Mn3MnNb2O9: high-pressure triple perovskite with 1 : 2 B-site order and modulated spins.

The first triple perovskite with Mn in A- and 1 : 2 B-site order Mn3MnNb2O9, prepared using high pressure phase transformation of the magnetodielectric Mn4Nb2O9, is reported herein. It has a complex magnetic behaviour with a transition from a collinear AFM into an evolving incommensurate spin density wave (SDW) further stabilised into a lock-in structure dictated by the B-site order.