Relation between ferroelectric and antiferromagnetic order in RMn2O5

RMn2O5 (R=Y and rare earth) shows successive magnetic and ferroelectric phase transitions at about 45, 40, 39, 20 and 10 K. We have reinvestigated the magnetic structure of YMn2O5 at the commensurate phase (T=25K) using a single crystal four-circle diffractometer in order to discuss the mechanism of magnetoelectric interaction and the origin of ferroelectricity. We also observed the lattice modulation vectors (qL) to compare the magnetic propagation vectors (qM) by synchrotron X-ray diffraction. Improved magnetic structure data are compared with the theory recently proposed.