  The (Li$_{1-x}$Fe$_{x}$OH)FeSe superconductor has been suspected to exhibit
long-range magnetic ordering due to Fe substitution in the LiOH layer. However,
no direct observation such as magnetic reflection from neutron diffraction has
be reported. Here, we use a chemical design strategy to manipulate the doping
level of transition metals in the LiOH layer to tune the magnetic properties of
the (Li$_{1-x-y}$Fe$_{x}$Mn$_{y}$OD)FeSe system. We find Mn doping exclusively
replaces Li in the hydroxide layer resulting in enhanced magnetization in the
(Li$_{0.876}$Fe$_{0.062}$Mn$_{0.062}$OD)FeSe superconductor without
significantly altering the superconducting behavior as resolved by magnetic
susceptibility and electrical/thermal transport measurements. As a result,
long-range magnetic ordering was observed below 12 K with neutron diffraction
measurements. This work has implications for the design of magnetic
superconductors for the fundamental understanding of superconductivity and
magnetism in the iron chalcogenide system as well as exploitation as functional
materials for next generation devices.
