Disorder-Driven Spin-Reorientation in Multiferroic $h-YMn_{1-x}Fe_xO_3$

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.