10 research outputs found
Ni(111)|Graphene|h-BN Junctions as Ideal Spin Injectors
Deposition of graphene on top of hexagonal boron nitride (h-BN) was very
recently demonstrated while graphene is now routinely grown on Ni. Because the
in-plane lattice constants of graphite, h-BN, graphite-like BC2N and of the
close-packed surfaces of Co, Ni and Cu match almost perfectly, it should be
possible to prepare ideal interfaces between these materials which are
respectively, a semimetal, insulator, semiconductor, ferromagnetic and
nonmagnetic metals. Using parameter-free energy minimization and electronic
transport calculations, we show how h-BN can be combined with the perfect spin
filtering property of Ni|graphite and Co|graphite interfaces to make perfect
tunnel junctions or ideal spin injectors (SI) with any desired resistance-area
product.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review
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
A unified first-principles study of Gilbert damping, spin-flip diffusion and resistivity in transition metal alloys
Using a formulation of first-principles scattering theory that includes
disorder and spin-orbit coupling on an equal footing, we calculate the
resistivity , spin flip diffusion length and the Gilbert damping
parameter for NiFe substitutional alloys as a function of
. For the technologically important NiFe alloy, permalloy, we
calculate values of Ohm-cm, nm,
and compared to experimental low-temperature values
in the range Ohm-cm for , nm for , and
for indicating that the theoretical formalism captures
the most important contributions to these parameters.Comment: Published in Physical Review Letter
Spin-orbit-coupling induced domain-wall resistance in diffusive ferromagnets
We investigate diffusive transport through a number of domain wall (DW)
profiles of the important magnetic alloy Permalloy taking into account
simultaneously noncollinearity, alloy disorder, and spin-orbit coupling fully
quantum mechanically, from first principles. In addition to observing the known
effects of magnetization mistracking and anisotropic magnetoresistance, we
discover a not-previously identified contribution to the resistance of a DW
that comes from spin-orbit-coupling-mediated spin-flip scattering in a textured
diffusive ferromagnet. This adiabatic DW resistance, which should exist in all
diffusive DWs, can be observed by varying the DW width in a systematic fashion
in suitably designed nanowires.Comment: 5 pages, 4 figure
First-principles calculations of magnetization relaxation in pure Fe, Co, and Ni with frozen thermal lattice disorder
The effect of the electron-phonon interaction on magnetization relaxation is
studied within the framework of first-principles scattering theory for Fe, Co,
and Ni by displacing atoms in the scattering region randomly with a thermal
distribution. This "frozen thermal lattice disorder" approach reproduces the
non-monotonic damping behaviour observed in ferromagnetic resonance
measurements and yields reasonable quantitative agreement between calculated
and experimental values. It can be readily applied to alloys and easily
extended by determining the atomic displacements from ab initio phonon spectra