Dilution effect in correlated electron system with orbital degeneracy

TL;DR

This paper investigates how dilution affects orbital and magnetic orderings in correlated electron systems, revealing that dilution suppresses orbital order more steeply than in magnets and induces magnetic phase changes.

Contribution

The study introduces a theoretical analysis of dilution effects in orbital ordered systems using Monte-Carlo and cluster expansion methods, highlighting novel magnetic and orbital phenomena.

Findings

Orbital ordering temperature decreases more steeply than in dilute magnets.

Dilution induces a transition from A-type antiferromagnetic to ferromagnetic order.

Orbital-dependent exchange interactions change sign around vacant sites.

Abstract

Theory of dilution effect in orbital ordered system is presented. The $e_g$ orbital model without spin degree of freedom and the spin-orbital coupled model in a three-dimensional simple-cubic lattice are analyzed by the Monte-Carlo simulation and the cluster expansion method. In the $e_g$ orbital model without spin degree of freedom, reduction of the orbital ordering temperature due to dilution is steeper than that in the dilute magnet. This is attributed to a modification of the orbital wave-function around vacant sites. In the spin-orbital coupled model, it is found that magnetic structure is changed from the A-type antiferromagnetic order into the ferromagnetic one. Orbital dependent exchange interaction and a sign change of this interaction around vacant sites bring about this novel phenomena. Present results explain the recent experiments in transition-metal compounds with orbital dilution.