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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 modelin a three-dimensional simple-cubic lattice are analyzed by the Monte-Carlosimulation and the cluster expansion method. In the $e g$ orbital model withoutspin degree of freedom, reduction of the orbital ordering temperature due todilution is steeper than that in the dilute magnet. This is attributed to amodification of the orbital wave-function around vacant sites. In thespin-orbital coupled model, it is found that magnetic structure is changed fromthe A-type antiferromagnetic order into the ferromagnetic one. Orbitaldependent exchange interaction and a sign change of this interaction aroundvacant sites bring about this novel phenomena. Present results explain therecent experiments in transition-metal compounds with orbital dilution.



Author: Takayoshi Tanaka, Sumio Ishihara

Source: https://arxiv.org/



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