56 research outputs found
Calculation of current-induced torque from spin continuity equation
Current-induced torque is formulated based on the spin continuity equation.
The formulation does not rely on the assumption of separation of local spin and
charge degrees of freedom, in contrast to approaches based on the - model
or mean-field approximation of itinerant ferromagnetism. This new method would
be thus useful for the estimation of torques in actual materials by
first-principles calculations. As an example, the formalism is applied to the
adiabatic limit of the - model in order to obtain the analytical
expression for torques and corresponding terms arising from spin
relaxation due to spin-flip scattering and spin-orbit interaction.Comment: submitted to Phys. Rev.
Anisotropic ferromagnetism in carbon doped zinc oxide from first-principles studies
A density functional theory study of substitutional carbon impurities in ZnO
has been performed, using both the generalized gradient approximation (GGA) and
a hybrid functional (HSE06) as exchange-correlation functional. It is found
that the non-spinpolarized C impurity is under almost all
conditions thermodynamically more stable than the C impurity which
has a magnetic moment of , with the exception of very O-poor
and C-rich conditions. This explains the experimental difficulties in sample
preparation in order to realize -ferromagnetism in C-doped ZnO. From GGA
calculations with large 96-atom supercells, we conclude that two
C-C impurities in ZnO interact ferromagnetically, but
the interaction is found to be short-ranged and anisotropic, much stronger
within the hexagonal -plane of wurtzite ZnO than along the c-axis. This
layered ferromagnetism is attributed to the anisotropy of the dispersion of
carbon impurity bands near the Fermi level for C impurities in
ZnO. From the calculated results, we derive that a C
concentration between 2% and 6% should be optimal to achieve
-ferromagnetism in C-doped ZnO.Comment: 9 pages, 7 figure
First-principles studies on graphene-supported transition metal clusters
Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the binding strength of the TM cluster on to the graphene substrate. Among TM13 clusters, Co-13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe-13 and Ni-13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters
Magnetic properties of small Pt-capped Fe, Co and Ni clusters: A density functional theory study
Theoretical studies on M (M = Fe, Co, Ni) and MPt (for
= 3, 4, 5, 20) clusters including the spin-orbit coupling are done using
density functional theory. The magnetic anisotropy energy (MAE) along with the
spin and orbital moments are calculated for M icosahedral clusters. The
angle-dependent energy differences are modelled using an extended classical
Heisenberg model with local anisotropies. From our studies, the MAE for
Jahn-Teller distorted Fe, Mackay distorted Fe and nearly
undistorted Co clusters are found to be 322, 60 and 5 eV/atom,
respectively, and are large relative to the corresponding bulk values, (which
are 1.4 and 1.3 eV/atom for bcc Fe and fcc Co, respectively.) However, for
Ni (which practically does not show relaxation tendencies), the
calculated value of MAE is found to be 0.64 eV/atom, which is
approximately four times smaller compared to the bulk fcc Ni (2.7
eV/atom). In addition, MAE of the capped cluster (FePt) is
enhanced compared to the uncapped Jahn-Teller distorted Fe cluster
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