We have studied relationship between local lattice disorder, Ru 4d spin-orbit interaction, and global spin/orbital orders of Ca 2-xSrxRuO4 in the Sr- and Ca-rich regions of its phase diagram by using unrestricted Hartree-Fock calculation on a 8 × 8 RuO4 lattice model. The calculations show that the local elongation of RuO 6 octahedron in an antiferromagnetic insulator Ca2RuO 4 induces local orbital change with making the Mott gap narrower. On the other hand, local compression of RuO6 octahedron in a paramagnetic metal Sr2RuO4 induces global antiferromagnetic or ferromagnetic states. This result is consistent with a recent systematic μSR study by Carlo et al. which has revealed the static antiferromagnetic order at low temperature in the Sr-rich region.
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