Fe4Nb2O9: A magnetoelectric antiferromagnet

The structural, magnetic, and electrical properties of a Fe4Nb2O9 polycrystalline sample have been characterized. It is found that this compound crystallizes in the P (3) over bar c1 space group of the alpha-Al2O3 structure and is thus isostructural to Co4Nb2O9 and Mn4Nb2O9, two linear magnetoelectric oxides. But in marked contrast, its epsilon' (T) curve reveals two broad transitions at T-N1 congruent to 90K and T-N2 congruent to 77K, the former corresponding to the antiferromagnetic ordering temperature. Below T-N1, the M(H) magnetization curves reveal the existence of spin flop at about 6 T. In this temperature region, a H-induced electric polarization for mu H-0 > 6 T is evidenced by both sets of I-p(T)(H) and P(H)(T) curves. All these results point towards Fe4Nb2O9 being a magnetoelectric member of the A(4)B(2)O(9) family (A = Mn, Fe, Co and B = Nb, Ta).