  The EuFe(2-x)Ni(x)As2 compounds exhibiting 3d and/or 4f magnetic order were
investigated by means of 57Fe and 151Eu M\"ossbauer spectroscopy. Additionally,
results for the end members of this system, i.e. EuFe2As2 and EuNi2As2, are
reported for comparison. It was found that spin-density-wave order of the Fe
itinerant moments is monotonically suppressed by Ni-substitution. However, the
3d magnetic order survives at the lowest temperature up to at least x = 0.12
and it is certainly completely suppressed for x = 0.20. The Eu localized
moments order regardless of the Ni concentration, but undergo a spin
reorientation with increasing x from the alignment parallel to the a-axis in
the parent compound, toward c-axis alignment for x > 0.07. The change of the 4f
spins ordering from antiferromagnetic to ferromagnetic takes place
simultaneously with a disappearance of the 3d spins order what is the evidence
of a strong coupling between magnetism of Eu2+ ions and the conduction
electrons of [Fe(2-x)Ni(x)As2]2- layers. The Fe nuclei experience the
transferred hyperfine magnetic field due to the Eu2+ ordering for
Ni-substituted samples with x > 0.04, while the transferred field is
undetectable in EuFe2As2 and for compound with a low Ni-substitution level. It
seems that the 4f ferromagnetic component arising from a tilt of the Eu2+
moments to the crystallographic c-axis leads to the transferred magnetic field
at the Fe atoms.
