  It is currently understood that high temperature superconductivity (SC) in
the transition metal $(M)$ substituted iron arsenides
Ba(Fe$_{1-x}$$M$$_{x}$)$_{2}$As$_{2}$ is promoted by magnetic excitations with
wave vectors $(\pi,0)$ or $(0,\pi)$. It is known that while a small amount of
Co substitution leads to SC, the same does not occur for Mn for any value of
$x$. In this work, magnetic excitations in the iron arsenides
Ba(Fe$_{1-x}$Mn$_{x}$)$_{2}$As$_{2}$ ($x=0.0$, $0.007$, $0.009$, $0.08$) are
investigated by means of Resonant Inelastic X rays Scattering (RIXS) at the Fe
$L_{3}$-edge, for momentum transfer $\boldsymbol{q}$ along the high symmetry
Brillouin zone $(\pi,0)$ and $(\pi,\pi)$ directions. It is shown that with
increasing Mn content ($x$), the excitations become anisotropic both in
dispersion and lineshape. Both effects are detected even for small values of
$x$, evidencing a cooperative phenomenon between the Mn impurities, that we
ascribe to emerging N\'eel order of the Mn spins. Moreover, for $x=0.08$, the
excitations along $\boldsymbol{q}\parallel(\pi,0)$ are strongly damped and
nearly non dispersive. This result suggests that phases of arsenides containing
local moments at the FeAs layers, as in Mn or Cr substituted phases, do not
support high temperature SC due to absence of the appropriate magnetic
excitations.
