Novel Spin-Orbital Phases Induced by Orbital Dilution

We demonstrate that magnetic 3d impurities with S = 3/2 spins and no orbital degree of freedom induce changes of spin-orbital order in a 4d4 Mott insulator with S = 1 spins. Impurities act either as spin defects which decouple from the surrounding ions, or trigger orbital polarons along 3d- 4d bonds. The 4d- 4d superexchange in the host Jhost competes with 3d- 4d superexchange Jimp--it depends on which orbital is doubly occupied. The spin-orbital order within the host is totally modified at doping x = 1/4. Our findings provide new perspective for future theoretical and experimental studies of doped transition-metal oxides