Unusual high-spin Fe5+ - Ni3+ state and strong ferromagnetism in the mixed perovskite SrFe0.5Ni0.5O3.

The charge-spin-orbital state plays a vital role in correlated oxides with mixed transition-metal elements, and it is often a matter of debate. Here, we address this issue for the newly synthesized unusual high-valence perovskite SrFe1-x Nix O3, using an analysis of crystal-field level diagrams, density functional calculations, and Monte Carlo simulations. We have identified the formal high-spin Fe5+ (t2g³, S = 3/2) and high-spin Ni3+ (t2g5e²g, S = 3/2) state for SrFe0.5 Ni0.5 O3, rather than the previously suggested high-spin Fe4+ (t2g³eg¹, S = 2) and low-spin Ni4+ (t2g6, S = 0) state. Moreover, our model and the present results well explain the observed small lattice variation of SrFe1-x Nix O3 (0 ≤ x ≤ 0.5) and the above room temperature ferromagnetic order in SrFe0.5 Ni0.5 O3 regardless of a Fe-Ni atomic order or disorder. [ABSTRACT FROM AUTHOR]