  Nowdays, multiferroic materials with magnetoelectric coupling have many
real-world applications in the fields of novel memory devices. It is
challenging is to create multiferroic materials with strongly coupled
ferroelectric and ferrimagnetic orderings at room temperature. The single
crystal of ferric selenide (Fe3Se4) shows type-II multiferroic due to the
coexistence of ferroelectric as well as magnetic ordering at room temperature.
We have investigated the lattice instability, electronic structure,
ferroelectric, ferrimagnetic ordering and transport properties of ferroelectric
metal Fe3Se4. The density of states shows considerable hybridization of Fe-3d
and Se-4p states near the Fermi level confirming its metallic behavior. The
magnetic moments of Fe cations follow a type-II ferrimagnetic and ferroelectric
ordering with a calculated total magnetic moment of 4.25 per unit cell
(Fe6Se8). The strong covalent bonding nature of Fe-Se leads to its
ferroelectric properties. In addition, the symmetry analysis suggests that
tilting of Fe sub-lattice with 3d-t2g orbital ordering is due to the
Jahn-Teller (JT) distortion. This study provides further insight in the
development of spintronics related technology using multiferroic materials.
