High-Pressure Synthesis and Ferrimagnetism of Ni 3 TeO 6 -Type Mn 2 ScMO 6 (M = Nb, Ta).

The corundum-related oxides Mn ₂ ScNbO ₆ and Mn ₂ ScTaO ₆ were synthesized at high pressure and high temperature (6 GPa and 1475 K). Analysis of the synchrotron powder X-ray diffraction shows that Mn ₂ ScNbO ₆ and Mn ₂ ScTaO ₆ crystallize in Ni ₃ TeO ₆ -type noncentrosymmetric crystal structures with space group R 3. The asymmetric crystal structure was confirmed by second harmonic generation measurement. X-ray absorption near-edge spectroscopies indicate formal valence states of Mn ²⁺ ₂ Sc ³⁺ Nb ⁵⁺ O ₆ and Mn ²⁺ ₂ Sc ³⁺ Ta ⁵⁺ O ₆ , also supported by the calculated bond valence sums. Both samples are electrically insulating. Magnetic measurements indicate that Mn ₂ ScNbO ₆ and Mn ₂ ScTaO ₆ order ferrimagnetically at 53 and 50 K, respectively, and Mn ₂ ScTaO ₆ is found to have a field-induced magnetic transition.