Evidence for valence fluctuation of Fe in Sr2FeMoO6−w double perovskite

Abstract

In this letter evidence for the formation of a valence-fluctuation state of iron, formally denoted as ${\mathrm{Fe}}^{\mathrm{2.5+}},$ is presented. The system under study is the ${\mathrm{Sr}}_{\mathrm{2}}{\mathrm{FeMoO}}_{\text{6−w}}$ double perovskite, known for exhibiting a very large magnetoresistance. Samples of ${\mathrm{Sr}}_{\mathrm{2}}{\mathrm{FeMoO}}_{\text{6−w}}$ were synthesized by means of an encapsulation technique utilizing an Fe getter technique and characterized by ${}^{\mathrm{57}}\mathrm{Fe}$ Mössbauer spectroscopy. From 5 K to room temperature the Mössbauer spectrum is dominated by a component with hyperfine parameter values between those expected for high-spin ${\mathrm{Fe}}^{\mathrm{3+}}$ and high-spin ${\mathrm{Fe}}^{\mathrm{2+}}.$