Transport, magnetic, and structural properties of spinel MnTi2 O4 and the effect of V doping

We studied the transport, magnetic, and structural properties of spinel MnTi2 O4 and V-doped samples, MnTi2-x Vx O4, 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 MnTi2 O4 at 180 K, which is presumably dominated by the ordering of t2g 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 MnTi2-x Vx O4 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, MnV2 O4, the electrical resistivity increases again and another type of structural phase transition occurs at 53 K. Large magnetostriction was observed in MnV2 O4, the only compound in this series to have both a ferrimagnetic state and tetragonal lattice distortion.