MnTaO2N: polar LiNbO3-type oxynitride with a helical spin order

Cédric Tassel; Yoshinori Kuno; Yoshihiro Goto; Takafumi Yamamoto; Craig M Brown; James Hester; Koji Fujita; Masanobu Higashi; Ryu Abe; Katsuhisa Tanaka; Yoji Kobayashi; Hiroshi Kageyama

doi:10.1002/anie.201408483

MnTaO2N: polar LiNbO3-type oxynitride with a helical spin order

Angew Chem Int Ed Engl. 2015 Jan 7;54(2):516-21. doi: 10.1002/anie.201408483. Epub 2014 Nov 21.

Authors

Cédric Tassel¹, Yoshinori Kuno, Yoshihiro Goto, Takafumi Yamamoto, Craig M Brown, James Hester, Koji Fujita, Masanobu Higashi, Ryu Abe, Katsuhisa Tanaka, Yoji Kobayashi, Hiroshi Kageyama

Affiliation

¹ Graduate School of Engineering, Kyoto University, Kyoto 615-8510 (Japan); The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8501 (Japan).

PMID: 25417894
DOI: 10.1002/anie.201408483

Abstract

The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO2N 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 MnTaO2N adopts the LiNbO3-type structure, with a random distribution of O(2-) and N(3-) anions. MnTaO2N 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 LiNbO3-type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO4N2 octahedral network combined with the mixed O(2-)/N(3-) species that results in a distribution of (super)-superexchange interactions.

Keywords: helical spin order; high-pressure chemistry; magnetic oxynitrides; mixed anion phases; transition metals.