Effect of doping and pressure on magnetism and lattice structure of Fe-based superconductors

Abstract

Using first principles calculations, we analyze structural and magnetic trends as a function of charge doping and pressure in BaFe${}_2$As${}_2$, and compare to experimentally established facts. We find that density functional theory, while accurately reproducing the structural and magnetic ordering at ambient pressure, fails to reproduce some structural trends as pressure is increased. Most notably, the Fe-As bondlength which is a gauge of the magnitude of the magnetic moment, $\mu$, is rigid in experiment, but soft in calculation, indicating residual local Coulomb interactions. By calculating the magnitude of the magnetic ordering energy, we show that the disruption of magnetic order as a function of pressure or doping can be qualitatively reproduced, but that in calculation, it is achieved through diminishment of $|\mu |$, and therefore likely does not reflect the same physics as detected in experiment. We also find that the strength of the stripe order as a function of doping is strongly site-dependent: magnetism decreases monotonically with the number of electrons doped at the Fe site, but increases monotonically with the number of electrons doped at the Ba site. Intra-planar magnetic ordering energy (the difference between checkerboard and stripe orderings) and interplanar coupling both follow a similar trend. We also investigate the evolution of the orthorhombic distortion, $e=(a-b)/(a+b),$ as a function of $\mu$, and find that in the regime where experiment finds a linear relationship, our calculations are impossible to converge, indicating that in density functional theory, the transition is first order, signalling anomalously large higher order terms in the Landau functional.

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Cited by in corpus (19)

• Structural collapse and superconductivity in rare earth-doped CaFe2As2
• Strong Pressure Dependent Electron-Phonon Coupling in FeSe
• High-pressure flux growth, structural, and superconducting properties of LnFeAsO (Ln = Pr, Nd, Sm) single crystals
• Symmetry preserving lattice collapse in tetragonal SrFe_(2-x)Ru_xAs_2 (x = 0, 0.2) -- a combined experimental and theoretical study
• Co-substitution effects on the Fe-valence in the BaFe2As2 superconducting compound: A study of hard x-ray absorption spectroscopy
• Pressure versus concentration tuning of the superconductivity in Ba(Fe(1-x)Cox)2As2
• Phonon softening near structural transition in BaFe2As2 observed by inelastic x-ray scattering
• Complex structures of different CaFe${}_2$As${}_2$ samples
• Metal-Insulator Transition and the Role of Electron Correlation in FeO2
• Pressure and chemical substitution effects in the local atomic structure of BaFe2As2
• Structural origin of the anomalous temperature dependence of the local magnetic moments in the CaFe${}_2$As${}_2$ family of materials
• van der Waals interaction in iron-chalcogenide superconductors
• Spin-state Crossover Model for the Magnetism of Iron Pnictides
• First Principles Study of CaFe2As2 "Collapse" Under Pressure
• Quasiparticle interference in antiferromagnetic parent compounds of Fe-based superconductors
• Lifshitz Transitions in 122-Pnictides Under Pressure
• Parallel suppression of superconductivity and Fe moment in the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 under pressure
• Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2
• Lattice Disorder Effect on Magnetic Ordering of Iron Arsenides