Hydrothermal synthesis of Bi2Fe4O9 nanochains and study of their multiferroic coupling.

• We have successfully prepared Bi 2 Fe 4 O 9 nanochains. • It shows antiferromagnetic transition at ~63 K and surface ferromagnetism. • An exchange bias field of ~100 Oe has been observed. • It exhibits 77% change in ferroelectric polarization at 10 kOe magnetic field. We report synthesis of self-assembled Bi 2 Fe 4 O 9 nanochains by hydrothermal method using Oleic acid as a surfactant which plays an important role in the self-assembled nanochain formation. Temperature dependent dc magnetization study suggests downward shift of the Neel temperature T N ~ 63 K for the particles of size ~ 22 nm while it is reported to be ~ 260 K in the bulk sample. The magnetic hysteresis (M−H) loops offer evidence of weak ferromagnetism across the entire temperature range 10–300 K. Exchange coupling across the interface between coexisting ferromagnetic and antiferromagnetic orders gives rise to a small amount of exchange bias at low temperature. The sample also exhibits substantial magnetoelectric multiferroic coupling at room temperature with ~77% suppression of ferroelectric polarization under 10 kOe magnetic field. [ABSTRACT FROM AUTHOR]