Synchrotron diffraction as a function of temperature and pressure, specific heat, magnetic susceptibility and small-angle neutron scattering experiments have revealed an anomalous response of MnGe. Similar but less pronounced behavior has also been observed in Mn1−xCoxGe and Mn1−xFexGe solid solutions. Spin density fluctuations and Mn spin state instability are discussed as possible candidates for the observed effects.

MSbO compounds (M = Mg, Co, Ni, Cu, Zn) are known in the tetragonal trirutile forms, slightly distorted monoclinically with M = Cu due to the Jahn-Teller effect. In this study, using a low-temperature exchange reaction between ilmenite-type NaSbO and molten MSO-KCl (or MgCl-KCl) mixtures, these five compositions were prepared for the first time as trigonal layered rosiaite (PbSbO)-type phases. Upon heating, they irreversibly transform to the known phases via amorphous intermediates, in contrast to previously studied isostructural MnSbO, where the stable phase is structurally related to the metastable phase. The same method was found to be applicable for preparing stable rosiaite-type CdSbO. The formula volumes of the new phases show an excellent correlation with the ionic radii (except for M = Cu, for which a Jahn-Teller distortion is suspected) and are 2-3% larger than those for the known forms although all coordination numbers are the same. The crystal structure of CoSbO was refined via the Rietveld method: P3[combining macron]1m, a = 5.1318(3) Å, and c = 4.5520(3) Å. Compounds with M = Co and Ni antiferromagnetically order at 11 and 15 K, respectively, whereas the copper compound does not show long-range magnetic order down to 1.5 K. A comparison between the magnetic behavior of the metastable and stable polymorphs was carried out. FeSbO could not be prepared because of the 2Fe + Sb = 2Fe + Sb redox reaction. This electron transfer produces an additional 5s shell for Sb and results in a volume increase. A comparison of the formula volume for the stable mixture FeSbO + 0.5SbO with that extrapolated for FeSbO predicted that the trirutile-type FeSbO can be stabilized at high pressures.

Neutron diffraction rejects the prismatic P6̄2m model with Mn/Te disorder and proves the chiral structure with octahedral coordination for all cations.

No abstract

MnSnTeO 6 , a new chiral antiferromagnet, was prepared both by topotactic transformation of the metastable rosiaite-type polymorph and by direct synthesis from coprecipitated hydroxides. Its structure, static and dynamic magnetic properties were studied comprehensively both experimentally (through X-ray and neutron powder diffraction, magnetization, specific heat, dielectric permittivity and ESR techniques) and theoretically (by means of ab initio density functional theory (DFT) calculations within the spin-polarized generalized gradient approximation). MnSnTeO 6 is isostructural with MnSb 2 O 6 (space group P321) and does not show any structural transition between 3 and 300 K. The magnetic susceptibility and specific heat exhibit an antiferromagnetic ordering at T N ≈ 9.8 K, which is confirmed by low-temperature neutron data. At the same time, the thermodynamic parameters demonstrate an additional anomaly on the temperature dependences of magnetic susceptibility (T), specific heat C p (T) and dielectric permittivity (T) at T *  4.9 K, which is characterized by significant temperature hysteresis. Clear enhancement of the dielectric permittivity at T * is most likely to reflect the coupling of dielectric and magnetic subsystems leading to development of electric polarization. It was established that the ground state of MnSnTeO 6 is stabilized by seven exchange parameters, and neutron diffraction revealed incommensurate magnetic structure with propagation vector k= (0, 0, 0.183) analogous to that of MnSb 2 O 6 . Ab initio DFT calculations demonstrate that the strongest exchange coupling occurs between planes along diagonals. All exchange parameters are antiferromagnetic and reveal moderate frustration.