Theoretical investigation of the electronic and magnetic properties of the orthorhombic phase ofBa(Fe1−xCox)2

Abstract

We present a comprehensive study on the low-temperature orthorhombic phase of Ba(Fe 1-x Co x ) 2 As 2 based on the Korringa-Kohn-Rostoker-Green function approach. Using this bandstructure method in combination with the coherent potential approximation alloy theory we are able to investigate the evolution of the magnetic and electronic properties of this prototype iron pnictide for arbitrary concentrations x, while dealing with the chemical disorder without uncontrolled simplifications by using solely a rigid band shift or the virtual crystal approximation. We discuss the development of the site resolved magnetic moments for the experimentally observed stripe antiferromagnetic order together with the strong electronic anisotropy of the Fermi surface and compare it with angle-resolved photoemission spectroscopy measurements of detwinned crystals. We furthermore calculate magnetic exchange coupling parameters Jij and use them for Monte-Carlo simulations on the basis of the classical Heisenberg model to get an insight on the temperature dependence of the magnetic ordering on the cobalt concentration.

Hyperfine fields in the BaFe2As2 family and their relation to the magnetic moment

“…This interpolation was individually done for each type of substitution, based on available experimental data [9,[38][39][40][41][42]. More details on this procedure can be found in previous publications [28,29]. The treatment of disorder introduced by substitution is dealt with by means of the CPA.…”

“…These include electron doping in the case of Ba(Fe 1−x Co x ) 2 As 2 and Ba(Fe 1−x Ni x ) 2 As 2 , hole doping as in (Ba 1−x K x )Fe 2 As 2 and also isovalently doped compounds like Ba(Fe 1−x Ru x ) 2 As 2 and BaFe 2 (As 1−x P x ) 2 . To deal adequately with substitutional systems the fully relativistic Korringa-KohnRostoker-Green function (KKR-GF) approach is used, which was already shown to be an appropriate tool to investigate various properties of the iron pnictides [28][29][30]. Chemical disorder due to substitution is dealt by means of the coherent potential approximation (CPA), which effectively gives results comparable to the tedious average over many supercell configurations and is much more reliable than the virtual crystal approximation (VCA) [28,31].…”

“…To deal adequately with substitutional systems the fully relativistic Korringa-KohnRostoker-Green function (KKR-GF) approach is used, which was already shown to be an appropriate tool to investigate various properties of the iron pnictides [28][29][30]. Chemical disorder due to substitution is dealt by means of the coherent potential approximation (CPA), which effectively gives results comparable to the tedious average over many supercell configurations and is much more reliable than the virtual crystal approximation (VCA) [28,31]. Application of the CPA to the iron pnictides was already shown to be quite successful [28,29,[32][33][34].…”

“…Chemical disorder due to substitution is dealt by means of the coherent potential approximation (CPA), which effectively gives results comparable to the tedious average over many supercell configurations and is much more reliable than the virtual crystal approximation (VCA) [28,31]. Application of the CPA to the iron pnictides was already shown to be quite successful [28,29,[32][33][34]. Using this approach, one cannot only investigate the type-resolved evolution of magnetic moments with composition, but also the doping dependence of the hyperfine fields.…”

Charge doping versus impurity scattering in chemically substituted iron pnictides

“…From the viewpoint of electronic structure calculations this dichotomy between localized extra electrons and doping into conduction bands has been first addressed by supercell calculations [5,6]. More recently, effective medium approaches, which can handle arbitrary impurity concentrations, have been used to study the effect of substitutional disorder on bandstructure and Fermi surface topology [7,8]. Nevertheless a systematic first principles investigation of different substitutions on the behavior of electronic quasiparticles is still lacking.A further aspect of substitutional disorder is its impact on the superconducting state.…”