  We report on microscopic study of the ferromagnetism enhancement in the Ru
doped ferromagnetic superconductor (FM SC) UCoGe. For that purpose, two single
crystals with composition UCo0.97Ru0.03Ge and UCo0.88Ru0.12Ge were prepared.
Both single crystals were investigated by polarized neutron diffraction (PND)
at low temperatures in magnetic fields and the latter one also by the soft
X-ray magnetic circular dichroism (XMCD) method. UCo0.96Ru0.03Ge and
UCo0.88Ru0.12Ge have been found ordering ferromagnetically below the Curie
temperature TC = 6 K and 8.5 K, respectively, which are considerable higher
than TC = 3 K of UCoGe. The increase of TC is accompanied by enhancement of the
spontaneous moment to ms = 0.11 mB/f.u. and ms = 0.21 mB/f.u., respectively.
The analysis of the PND results assigns the ferromagnetism enhancement mainly
to the growth of the orbital part of uranium 5 f moment. In contrast to the
published results of PND study of the parent UCoGe, we have found parallel
orientation of the U and Co moments in both doped compounds. Evolution of
magnetic characteristics with Ru concentration is discussed within a scenario
considering the varying 5 f-ligand hybridization as the key mechanism.
