New Phase of MnSb sub(2)O sub(6) Prepared by Ion Exchange: Structural, Magnetic, and Thermodynamic Properties

A new layered trigonal (P31m) form of MnSb sub(2)O sub(6), isostructural with MSb sub(2)O sub(6) (M = Cd, Ca, Sr, Pb, and Ba) and MAs sub(2)O sub(6) (M = Mn, Co, Ni, and Pd), was prepared by ion-exchange reaction between ilmenite-type NaSbO sub(3) and MnSO sub(4)-KCl-KBr melt at 470 [degrees]C. It is characterized by Rietveld analysis of the X-ray diffraction pattern, electron microprobe analysis, magnetic susceptibility, specific heat, and ESR measurements as well as by density functional theory calculations. MnSb sub(2)O sub(6) is very similar to MnAs sub(2)O sub(6) in the temperature dependence of their magnetic susceptibility and spin exchange interactions. The magnetic susceptibility and specific heat data show that MnSb sub(2)O sub(6) undergoes a long-range antiferromagnetic order with Neel temperature T sub(N) = 8.5(5) K. In addition, a weak ferromagnetic component appears below T sub(1) = 41.5(5) K. DFT+U implies that the main spin exchange interactions are antiferromagnetic, thereby forming spin-frustrated triangles. The long-range ordered magnetic structure of MnSb sub(2)O sub(6) is predicted to be incommensurate as found for MnAs sub(2)O sub(6). On heating, the new phase transforms to the stable P321 form via its intermediate disordered variant.