_{rm sf}(T)$ are constant.
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Using a formulation of first-principles scattering theory that includes disorder and spin-orbit coupling on an equal footing, we calculate the resistivity $rho$, spin flip diffusion length $l_{sf}$ and the Gilbert damping parameter $alpha$ for Ni$_{1-x}$Fe$_x$ substitutional alloys as a function of $x$. For the technologically important Ni$_{80}$Fe$_{20}$ alloy, permalloy, we calculate values of $rho = 3.5 pm 0.15$ $mu$Ohm-cm, $l_{sf}=5.5 pm 0.3$ nm, and $alpha= 0.0046 pm 0.0001$ compared to experimental low-temperature values in the range $4.2-4.8$ $mu$Ohm-cm for $rho$, $5.0-6.0$ nm for $l_{sf}$, and $0.004-0.013$ for $alpha$ indicating that the theoretical formalism captures the most important contributions to these parameters.
We present a semiclassical theory of spin-diffusion in a ferromagnetic metal subject to a temperature gradient. Spin-flip scattering can generate pure thermal spin currents by short-circuiting spin channels while suppressing spin accumulations. A thermally induced spin density is locally generated when the energy dependence of the density of states is spin polarized.
We employ the spin absorption technique in lateral spin valves to extract the spin diffusion length of Permalloy (Py) as a function of temperature and resistivity. A linear dependence of the spin diffusion length with conductivity of Py is observed, evidencing that Elliott-Yafet is the dominant spin relaxation mechanism in Permalloy. Completing the data set with additional data found in literature, we obtain $lambda_{Py}= (0.91pm 0.04) (fOmega m^2)/rho_{Py}$.
Monolayers of transition metal dichalcogenides (TMDs) have a remarkable excitonic landscape with deeply bound bright and dark exciton states. Their properties are strongly affected by lattice distortions that can be created in a controlled way via strain. Here, we perform a joint theory-experiment study investigating exciton diffusion in strained tungsten disulfide (WS$_2$) monolayers. We reveal a non-trivial and non-monotonic influence of strain. Lattice deformations give rise to different energy shifts for bright and dark excitons changing the excitonic landscape, the efficiency of intervalley scattering channels, and the weight of single exciton species to the overall exciton diffusion. We predict a minimal diffusion coefficient in unstrained WS$_2$ followed by a steep speed-up by a factor of 3 for tensile biaxial strain at about 0.6% strain - in excellent agreement with our experiments. The obtained microscopic insights on the impact of strain on exciton diffusion are applicable to a broad class of multi-valley 2D materials.
The spin Hall effect (SHE) is highly promising for spintronic applications, and the design of materials with large SHE can enable ultra-low power memory technology. Recently, 5d-transition metal oxides have been shown to demonstrate a large SHE. Here we report large values of SHE in four 5d-transition metal anti-perovskites which makes these anti-perovskites promising spintronic materials. We demonstrate that these effects originate in the mixing of dx2-y2 and dxy orbitals caused by spin orbit coupling.
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