Structural Anomalies and Multiferroic Behavior in Magnetically FrustratedTbMn2O5

We have studied the magnetostructural phase diagram of multiferroic ${\mathrm{T}\mathrm{b}\mathrm{M}\mathrm{n}}_2{\mathrm{O}}_5$ as a function of temperature and magnetic field by neutron diffraction. Dielectric and magnetic anomalies are found to be associated with steps in the magnetic propagation vector, including a rare example of a commensurate-incommensurate transition on cooling below 24 K, and in the structural parameters. The geometrically frustrated magnetic structure is stabilized by “canted antiferroelectric” displacements of the ${\mathrm{M}\mathrm{n}}^{3+}$ ions, an example of the magnetic Jahn-Teller effect. The Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.