Novel Spin-Orbital Phases Induced by Orbital Dilution

TL;DR

This paper explores how magnetic 3d impurities with no orbital degree of freedom alter spin-orbital order in a 4d Mott insulator, revealing impurity-induced phases and complex interactions.

Contribution

It introduces a novel understanding of impurity effects on spin-orbital order, including orbital polarons and the competition between different superexchange interactions.

Findings

Impurities can decouple spins or induce orbital polarons.

Spin-orbital order is fully modified at 25% doping.

Impurity effects depend on orbital occupancy and exchange interactions.

Abstract

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 $4d^4$ 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 $J_{\rm host}$ competes with $3d$-$4d$ superexchange $J_{\rm imp}$ --- 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.