Ordered aeschynite-type polar magnets RFeWO6 ( R=Dy , Eu, Tb, and Y): A new family of type-II multiferroics

Abstract

We report the discovery of magnetoelectric multiferroicity in a family of oxides, $R\mathrm{FeW}{\mathrm{O}}_{6}$ ($R=\mathrm{Dy}$, Eu, Tb, and Y) that crystallize in a polar aeschynite-type structure ($Pna{2}_{1}$) with an ordered arrangement of $\mathrm{F}{\mathrm{e}}^{3+}$ and ${\mathrm{W}}^{6+}$ ions. Magnetization and analysis of neutron-diffraction data of $\mathrm{DyFeW}{\mathrm{O}}_{6}$ reveal a commensurate noncollinear antiferromagnetic ordering of $\mathrm{F}{\mathrm{e}}^{3+}$ spins (${T}_{\mathrm{N}}^{\mathrm{Fe}}\ensuremath{\sim}18\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), which induce Dy spins to order at the same temperature. A sudden change in electric polarization $(\mathrm{\ensuremath{\Delta}}P)$ appears in all the compounds at ${T}_{\mathrm{N}}^{\mathrm{Fe}}=15--18\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The electric polarization is sensitive to an applied magnetic field, and the coupling between different magnetic $R$-ion and Fe-ion moments suppresses the polarization to a different extent. Although the measured polarization in polycrystalline $\mathrm{DyFeW}{\mathrm{O}}_{6}$ at 3.5 K is about $3\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$, a simple calculation of the ionic contribution to polarization with formal charges is $75\phantom{\rule{0.16em}{0ex}}560\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ and it is of the form $\mathbf{P}=({p}_{x},0,{p}_{z})$ where, ${p}_{x}$ comes from magnetic ordering and ${p}_{z}$ is associated with the polar structure in the paramagnetic state. These findings open up an avenue to explore further new polar magnets with rare-earth/transition-metal ions in the ordered aeschynite-type structure.