Magnetic properties of iron pnictides from spin-spiral calculations

Abstract

The wave-vector (q) and doping dependences of the magnetic energy, iron moment, and effective exchange interactions in LaFeAsO, BaFe2As2, and SrFe2As2 are studied by self-consistent LSDA calculations for co-planar spin spirals. For the undoped compounds, the calculated total energy, E(q), reaches its minimum at q corresponding to stripe anti-ferromagnetic (AF) order. In LaFeAsO, this minimum becomes flat already at low levels of electron-doping and shifts to an incommensurate q at δ=0.2, where δ is the number of additional electrons (δ > 0) or holes (S < 0) per Fe. In BaFe2As2 and SrFe2As2, stripe order remains stable for hole doping down to δ = −0.3. Under electron doping, on the other hand, the E(q) minimum shifts to incommensurate q already at δ=0.1.