Magnetic transition and spin rotation in a new multiferroic Ba₃TaFe₃Si₂O₁₄ observed by the Mössbauer spectroscopy

¹ Shubnikov Institute of Crystallography, Russian Academy of Sciences - 119333, Moscow, Russia
² Moscow State University, Physical Department - 119992 Moscow, Russia

lyubutin@ns.crys.ras.ru

Received: 8 April 2010
Accepted: 10 June 2010

Abstract

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.