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Abstract:
Polycrystalline samples of Ba3NiOs2O9 were synthesized at ambient pressure (AP) and high pressure (HP) conditions, respectively. Both samples are electrically semiconducting. The AP Ba3NiOs2O9 crystallizes in the 6 H perovskite structure with space group P6(3)/mmc , consisting of face-sharing Os2O9 dimer units and corner-sharing NiO6 octahedra. Magnetic measurements indicated that AP Ba3NiOs2O9 is antiferromagnetically ordered below 130 K. HP Ba3NiOs2O9 crystallizes in the 6H perovskite structure too, but the face-sharing octahedral sites appear to be occupied by both Ni2+ and Os5+ ions, whereas the corner-sharing site is occupied exclusively by Os5+ . HP Ba3NiOs2O9 undergoes a high-temperature (approximate to 400 K) weak ferromagnetic transition, which is much different from the antiferromagnetism of the AP phase. The long-range magnetic order of HP Ba3NiOs2O9 was confirmed by neutron powder diffraction. X-ray magnetic circular dichroism analysis supported ferromagnetic coupling between Os and Ni moments which leads to a spin arrangement, where the ferromagnetic moments mainly arise from Ni2+ ions.
