Preparation and characterization of metastable trigonal layered MSb2O6 phases (M = Co, Ni, Cu, Zn, and Mg) and considerations on FeSb2O6

Successive short- and long-range magnetic ordering in rosiaite-type CoGeTeO6 prepared by ion-exchange reaction

The missing member of the rosiaite family, CoGeTeO₆, was synthesized by mild ion-exchange reactions and characterized by magnetization M and specific heat C_p measurements. It exhibits a successive short- and long-range magnetic ordering at T_short-range ≈ 45 K and T_N = 15 K, respectively. Based on these measurements, the magnetic H-T phase diagram was established, showing two antiferromagnetic phases separated by a spin-flop transition. The reason why the pronounced short-range correlation occurs at a temperature nearly three times higher than T_N was found by evaluating the Co-O⋯O-Co exchange interactions using energy-mapping analysis. Although CoGeTeO₆ has a layered structure, its magnetic structure consists of three-dimensional antiferromagnetic lattices made up of rhombic boxes of Co²⁺ ions. The experimental data obtained at high temperatures agree well with the computational results by treating the Co²⁺ ions of CoGeTeO₆ as S = 3/2 ions, but the heat capacity and magnetization data were obtained at low temperatures by treating the Co²⁺ ion as a J_eff = 1/2 ion.

Chirality and Magnetocaloricity in GdFeTeO6 as Compared to GdGaTeO6

GdFeTeO₆ and GdGaTeO₆ have been prepared and their structures refined by the Rietveld method. Both are superstructures of the rosiaite type (space group P3¯1c). Their thermodynamic properties have been investigated by means of magnetization M and specific heat C_p measurements, evidencing the formation of the long-range antiferromagnetic order at T_N = 2.4 K in the former compound and paramagnetic behavior down to 2 K in the latter compound. Large magnetocaloric effect allows considering GdFeTeO₆ for the magnetic refrigeration at liquid hydrogen stage. Density functional theory calculations produce estimations of leading Gd–Gd, Gd–Fe and Fe–Fe interactions suggesting unique chiral 120° magnetic structure of Fe³⁺ (S = 5/2) moments and Gd³⁺ (J = 7/2) moments rotating in opposite directions (clockwise/anticlockwise) within weakly coupled layers of the rosiaite type crystal structure.

Significant magneto-elastic coupling at Griffiths-like phase boundaries in low dimensional oxides,ASb2O6(ANi and Mn)

The compounds, NiSb₂O₆(NSO) and MnSb₂O₆(MSO) attract the community for the quasi one-dimensional and layered structure composed of Ni²⁺and Mn²⁺, which orders antiferromagnetically atT_N= 6.7 and 12 K, respectively. Here, we report the Griffiths-like phase much aboveT_Nin the range of 37-85 K and 25-80 K for NSO and MSO, respectively. The dc magnetization results indicate the Griffiths-like phase, following the modified Curie-Weiss law. The magneto-capacitive responses for both the compounds show anomalies at the onset of the Griffiths-like phase. Intriguingly, the low temperature synchrotron diffraction results are conclusive for determining the singularities for both the compounds. Interplay between the low-dimensionality, magnetic frustration, and magneto-elastic coupling correlates the observed short range ordered state, which is suggested as a Griffiths-like phase, aboveT_Nfor both the compounds.

MnSnTeO6: A Chiral Antiferromagnet Prepared by a Two-Step Topotactic Transformation

MnSnTeO₆, 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 and its 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). MnSnTeO₆ is isostructural with MnSb₂O₆ (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 χ(T), specific heat C_p(T) and dielectric permittivity ε(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 MnSnTeO₆ 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 MnSb₂O₆. Ab initio DFT calculations demonstrate that the strongest exchange coupling occurs between planes along diagonals. All exchange parameters are antiferromagnetic and reveal moderate frustration.

A new tilt and an old twist on the nickel arsenide structure-type: synthesis and characterisation of the quaternary transition-metal cyanamides A2MnSn2(NCN)6 (A = Li and Na)

In this work, we describe the synthesis and structure of the quaternary transition-metal cyanamides Na2MnSn2(NCN)6 and Li2MnSn2(NCN)6. These phases crystallise isotypically in layered structures, with P3[combining macron]1m symmetry, that comprise hexagonal close-packed arrays of NCN2- anions with metal cations in 5/6 of the octahedral holes, thereby reflecting low-symmetry modifications of the hierarchical [NiAs]-type MNCN structure. The distinct coordination requirements of the metal cations template an ordered decoration across the octahedral sites with corundum-like [Sn2(NCN)3]2+ layers alternating with [A2Mn(NCN)3]2- layers which resemble a portion of the Li2Zr(NCN)3 structure. This motif is also mirrored in the form of the NCN2- anions which adopt N-C[triple bond, length as m-dash]N2- cyanamide shapes with clear single- and triple-bond character. Distortion-mode analysis reveals the importance of K1 octahedral twist and K2 cyanamide tilt displacements in stabilising these phases, the latter of which is only accessible because of the extended nature of the NCN2- anion. These are the first examples of non-binary transition-metal cyanamides to be discovered and this study highlights how the additional flexibility of the NCN2- anion affords a novel structure-type not observed in oxide chemistry.

New series of honeycomb ordered oxides, Na3M2SbO6 (M(ii) = Mn, Fe, (Mn, Fe), (Mn, Co)): synthesis, structure and magnetic properties

New members, Na₃M₂SbO₆ (M = Mn, Fe) belonging to the honeycomb family of oxides have been identified through chemical tuning of the oxidation states. The stabilization of Mn²⁺ (d⁵) and Fe²⁺ (d⁶) cations in the honeycomb geometry lead to various magnetic interactions.

Trigonal layered rosiaite-related antiferromagnet MnSnTeO6: ion-exchange preparation, structure and magnetic properties

Ion-exchange treatment of Na2SnTeO6 in molten salt mixtures resulted in rosiaite (PbSb2O6)-related MnSnTeO6. Its crystal structure was refined by the Rietveld method. Of the three possible models of Sn/Te distribution, the disordered model (P3[combining macron]1m, a = 5.23093(11) Å, c = 4.62430(16) Å) was preferred based on bond distances. However, it is supposed that each individual (SnTeO6)2- layer retains complete ordering of the precursor and the apparent disorder is only due to stacking faults. Magnetic studies have shown that MnSnTeO6 orders antiferromagnetically at Neél temperature TN = 9.8 K. The effective magnetic moment reasonably agrees with theoretical estimations assuming high-spin configuration of Mn2+ (S = 5/2). Electron spin resonance reveals spin dynamics in accordance with antiferromagnetic ordering. Moreover, critical broadening of ESR linewidth indicates the low-dimensional type of exchange interactions. Based on the temperature and field-dependent magnetization studies, the magnetic phase diagram of the new compound was constructed.