1,078 research outputs found
Interface enhancement of Gilbert damping from first-principles
The enhancement of Gilbert damping observed for Ni80Fe20 (Py) films in
contact with the non-magnetic metals Cu, Pd, Ta and Pt, is quantitatively
reproduced using first-principles scattering theory. The "spin-pumping" theory
that qualitatively explains its dependence on the Py thickness is generalized
to include a number of 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
Gilbert damping in noncollinear ferromagnets
The precession and damping of a collinear magnetization displaced from its
equilibrium are described by the Landau-Lifshitz-Gilbert equation. For a
noncollinear magnetization, it is not known how the damping should be
described. We use first-principles scattering theory to investigate the damping
in one-dimensional transverse domain walls (DWs) of the important ferromagnetic
alloy NiFe and interpret the results in terms of phenomenological
models. The damping is found to depend not only on the magnetization texture
but also on the specific dynamic modes of Bloch and N\'eel DWs. Even in the
highly disordered NiFe alloy, the damping is found to be
remarkably nonlocal.Comment: Final version accepted by Physical Review Letter
Direct Method for Calculating Temperature-Dependent Transport Properties
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 NiFe
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.Comment: Accepted as a Rapid Communication in Physical Review
Calculating the transport properties of magnetic materials from first-principles including thermal and alloy disorder, non-collinearity and spin-orbit coupling
A density functional theory based two-terminal scattering formalism that
includes spin-orbit coupling and spin non-collinearity is described. An
implementation using tight-binding muffin-tin orbitals combined with extensive
use of sparse matrix techniques allows a wide variety of inhomogeneous
structures to be flexibly modelled with various types of disorder including
temperature induced lattice and spin disorder. The methodology is illustrated
with calculations of the temperature dependent resistivity and magnetization
damping for the important substitutional disordered magnetic alloy Permalloy
(Py), NiFe. Comparison of calculated results with recent
experimental measurements of the damping (including its temperature dependence)
indicates that the scattering approach captures the most important
contributions to this important property.Comment: 26 pages, 24 figure
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