1,940 research outputs found
Intersublattice magnetocrystalline anisotropy using a realistic tight-binding method based on maximally localized Wannier functions
Using a realistic tight-binding Hamiltonian based on maximally localized
Wannier functions, we investigate the two-ion magnetocrystalline anisotropy
energy (MAE) in transition metal compounds. MAE contributions from
throughout the Brillouin zone are obtained using magnetic force theorem
calculations with and without perturbation theory. The results from either
method agree with one another, and both reflect features of the Fermi surface.
The intra-sublattice and inter-sublattice contributions to MAE are evaluated
using a Green's function method. We find that the sign of the inter-sublattice
contribution varies among compounds, and that its amplitude may be significant,
suggesting MAE can not be resolved accurately in a single-ion manner. The
results are further validated by scaling spin-orbit-coupling strength in
density functional theory. Overall, this realistic tight-binding method provide
an effective approach to evaluate and analyze MAE while retaining the accuracy
of corresponding first-principles methods.Comment: 11 pages, 7 figure
Band-filling effect on magnetic anisotropy using a Green's function method
We use an analytical model to describe the magnetocrystalline anisotropy
energy (MAE) in solids as a function of band filling. The MAE is evaluated in
second-order perturbation theory, which makes it possible to decompose the MAE
into a sum of transitions between occupied and unoccupied pairs. The model
enables us to characterize the MAE as a sum of contributions from different,
often competing terms. The nitridometalates Li[(LiT)N],
with =Mn, Fe, Co, Ni, provide a system where the model is very effective
because atomic like orbital characters are preserved and the decomposition is
fairly clean. Model results are also compared against MAE evaluated directly
from first-principles calculations for this system. Good qualitative agreement
is found
Spin excitations in KFeSe: linear response approach
Using \emph{ab initio} linear response techniques we calculate spin wave
spectra in KFeSe, and find it to be in excellent agreement
with a recent experiment. The spectrum can be alternatively described rather
well by localized spin Hamiltonian restricted to first and second nearest
neighbor couplings. We confirm that exchange coupling between nearest neighbor
Fe magnetic moments is strongly anisotropic, and show directly that in the
ideal system this anisotropy has itinerant nature which can be imitated by
introducing higher order terms in effective localized spin Hamiltonian
(biquadratic coupling). In the real system, structural relaxation provides an
additional source of the exchange anisotropy of approximately the same
magnitude. The dependence of spin wave spectra on filling of Fe vacancy sites
is also discussed
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