Nonferroelectric phase with loss of cycloidal magnetic structure in Tb0.515Gd0.485Mn2 O5

Neutron-scattering measurements were employed to investigate the magnetic ordering in Tb1-xGdxMn2O5 (x=0.485) enriched with the Gd160 isotope, a member of multiferroic RMn2O5 (R=rare-earth element) compounds. This material, at low temperatures, exhibits commensurate magnetic (CM) ordering, which drives electric polarization. Notably, electric polarization diminishes as the temperature decreases further, while the CM ordering persists. Magnetic structure analyses revealed that a cycloidal magnetic structure along the c axis transforms into a sinusoidal-like structure, resulting in the nonferroelectric phase, whereas a collinear magnetic structure in the ab plane exhibits no significant change. The findings suggest that the cycloidal magnetic structure plays a key role in inducing electric polarization in the CM ordering of the present material.