The enhancement of Gilbert damping observed for Ni80Fe20 (Py) films in contact with the nonmagnetic metals Cu, Pd, Ta and Pt, is quantitatively reproduced using first-principles scattering calculations. The "spin-pumping" theory that qualitatively explains its dependence on the Py thickness is generalized to include a number of extra factors known to be important for spin transport through interfaces. Determining the parameters in this theory from first-principles shows that interface spin-flipping makes an essential contribution to the damping enhancement. Without it, a much shorter spin-flip diffusion length for Pt would be needed than the value we calculate independently.PACS numbers: 72.25.Mk, 76.50.+g, 75.70.Tj Introduction.-Magnetization dissipation, expressed in terms of the Gilbert damping parameter α, is a key factor determining the performance of magnetic materials in a host of applications. Of particular interest for magnetic memory devices based upon ultrathin magnetic layers [1][2][3] is the enhancement of the damping of ferromagnetic (FM) materials in contact with non-magnetic (NM) metals [4] that can pave the way to tailoring α for particular materials and applications. A "spin pumping" theory has been developed that describes this interface enhancement in terms of a transverse spin current generated by the magnetization dynamics that is pumped into and absorbed by the adjacent NM metal [5,6]. Spin pumping subsequently evolved into a technique to generate pure spin currents that is extensively applied in spintronics experiments [7][8][9].A fundamental limitation of the spin-pumping theory is that it assumes spin conservation at interfaces. This limitation does not apply to a scattering theoretical formulation of the Gilbert damping that is based upon energy conservation, equating the energy lost by the spin system through damping to that parametrically pumped out of the scattering region by the precessing spins [10]. In this Letter, we apply a fully relativistic density functional theory implementation [11][12][13] of this scattering formalism to the Gilbert damping enhancement in those NM|Py|NM structures studied experimentally in Ref. 4. Our calculated values of α as a function of the Py thickness d are compared to the experimental results in Fig. 1. Without introducing any adjustable parameters, we quantitatively reproduce the characteristic 1/d dependence as well as the dependence of the damping on the NM metal.

The spin Hall angle (SHA) is a measure of the efficiency with which a transverse spin current is generated from a charge current by the spin-orbit coupling and disorder in the spin Hall effect (SHE). In a study of the SHE for a Pt|Py (Py=Ni_{80}Fe_{20}) bilayer using a first-principles scattering approach, we find a SHA that increases monotonically with temperature and is proportional to the resistivity for bulk Pt. By decomposing the room temperature SHE and inverse SHE currents into bulk and interface terms, we discover a giant interface SHA that dominates the total inverse SHE current with potentially major consequences for applications.

Local charge and spin currents are evaluated from the solutions of fully relativistic quantum mechanical scattering calculations for systems that include temperature-induced lattice and spin disorder as well as intrinsic alloy disorder. This makes it possible to determine material-specific spin transport parameters at finite temperatures. Illustrations are given for a number of important materials and parameters at 300 K. The spin-flip diffusion length l sf of Pt is determined from the exponential decay of a spin current injected into a long length of thermally disordered Pt; we find l Pt sf = 5.3 ± 0.4 nm. For the ferromagnetic substitutional disordered alloy Permalloy (Py), we inject currents that are fully polarized parallel and antiparallel to the magnetization and calculate l sf from the exponential decay of their difference; we find l Py sf = 2.8 ± 0.1 nm. The transport polarization β is found from the asymptotic polarization of a charge current in a long length of Py to be β = 0.75 ± 0.01. The spin Hall angle ΘsH is determined from the transverse spin current induced by the passage of a longitudinal charge current in thermally disordered Pt; our best estimate is Θ Pt sH = 4.5±1% corresponding to the experimental room temperature bulk resistivity ρ = 10.8µΩ cm.arXiv:1901.00703v1 [cond-mat.mes-hall]

