713 research outputs found
The multiferroic phase of DyFeO:an ab--initio study
By performing accurate ab-initio density functional theory calculations, we
study the role of electrons in stabilizing the magnetic-field-induced
ferroelectric state of DyFeO. We confirm that the ferroelectric
polarization is driven by an exchange-strictive mechanism, working between
adjacent spin-polarized Fe and Dy layers, as suggested by Y. Tokunaga [Phys.
Rev. Lett, \textbf{101}, 097205 (2008)]. A careful electronic structure
analysis suggests that coupling between Dy and Fe spin sublattices is mediated
by Dy- and O- hybridization. Our results are robust with respect to the
different computational schemes used for and localized states, such as
the DFT+ method, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional and the
GW approach. Our findings indicate that the interaction between the and
sublattice might be used to tailor ferroelectric and magnetic properties of
multiferroic compounds.Comment: 6 pages, 4 figures-Revised versio
On the growth of ammonium nitrate(III) crystals
The growth rate of NH4NO3 phase III crystals is measured and interpreted using two models. The first is a standard crystal growth model based on a spiral growth mechanism, the second outlines the concept of kinetical roughening. As the crystal becomes rough a critical supersaturation can be determined and from this the step free energy. The step free energy versus temperature turns out to be well represented by a KosterlitzÂżThouless type model. Further a phenomenological treatment of some peculiar growth observations is given
Determining the Anisotropic Exchange Coupling of CrO_2 via First-Principles Density Functional Theory Calculations
We report a study of the anisotropic exchange interactions in bulk CrO_2
calculated from first principles within density functional theory. We determine
the exchange coupling energies, using both the experimental lattice parameters
and those obtained within DFT, within a modified Heisenberg model Hamiltonian
in two ways. We employ a supercell method in which certain spins within a cell
are rotated and the energy dependence is calculated and a spin-spiral method
that modifies the periodic boundary conditions of the problem to allow for an
overall rotation of the spins between unit cells. Using the results from each
of these methods, we calculate the spin-wave stiffness constant D from the
exchange energies using the magnon dispersion relation. We employ a Monte Carlo
method to determine the DFT-predicted Curie temperature from these calculated
energies and compare with accepted values. Finally, we offer an evaluation of
the accuracy of the DFT-based methods and suggest implications of the competing
ferro- and antiferromagnetic interactions.Comment: 10 pages, 13 figure
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