  We report perturbed angular correlation measurements with 111mCd/111Cd and
111In/111Cd probes, at the ISOLDE-CERN facility, in the manganite compounds
BaMnO3 , with the 6H and 15R polymorphs, and SrMnO3 , with the 4H polymorph.
The electric field gradient (EFG) is measured, and found approximately constant
in a large temperature range for all the compounds. The EFG is also calculated
from first principles with density functional theory, and compared with
experimental results by considering diluted substitutional Cd impurities. Based
on the results, we assign as sites for the probes the Ba (for BaMnO3-6H, 15R)
and Sr (for SrMnO3-4H) sites, apart from fractions of undetermined origin in
the case of BaMnO3-6H. We predict the hyperfine parameters in the recently
synthesized multiferroic manganite Sr0.5Ba0.5MnO3 , and its variation with the
structure and electric polarization, which is found to be very small.
