  The effect of Ir substitution for Os in CeOs2Al10, with an unusually high
Neel temperature of T~28.5K, has been studied by high-resolution neutron
diffraction and magnetization measurements. A small amount of Ir (~ 8%) results
in a pronounced change of the magnetic structure of the Ce-sublattice. The new
magnetic ground state is controlled by the single ion anisotropy and implies
antiferromagnetic arrangement of the Ce-moments along the a-axis, as expected
from the anisotropy of the paramagnetic susceptibility. The value of the
ordered moments, 0.92(1) mu_B, is substantially bigger than in the undoped
compound, whereas the transition temperature is reduced down to 21K. A
comparison of the observed phenomena with the recently studied CeRu1.9Rh0.1Al10
system, exhibiting similar behaviour [A. Kondo et al., J. Phys. Soc. Jpn. 82,
054709 (2013)], strongly suggests the electron doping as the main origin of the
ground state changes. This provides a new way of exploring the anomalous
magnetic properties of the Ce(Ru/Os)2Al10 compounds.
