167 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
Electron correlation effects on exchange interactions and spin excitations in 2D van der Waals materials
Despite serious effort, the nature of the magnetic interactions and the role
of electron-correlation effects in magnetic two-dimensional (2D) van der Waals
materials remain elusive. Using CrI as a model system, we show that the
calculated electronic structure including nonlocal electron correlations yields
spin excitations consistent with inelastic neutron scattering measurements.
Remarkably, this approach identifies an unreported correlation-enhanced
interlayer super-superexchange, which rotates the magnon Dirac lines off, and
introduces a gap along, the high-symmetry -- path. This discovery
provides a different perspective on the gap opening mechanism observed in
CrI, which was previously associated with spin-orbit coupling through the
Dzyaloshinskii-Moriya interaction or Kitaev interaction. Our observation
elucidates the critical role of electron correlations on the spin ordering and
spin dynamics in magnetic van der Waals materials and demonstrates the
necessity of explicit treatment of electron correlations in the broad family of
2D magnetic materials.Comment: 16 pages, 8 figure
Intrinsic magnetic properties in R(Fe1−xCox)11TiZ(R=Yand Ce;Z=H,C,and N)
To guide improved properties coincident with reduction of critical materials in permanent magnets, we investigate via density functional theory (DFT) the intrinsic magnetic properties of a promising system, R(Fe1−xCox)11TiZ with R=Y, Ce and interstitial doping (Z=H,C,N). The magnetization M, Curie temperature TC, and magnetocrystalline anisotropy energy K calculated in local density approximation to DFT agree well with measurements. Site-resolved contributions to K reveal that all three Fe sublattices promote uniaxial anisotropy in YFe11Ti, while competing anisotropy contributions exist in YCo11Ti. As observed in experiments on R(Fe1−xCox)11Ti, we find a complex nonmonotonic dependence of K on Co content and show that anisotropy variations are a collective effect of MAE contributions from all sites and cannot be solely explained by preferential site occupancy. With interstitial doping, calculated TC enhancements are in the sequence of N\u3eC\u3eH, with volume and chemical effects contributing to the enhancement. The uniaxial anisotropy of R(Fe1−xCox)11TiZ generally decreases with C and N; although, for R=Ce, C doping is found to greatly enhance it for a small range of 0.
Intrinsic magnetic properties in R(Fe1−xCox)11TiZ(R=Yand Ce;Z=H,C,and N)
To guide improved properties coincident with reduction of critical materials in permanent magnets, we investigate via density functional theory (DFT) the intrinsic magnetic properties of a promising system, R(Fe1−xCox)11TiZ with R=Y, Ce and interstitial doping (Z=H,C,N). The magnetization M, Curie temperature TC, and magnetocrystalline anisotropy energy K calculated in local density approximation to DFT agree well with measurements. Site-resolved contributions to K reveal that all three Fe sublattices promote uniaxial anisotropy in YFe11Ti, while competing anisotropy contributions exist in YCo11Ti. As observed in experiments on R(Fe1−xCox)11Ti, we find a complex nonmonotonic dependence of K on Co content and show that anisotropy variations are a collective effect of MAE contributions from all sites and cannot be solely explained by preferential site occupancy. With interstitial doping, calculated TC enhancements are in the sequence of N\u3eC\u3eH, with volume and chemical effects contributing to the enhancement. The uniaxial anisotropy of R(Fe1−xCox)11TiZ generally decreases with C and N; although, for R=Ce, C doping is found to greatly enhance it for a small range of 0.
- …