Magnetic transitions in double perovskiteSr2FeRe1−xSbxO6(0⩽x⩽0.9)

Abstract

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 ${\mathrm{Sr}}_{2}{\mathrm{FeRe}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}{\mathrm{O}}_{6}$ $(0<x<0.9)$ 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 $^{121}\mathrm{Sb}$ M\"ossbauer 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, $^{57}\mathrm{Fe}$ M\"ossbauer 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 $\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Re}(\mathrm{Sb})\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}$ along the crystallographic axis of the perovskite unit cell and destroys the itinerant magnetism of the parent compound.