title: Collinear to spiral spin transformation without changing the modulation wavelength upon ferroelectric transition in Tb1-xDyxMnO3.
abstract: Lattice modulation and magnetic structures in magnetoelectric compounds Tb1-xDyxMnO3 have been studied around the ferroelectric (FE) Curie temperature TC by x-ray and neutron diffraction. Temperature-independent modulation vectors through TC are observed for the compounds with 0.50 <or=x<or=0.68. This indicates that ferroelectricity with a polarization (P) along the c axis in the RMnO3 series cannot be ascribed to such an incommensurate-commensurate transition of an antiferromagnetic order as was previously anticipated. A neutron diffraction study with x=0.59 shows that the FE transition is accompanied by the transformation of the Mn-spin alignment from sinusoidal (collinear) antiferromagnetism into a transverse-spiral structure. The observed spiral structure below TC is expected to produce P along the c axis with the "inverse" Dzialoshinski-Moriya interaction, which is consistent with observation.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Arima
authors.forename: A
authors.initials: A
authors.lastname: Tokunaga
authors.forename: T
authors.initials: T
authors.lastname: Goto
authors.forename: H
authors.initials: H
authors.lastname: Kimura
authors.forename: Y
authors.initials: Y
authors.lastname: Noda
authors.forename: Y
authors.initials: Y
authors.lastname: Tokura