Magnetic transition and spin rotation in a new multiferroic Ba 3 TaFe 3 Si 2 O 14 observed by the M?ssbauer spectroscopy

摘要

The long-range 3D magnetic ordering in the Fe ~(3+) -containing langasite family compound Ba _3 TaFe_3 Si _2 O _(14) 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 P 321→ P 3 induced by the magnetic ordering. At this transition, the presence of the polar threefold axis creates the conditions for the ferroelectric state and Ba _3 TaFe_3 Si_2 O_(14) may be considered as a magnetically induced multiferroic. The Fe~(3+) 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.