NMR evidence for selective enhancement of Mo magnetic moment by electron doping inSr2−xLaxFeMoO6

Abstract

${}^{95,97}\mathrm{Mo}$ NMR experiments have been performed on a series of ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ and electron-doped ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{FeMoO}}_{6}$ ceramics. A detailed analysis of the NMR spectra from pristine ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ conclusively shows that the Mo hyperfine field is mainly due to atomic Mo magnetic moments. No contribution of transferred hyperfine field has been observed, confirming the absence of s electrons in the conduction band. Upon La doping, the NMR frequency (hyperfine field) gradually increases, proving that the concentration of spin-polarized electrons at a Mo ion is enhanced by the La substitution. A simple linear correlation between a magnetic moment at Mo sites and the Curie temperature of the system has been found. Implications for understanding the electronic structure and the ferromagnetic coupling in these systems are underlined.