Regensburg 2010 – scientific programme

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MA: Fachverband Magnetismus

MA 30: Electron Theory of Magnetism

MA 30.3: Talk

Thursday, March 25, 2010, 17:30–17:45, H22

Theoretical study of the stability of AFM order in iron pnictides — •Alexander Yaresko — Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart, Germany

The wave-vector (q) and doping (δ) dependences of the total energy, E(q), in electron (δ>0) doped LaFeAsO_1−xF_x and M(Fe_1−xCo_x)₂As₂ and hole (δ<0) doped M_1−xK_xFe₂As₂ (M=Ba, Sr) are studied by performing self-consistent LSDA calculations for co-planar spin spirals using the LMTO method. For the undoped compounds the minimum of E(q) is found at q=(π,0) corresponding to stripe AFM order with the Fe magnetic moment of about 1.5µ_B. In LaFeAsO_1−xF_x the minimum shifts to an incommensurate q already at δ=0.1 (x=0.1). Similar behavior is also found when FeAs layers in M(Fe_1−xCo_x)₂As₂ are doped with electrons. In contrast, stripe AFM order in M_1−xK_xFe₂As₂ remains stable in a wide range of hole doping up to δ=−0.3, which corresponds to the K content x=0.6, although the stabilization energy of the AFM solution rapidly decreases with doping. Spin-spiral calculations for LiFeAs predict a magnetic ground state with q=(π,0) but with the Fe moment (0.6µ_B) and the stabilization energy which are significantly smaller than in the other two families of Fe pnictides.

According to the calculated q_z dependence of the total energy, the magnetic interactions in LaFeAsO are 2D-like, whereas in MFe₂As₂ compounds FeAs layers are coupled antiferromagnetically, with the coupling in SrFe₂As₂ being stronger than in BaFe₂As₂.