title: MnTaO2N: polar LiNbO3-type oxynitride with a helical spin order.
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.
authors.affiliation: Graduate School of Engineering, Kyoto University, Kyoto 615-8510 (Japan); The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8501 (Japan).
authors.forename: Cédric
authors.initials: C
authors.lastname: Tassel
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kuno
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Goto
authors.forename: Takafumi
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Craig M
authors.initials: CM
authors.lastname: Brown
authors.forename: James
authors.initials: J
authors.lastname: Hester
authors.forename: Koji
authors.initials: K
authors.lastname: Fujita
authors.forename: Masanobu
authors.initials: M
authors.lastname: Higashi
authors.forename: Ryu
authors.initials: R
authors.lastname: Abe
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Tanaka
authors.forename: Yoji
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kageyama
keywords: helical spin order; high-pressure chemistry; magnetic oxynitrides; mixed anion phases; transition metals