The double perovskites ${\mathrm{Sr}}_2\mathrm{Fe}M{\mathrm{O}}_6$ $(M=\mathrm{Re},\mathrm{Mo})$ belong to the important class of half-metallic magnetic materials. In this study we explore the effect of replacing the electronic $5d$ buffer element Re with variable valency by the main group element Sb with fixed valency. X-ray diffraction reveals ${\mathrm{Sr}}_2{\mathrm{FeRe}}_{1-x}{\mathrm{Sb}}_x{\mathrm{O}}_6$ $(0<x<0.9)$ to crystallize without antisite disorder in the tetragonally distorted perovskite structure (space group $I4∕mmm$). The ferrimagnetic behavior of the parent compound ${\mathrm{Sr}}_2{\mathrm{FeReO}}_6$ changes to antiferromagnetic upon Sb substitution as was determined by magnetic susceptibility measurements. Samples up to a doping level of 0.3 are ferrimagnetic, while Sb contents higher than 0.6 result in an overall antiferromagnetic behavior. ${}^{57}\mathrm{Fe}$ and ${}^{121}\mathrm{Sb}$ Mössbauer spectroscopy specifies the valence state of Sb to be $+5$ within the whole range of substitution whereas the Fe valence state changes from $+2.7$ for the parent compound to $+2.9$ for ${\mathrm{Sr}}_2{\mathrm{FeRe}}_{0.1}{\mathrm{Sb}}_{0.9}{\mathrm{O}}_6$. Accordingly, Fe adopts the role of an electronic buffer element from Re upon heavy Sb doping. Additionally, ${}^{57}\mathrm{Fe}$ Mössbauer results show a coexistence of ferri- and antiferromagnetic clusters within the same perovskite-type crystal structure in the Sb substitution range $0.3<x<0.8$, whereas ${\mathrm{Sr}}_2{\mathrm{FeReO}}_6$ and ${\mathrm{Sr}}_2{\mathrm{FeRe}}_{0.9}{\mathrm{Sb}}_{0.1}{\mathrm{O}}_6$ are “purely” ferrimagnetic and ${\mathrm{Sr}}_2{\mathrm{FeRe}}_{0.1}{\mathrm{Sb}}_{0.9}{\mathrm{O}}_6$ contains antiferromagnetically ordered Fe sites only. Consequently, a replacement of the Re atoms by a nonmagnetic main group element such as Sb blocks the superexchange pathways $\text{−}\mathrm{Fe}\text{−}\mathrm{O}\text{−}\mathrm{Re}\left(\mathrm{Sb}\right)\text{−}\mathrm{O}\text{−}\mathrm{Fe}\text{−}$ along the crystallographic axis of the perovskite unit cell and destroys the itinerant magnetism of the parent compound.

• Received 25 August 2005

DOI:https://doi.org/10.1103/PhysRevB.73.144414