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

The hyperfine field B-hf and the magnetic properties of the BaFe2As2 family are studied using the fully relativistic Dirac formalism for different types of substitution. The study covers electron doped Ba(Fe1-xCox)(2)As-2 and Ba(Fe1-xNix)(2)As-2, hole doped (Ba1-xKx)Fe2As2, and also isovalently doped Ba(Fe1-xRux)(2)As-2 and BaFe2(As1-xPx)(2) for a wide range of the concentration x. For the substituted compounds the hyperfine fields show a very strong dependence on the dopant type and its concentration x. Relativistic contributions were found to have a significantly stronger impact for the iron pnictides when compared to bulk Fe. As an important finding, we demonstrate that it is not sensible to relate the hyperfine field B-hf to the average magnetic moment mu of the compound, as it was done in earlier literature.