Magnetic behavior of Fe(Se,Te) systems: First-principles calculations

Abstract:

The magnetic behaviors in Fe(Se,Te) systems have been investigated systematically using density functional calculations. At the experimental lattice parameters, the ground state is found to be in the double stripe magnetic phase for FeTe but in the single stripe magnetic phase for FeSe and FeSe0:5Te0:5, and there is no preference in the different easy axes of magnetization. Substitution ofSe by Te enlarges the size of the Fermi surface in FeSe0:5Te0:5, resulting in a stronger nestingeffect and thus enhancing the superconductivity. It is found that the double stripe order inFeTe1-xSexchanges to the single stripe order when x>0.18. Spiral calculations on FeSe0:5Te0:5show that the lowest energy is at the commensurate point~Q¼(0.5,0.5), accompanied by additional local minima at two incommensurate points near~Q¼(0.5,0.5). This observation is consistent with the experimentally observed positions of low energy magnetic excitations.Geometry optimization calculations show that the tetragonal cell relaxes to orthorhombic and monoclinic cells for FeSe and FeTe, respectively, but remains unchanged for FeSe0:5Te0:5.

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