Transport, magnetic, and structural properties of spinelMnTi2O4and the effect of V doping

Abstract

We studied the transport, magnetic, and structural properties of spinel ${\mathrm{MnTi}}_{2}{\mathrm{O}}_{4}$ and V-doped samples, ${\mathrm{MnTi}}_{2\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{O}}_{4}$, to clarify the relation between charge, spin, and orbital degrees of freedom of $3d$ electrons in this series of compounds. A structural phase transition occurs in ${\mathrm{MnTi}}_{2}{\mathrm{O}}_{4}$ at $180\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which is presumably dominated by the ordering of ${t}_{2\mathrm{g}}$ orbitals, but it can be easily suppressed by the V doping to the Ti site. Associated with this suppression of the structural anomaly, a ferrimagnetic and electrically conducting state appears in ${\mathrm{MnTi}}_{2\ensuremath{-}x}{\mathrm{V}}_{x}{\mathrm{O}}_{4}$ with finite values of $x$. Fairly large magnetoresistance was observed in this state, whose sign changes from positive to negative with an increase in the V concentration $x$. With approaching the other end of this series, ${\mathrm{MnV}}_{2}{\mathrm{O}}_{4}$, the electrical resistivity increases again and another type of structural phase transition occurs at $53\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Large magnetostriction was observed in ${\mathrm{MnV}}_{2}{\mathrm{O}}_{4}$, the only compound in this series to have both a ferrimagnetic state and tetragonal lattice distortion.