  Magnetic structure evolution of multiferroic hexagonal $YMn_{1-x}Fe_{x}O_{3}$
(${x} = 0, 0.05,$ and $0.1$) has been studied by carrying out detailed
temperature-dependent neutron diffraction at zero- and 5T-fields. Thermodynamic
data confirm antiferromagnetic ordering at $T_{N}$ in all the compositions. Our
sub-$T_{N}$ neutron diffraction results assign the magnetic structure of pure
$YMnO_3$ to $\Gamma_{1}$ irreducible representation. Over the
perturbative-doping range, the magnetic configuration changes via
$\Gamma_{1}+\Gamma_{2}$ for $YMn_{0.95}Fe_{0.05}O_{3}$ on to $\Gamma_{2}$ for
$YMn_{0.9}Fe_{0.1}O_{3}$, as the maiden compositional analogue of
spin-reorientation; its occurrence in temperature-domain already reported for
several manganites. Moreover, while the large thermal isostructural changes
observed above ${T}_{N}$ are subdued in the ordered state, small alterations by
the applied 5T-field are relatively uniform across, confirming strong
magneto-elastic nature of the system. Decrease of the ordered magnetic moment
($\mu_{ord}$) and planar magnetic frustration noted with Fe-doping is enhanced
by the applied field, apparently through canting.
