Wide-Range Tuning of the Mo Oxidation State in La1-xSrxFe2/3Mo1/3O3 Perovskites.

La_{1- x}Sr _xFe_2/3Mo_1/3O₃ (0 ≤ x ≤ 1) perovskites allow exceptionally wide tuning of the Mo oxidation state from +3 ( x = 0) to +6 ( x = 1) with the Fe^III oxidation state virtually unchanged. The end members of this series show antiferromagnetic ordering in LaFe_2/3Mo_1/3O₃ at T_N = 520 K and ferrimagnetic ordering in SrFe_2/3Mo_1/3O₃ at T_C = 420 K. The crucial role of electron correlations in the Mo 4d shell suggests that LaFe_2/3Mo_1/3O₃ with a half-filled band is a Mott insulator, whereas SrFe_2/3Mo_1/3O₃ is a band insulator. In both cases, the magnetic structure is dictated by antiferromagnetic superexchange between localized magnetic moments. At intermediate compositions, an interplay of antiferromagnetic-superexchange and double-exchange interactions results in nonmonotonous variations of both the magnetic-ordering temperature and saturation magnetization. [ABSTRACT FROM AUTHOR]