ИСТИНА

We report on the magnetic properties of four new metastable trigonal layered MSb2O6 phases (M =Mn, Co, Ni, Cu), which have been prepared by the low-temperature ion-exchange reactions. Except CuSb2O6, all compounds under study demonstrate a long-range antiferromagnetic order at low temperatures with Neel temperatures ~8 K (Mn), ~11 K (Co) and ~15 K (Ni) respectively. In addition, the magnetization isotherms indicate a magnetic field induced spin-reorientation (spin-flop type) transition below TN at BSF ~ 0.8 T for MnSb2O6 and BSF ~ 8 T for CoSb2O6 respectively, implying two different spin-configurations in the ordered phases. It is interesting to note that the magnetic properties observed here for these novel compounds possessing the trigonal layered rosiaite-type structure are essentially different from those reported for their stable polymorphs MSb2O6 (M = Ni, Co, Cu) with tetragonal trirutile-type structure. Magnetic behavior of all trirutile-type compounds MSb2O6 (M = Ni, Co, Cu) is quite similar. A characteristic feature is the presence of a wide temperature range where all MSb2O6 with trirutile structure exhibit short-range antiferromagnetic order and the temperature dependence of the magnetic susceptibility (T) demonstrates clear low-dimensional broad maximum at Tmax followed by long-range antiferromagnetic order. Despite the nearly perfect 2D square M2+ sublattice the data were well described within the formalism of antiferromagnetic 1D spin chain. In contrast, new metastable MSb2O6 phases (M =Mn, Co, Ni, Cu) did not show any sign of low-dimensional behavior and the magnetic susceptibility nicely follows the Curie-Weiss law over the wide temperature range higher TN. The negative values of Curie-Weiss temperature indicate predominance of the antiferromagnetic interactions and moderate frustration for the 2D triangular M2+ magnetic sublattice. The effective magnetic moments calculated from the obtained Curie constants are in excellent agreement with theoretical estimations using the average effective g-factor, which was directly measured by means of electron spin resonance (ESR).