MnTaO 2 N: Polar LiNbO 3 ‐type Oxynitride with a Helical Spin Order

The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO 2 N are reported. High‐pressure synthesis at 6 GPa and 1400 °C allows for the stabilization of a high‐density structure containing middle‐to‐late transition metals. Synchrotron X‐ray and neutron diffraction studies revealed that MnTaO 2 N adopts the LiNbO 3 ‐type structure, with a random distribution of O 2− and N 3− anions. MnTaO 2 N with an “orbital‐inactive” Mn 2+ ion (d 5 ; S =5/2) exhibits a nontrivial helical spin order at 25 K with a propagation vector of [0,0,δ] ( δ ≈0.3), which is different from the conventional G‐type order observed in other orbital‐inactive perovskite oxides and LiNbO 3 ‐type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO 4 N 2 octahedral network combined with the mixed O 2− /N 3− species that results in a distribution of (super)‐superexchange interactions.