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Spinel oxide MgV2O4 is a S=1 pyrochlore antiferromagnet, where a long range
magnetic ordering is suppressed by the presence of strong geometrical frustration. On cooling, an anti-ferromagnetic ordering emerges marginally at TN=40 K, triggered by a structural transition from cubic to tetragonal at Ts=62 K. In this study, detailed structural analysis of MgV2O4 was conducted, using high resolution synchrotron x-ray diffraction and convergent electron beam diffraction (CBED). We revealed that the tetragonal phase below TS has the symmetry of I41/a and that the distortion pattern of VO6 octahedra is consistent with the A-type antiferro-orbital ordering with alternating stack of layers with yz/xy orbital chains and zx/xy orbital chains along the tetragonal c-axis. This implies that an anisotropic coupling of V moments produced by the orbital ordering below TS brings about primarily the anti-ferromagnetic ordering. |
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