Dimension reduction due to the orbital ordering has recently been proposed to explain the exotic charge, magnetic and structural transitions in some three-dimensional (3D) transitional metal oxides. We present optical measurement on a spinel compound MgTi2O4 which undergoes a sharp metalinsulator transition at 240 K, and show that the spectral change across the transition can be well understood from the proposed picture of 1D Peierls transition driven by the ordering of dyz and dzx orbitals. We further elaborate that the orbital-driven instability picture applies also very well to the optical data of another spinel CuIr2S4 reported earlier.

Schematic illustration of strain-mediated magnetization precessional switching and a domain wall injection mechanism in a nano-magnet with in-plane shape anisotropy.

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