From antiferromagnetism to high-T c weak ferromagnetism manipulated by atomic rearrangement in Ba 3 NiOs 2 O 9

摘要: Polycrystalline samples of $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ were synthesized at ambient pressure (AP) and high (HP) conditions, respectively. Both are electrically semiconducting. The AP crystallizes in the $6H$ perovskite structure with space group $P{6}_{3}/mmc$, consisting face-sharing $\mathrm{O}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ dimer units corner-sharing $\mathrm{Ni}{\mathrm{O}}_{6}$ octahedra. Magnetic measurements indicated that is antiferromagnetically ordered below 130 K. HP too, but octahedral sites appear to be occupied by both $\mathrm{N}{\mathrm{i}}^{2+}$ $\mathrm{O}{\mathrm{s}}^{5+}$ ions, whereas site exclusively $\mathrm{O}{\mathrm{s}}^{5+}$. undergoes a high-temperature ($\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}400\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) weak ferromagnetic transition, which much different from antiferromagnetism phase. long-range magnetic order was confirmed neutron powder diffraction. X-ray circular dichroism analysis supported coupling between Os Ni moments leads spin arrangement, where mainly arise ions.