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We show how temperature-induced disorder can be combined in a direct way with first-principles scattering theory to study diffusive transport in real materials. Excellent (good) agreement with experiment is found for the resistivity of Cu, Pd, Pt (and Fe) when lattice (and spin) disorder are calculated from first principles. For Fe, the agreement with experiment is limited by how well the magnetization (of itinerant ferromagnets) can be calculated as a function of temperature. By introducing a simple Debye-like model of spin disorder parameterized to reproduce the experimental magnetization, the temperature dependence of the average resistivity, the anisotropic magnetoresistance and the spin polarization of a Ni80Fe20 alloy are calculated and found to be in good agreement with existing data. Extension of the method to complex, inhomogeneous materials as well as to the calculation of other finite-temperature physical properties within the adiabatic approximation is straightforward.PACS numbers: 72.10. Di, Introduction.-Measuring the temperature dependence of electrical transport is one of the most important and common experimental probes of condensed matter. Although a great deal of what determines the temperature dependence is understood qualitatively [1], there has been virtually no progress in translating this understanding into quantitative, material-specific studies in the past twenty years because of the complexity of the theoretical formalisms [2, 3]; the lowest order variational approximation (LOVA) that is the basis for the successful description of the temperature-dependent electrical and thermal resistivities of a number of elemental metals [3] has to the best of our knowledge not been applied to more complex materials. In particular, it has not been extended to the study of magnetic materials. The need to be able to do so is pressing because current studies of magnetization switching involve large threshold current densities that are accompanied by substantial Joule heating [4].Inspired by the success of the "direct" ab initio molecular dynamics approach to studying structural and electronic properties of matter at finite temperatures introduced by Car and Parrinello [5], we have developed a direct approach to calculate finite-temperature transport properties within the adiabatic approximation. For nonmagnetic (NM) materials, we generate "snapshots" of a thermally disordered solid [6] and use first-principles scattering theory to determine the scattering matrix [7,8] and related properties [9], Fig. 1(a). The results of this two-stage procedure are illustrated by comparing the calculated and experimentally measured temperaturedependent resistivities of the NM metals Cu, Pd and Pt in Fig. 1(b). The purpose of this Letter is to underpin and extend these extremely promising results by including spin-orbit coupling (SOC) [10][11][12][13][14] to determine the temperature dependence of the spin-flip diffusion lengths

The discontinuity of a spin-current through an interface caused by spin-orbit coupling is characterized by the spin memory loss (SML) parameter δ. We use first-principles scattering theory and a recently developed local current scheme to study the SML for Au|Pt, Au|Pd, Py|Pt and Co|Pt interfaces. We find a minimal temperature dependence for nonmagnetic interfaces and a strong dependence for interfaces involving ferromagnets that we attribute to the spin disorder. The SML is larger for Co|Pt than for Py|Pt because the interface is more abrupt. Lattice mismatch and interface alloying strongly enhance the SML that is larger for a Au|Pt than for a Au|Pd interface. The effect of the proximity induced magnetization of Pt is negligible. arXiv:2001.11520v1 [cond-mat.mes-hall] 30 Jan 2020

Symmetry lowering at an interface leads to an enhancement of the effect of spin-orbit coupling and to a discontinuity of spin currents passing through the interface. This discontinuity is characterized by a "spin-memory loss" (SML) parameter δ that has only been determined directly at low temperatures. Although δ is believed to be significant in experiments involving interfaces between ferromagnetic and nonmagnetic metals, especially heavy metals like Pt, it is more often than not neglected to avoid introducing too many unknown interface parameters in addition to often poorly known bulk parameters like the spin-flip diffusion length l sf . In this work, we calculate δ along with the interface resistance AR I and the spin-asymmetry parameter γ as a function of temperature for Co|Pt and Py|Pt interfaces where Py is the ferromagnetic Ni 80 Fe 20 alloy, permalloy. We use first-principles scattering theory to calculate the conductance as well as local charge and spin currents, modeling temperature-induced disorder with frozen thermal lattice and, for ferromagnetic materials, spin disorder within the adiabatic approximation. The bulk and interface parameters are extracted from the spin currents using a Valet-Fert model generalized to include SML.

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