Magnetic transition and spin rotation in a new multiferroic Ba

The long-range 3D magnetic ordering in the Fe3+-containing langasite family compound Ba3TaFe3Si2O14 was observed below 27 K with the iron lattice split into two nonequivalent magnetic sublattices. The appearance of the nonequivalent Fe sites is associated with the structural phase transition P321→P3 induced by the magnetic ordering. At this transition, the presence of the polar threefold axis creates the conditions for the ferroelectric state and Ba3TaFe3Si2O14 may be considered as a magnetically induced multiferroic. The Fe3+ magnetic moments in the two sublattices are oriented at different angles to the local crystal axes with a mean value ∼45°. At temperatures between 4.2 and 25 K, iron spins in two sublattices rotate in opposite directions which can be related to the magnetic chirality in the helicoidal magnetic structure