Asymmetry of electron and hole doping inYMnO3

We synthesized hexagonal ${\mathrm{YMnO}}_3$ doped with tetravalent Zr ions and studied the electronic and magnetic properties. Zr substitution creates a mixed ${\mathrm{Mn}}^{3+}-{\mathrm{Mn}}^{2+}$ system, instead of the conventional ${\mathrm{Mn}}^{3+}-{\mathrm{Mn}}^{4+}$ of colossal magnetoresistance manganites. The ${\mathrm{YMnO}}_3$ system displays a pronounced asymmetry for electron and hole doping. Hole doping results in a conducting state, whereas electron doping retains the insulating state. This asymmetry is a consequence of the crystal field splitting of the Mn ions in trigonal bipyramidal coordination.