Neutron diffraction in MnSb2O6 : Magnetic and structural domains in a helicoidal polar magnet with coupled chiralities

Abstract

MnSb 2 O 6 is based on the structural chiral P321 space group No. 150 where the magnetic Mn 2+ moments (S = 5/2, L ≈ 0) order antiferromagnetically at T N = 12 K. Unlike the related iron based langasite (Ba 3 NbFe 3 Si 2 O 14 ) where the low-temperature magnetism is based on a proper helix characterized by a time-even pseudoscalar "magnetic" chirality, the Mn 2+ ions in MnSb 2 O 6 order with a cycloidal structure at low temperatures, described instead by a time-even vector "magnetic" polarity. A tilted cycloidal structure has been found [M. Kinoshita et al., Phys. Rev. Lett. 117, 047201 (2016)] to facilitate ferroelectric switching under an applied magnetic field. In this work, we apply polarized and unpolarized neutron diffraction analyzing the magnetic and nuclear structures in MnSb 2 O 6 with the aim of understanding this magnetoelectric coupling. We find no evidence for a helicoidal magnetic structure with one of the spin envelope axes tilted away from the cycloidal c axis. However, on the application of a magnetic field c the spin rotation plane can be tilted, giving rise to a cycloid-helix admixture that evolves towards a distorted helix (zero cycloidal component) for fields great than ≈2 T. We propose a mechanism for the previously reported ferroelectric switching based on coupled structural and magnetic chiralities requiring only an imbalance of structural chiral domains.

Understanding and Suppressing C–C Cleavage during Glycerol Oxidation for C3 Chemical Production

“…The precursor MnSb 2 O 6 film is composed of Sb metal and Mn­(OH) 2 with a 1:2 molar ratio, which react to form crystalline MnSb 2 O 6 during annealing in air at 700 °C . All the Mn sites in the MnSb 2 O 6 crystal structure are isolated from other Mn sites with a nearest Mn–Mn distance of ∼4.7 Å. , The scanning electron microscopy (SEM) images of the MnO 2 and MnSb 2 O 6 films used in this study are shown in Figures S1–S2. Other characterization results for MnO 2 and MnSb 2 O 6 are available elsewhere. , …”

“…33 All the Mn sites in the MnSb 2 O 6 crystal structure are isolated from other Mn sites with a nearest Mn−Mn distance of ∼4.7 Å. 36,37 To initially assess the activity of these films for water and glycerol oxidation at various pH conditions and determine which potentials should be used for constant potential glycerol oxidation, linear sweep voltammetry (LSV) was carried out at pH 1, 4, 7, 10, 13, and 14 (Figure 1). The intermediate pH conditions (4, 7, and 10) were buffered to maintain the pH throughout the experiments (see the Experimental Section for electrolyte preparation details).…”

“…Another critical difference between MnO x and MnSb 2 O 6 is that while each Mn site in the binary oxide MnO x is surrounded by other Mn sites via bridging O atoms (i.e., Mn−O−Mn) with a nearest Mn−Mn distance of ∼2.9 Å, 35 all the Mn sites in the ternary MnSb 2 O 6 are isolated from other Mn sites (i.e., no Mn−O−Mn linkage) with a nearest Mn−Mn distance of ∼4.7 Å. 36,37 We presume that C−C cleavage of a glycol moiety would require two nearby catalytic centers that can coordinate to the two adjacent alcohol groups to activate the C−C bond or stabilize the two intermediates resulting from C−C cleavage. Thus, we postulate that in MnSb 2 O 6 with no nearby Mn centers, C−C cleavage may be suppressed.…”

Magnetic structure of the swedenborgite compound CaBaMn2Fe2O7 derived by powder neutron diffraction and Mössbauer spectroscopy

“…To unambiguously relate the magnetic chirality to the structural chirality, the latter needs to be determined by analyzing the Schwinger scattering of adequate reflections (see, e.g., Refs. [31,32]). We have identified several reasonably strong (hkl) reflections revealing a flipping ratio asymmetry of |R − 1| > 0.04 which would be experimentally feasible.…”