Mössbauer study on the CMR double perovskite AFe_0.5Mo_0.5O₃ with A=(Ba,Sr) or (Sr,Ca): Chemical pressure effect

Summary

The double perovskites, AFe_0.5Mo_0.5O₃with A=(Ba,Sr) or (Sr,Ca), were prepared by a sol-gel method, and the substitution effect at site A was studied by Mössbauer spectrometry. In the Mössbauer spectra of the double perovskite (Ba, Sr)Fe_0.5Mo_0.5O₃, the isomer shifts decreased fromδ=0.72 mm/s to δ=0.4 mm/s and the internal magnetic fields increased with the increase of the Sr content. The Ba-rich samples were shown to contain superparamagnetic components under the same preparation conditions. Better crystallinity and larger hyperfine fields were obtained when 5% of the Sr-content of SrFe_0.5Mo_0.5O₃was substituted by Ca as compared with substitution by Ba. Phonon density of states (DOS) of SrFe_0.5Mo_0.5O₃substituted with Ca or Ba were obtained by nuclear inelastic scattering. The peaks of phonon DOS were shifted, depending on chemical compression/expansion of the lattice. The chemical pressure effect could be observed in the Mössbauer spectra and the phonon DOS spectra.