Mössbauer Spectroscopy of Ferroelectric YMn2O5

We have investigated Mossbauer spectra of single crystal YMn 2 O 5 (with 1.5 mol % 57 Fe), which is simultaneously ferroelectric (the ferroelectric Curie temperature T CE =39 K and the second dielectric transition temperature T C2 =19 K) and antiferromagnetic ( T N =45 K) at low temperatures. In the temperature range of T C2 < T < T CE , the spectrum is composed of two different hyperfine sextets, indicating that the magnetic moments of Mn 3+ ions are in two different states. A half of them are oriented parallel to the a -direction, which is probably the easy direction, while the other half are forced to be oriented along the bisector of the b - and c -direction. A few evidences indicate that both A and B moments rotate at T C2 to form an incommensurate helical spin structure with bunching. We present a remark on a possible relation between the ferroelectric transition and the magnetic long-range order in this oxide.