Abstract
The appearance of unconventional superconductivity often requires the suppression
of an antiferromagnetic (AFM) ordered state by tuning the chemical composition.
In BaFe2As2, the AFM ordered state is driven by Fermi surface nesting, resulting in
stripe magnetic ordering with propagation vector Qstripe = (; 0) (in Fe square lattice
notation). Co substitution acts as an electron donor that destabilizes the nesting
condition,1 leading to suppression of the stripe AFM ordering2 and the appearance of
superconductivity.3,4 Mn is nominally the hole-doping counterpart of Co which should
also detune the Fermi surface nesting, but it is not a superconductor.5 Here we report
that Mn doping does not act solely as a hole donor, but instead introduces strong spin
uctuations at a wavevector (; ) that is unrelated to the Fermi surface topology of
BaFe2As2. Spin
uctuations at (; ) and (; 0) coexist, suggesting the Mn dopants
act as local magnetic impurities that polarize neighbouring Fe/Mn spins, potentially
disrupting superconductivity.
