Magnetic structure and multiferroicity of Sc-substituted hexagonal Yb Fe O 3

The hexagonal rare-earth ferrite $R\mathrm{Fe}{\mathrm{O}}_{3}$ family represents a unique class of multiferroics exhibiting weak ferromagnetism, and a strong coupling between magnetism and structural trimerization is predicted. However, the hexagonal structure for $R\mathrm{Fe}{\mathrm{O}}_{3}$ remains metastable in conventional conditions. We have succeeded in stabilizing the hexagonal structure of polycrystalline $\mathrm{Yb}\mathrm{Fe}{\mathrm{O}}_{3}$ by partial Sc substitution of Yb. Using bulk magnetometry and neutron diffraction, we find that ${\mathrm{Yb}}_{0.42}{\mathrm{Sc}}_{0.58}\mathrm{Fe}{\mathrm{O}}_{3}$ orders into a canted antiferromagnetic state with the N\'eel temperature ${T}_{N}\ensuremath{\sim}165\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, below which the ${\mathrm{Fe}}^{3+}$ moments form the triangular configuration in the $ab$ plane and their in-plane projections are parallel to the [100] axis, consistent with magnetic space group $P{6}_{3}{c}^{\ensuremath{'}}{m}^{\ensuremath{'}}$. It is determined that the spin canting is aligned along the $c$ axis, giving rise to the weak ferromagnetism. Furthermore, the ${\mathrm{Fe}}^{3+}$ moments reorient toward a new direction below reorientation temperature ${T}_{R}\ensuremath{\sim}40\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, satisfying magnetic subgroup $P{6}_{3}$, while the ${\mathrm{Yb}}^{3+}$ moments order independently and ferrimagnetically along the $c$ axis at the characteristic temperature ${T}_{\mathrm{Yb}}\ensuremath{\sim}15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Interestingly, reproducible modulation of electric polarization induced by magnetic field at low temperature is achieved, suggesting that the delicate structural distortion associated with two-up/one-down buckling of the Yb/Sc planes and tilting of the $\mathrm{Fe}{\mathrm{O}}_{5}$ bipyramids may mediate the coupling between ferroelectric and magnetic orders under magnetic field. The present work represents substantial progress to search for high-temperature multiferroics in hexagonal ferrites and related materials.