Mössbauer Spectrum and Spin Structure of Weakly Ferroelectric YMn 2 O 5 and HoMn 2 O 5

Rare earth (R) manganese oxides RMn 2 O 5 are the ferroelectric crystals with Curie temperature between 25 and 39 K. They are at the same time antiferromagnetic below the Neel temperature slightly above their ferroelectric transition temperature. By applying Mossbauer spectroscopy to the samples with a small amount of 57 Fe, we concluded that Mn 3+ ions in ferroelectric YMn 2 O 5 and HoMn 2 O 5 are classified into two groups with different magnetic environments. We suggest a possibility that the long-range magnetic structure induces the spontaneous polarization.