We studied the structural properties of an orbital-spin-coupled spinel oxide, ${\mathrm{MnV}}_2{\mathrm{O}}_4$, mainly by single-crystal x-ray diffraction measurement. It was found that a structural phase transition from cubic to tetragonal and ferrimagnetic ordering occur at the same temperature ($T_s,T_N=57\mathrm{K}$). The structural phase transition was induced also by magnetic field above $T_s$. In addition, magnetic-field-induced alignment of tetragonal domains results in large magnetostriction below $T_s$. We also found that the structural phase transition is caused by the antiferro-type ordering of the $V$ $t_{2g}$ orbitals.

• Received 11 December 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.127203