We studied the magnetic and structural properties of spinel ${\mathrm{MnV}}_2{\mathrm{O}}_4$, which has $S=5/2$ spin with no orbital degrees of freedom on the ${\mathrm{Mn}}^{2+}$ site and $S=1$ spin and three orbital degrees of freedom on the ${\mathrm{V}}^{3+}$ site. We found that the ferrimagnetic ordering at $T_{\mathrm{N}}=56.5\mathrm{K}$ and the structural phase transition at $T_{\mathrm{s}}=53.5\mathrm{K}$ are closely correlated in this compound and found a switching of crystal structure between cubic and tetragonal phases by the magnetic field. This phenomenon can be explained by the coupling between orbital and spin degrees of freedom in the $t_{2\mathrm{g}}$ states of the V site.

• Received 26 April 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.197202