High-temperature magneto-structural coupling in the Sr(Fe1/2Nb1/2)O3 system

Abstract

We report the high-temperature phase transitions in the technologically important lead (Pb-) free B-site disordered Sr(Fe1/2Nb1/2)O3 (SFN) perovskite using dc magnetization and x-ray/neutron diffraction measurements. Our dc magnetization M (T) study reveals two magnetic transitions around 620 K and 708 K for the first time. The magnetic transition occurring around 620 K is linked with the structural phase transition, as confirmed by the temperature-dependent x-ray diffraction studies. Interestingly, the octahedral tilt angle (φ) and the integrated intensity of the superlattice reflection (ISL) decrease continuously with increasing temperature and vanishes across the structural phase transition. We have modeled the temperature variation of both φ and ISL using the power law type functional dependence which suggests the tricritical nature of the phase transition. Another transition occurring around 708 K in the M (T) plot is driven by oxygen vacancies. Neutron powder diffraction analysis of SFN at 295 K shows no sharp magnetic Bragg peaks, which are characteristic of long-range magnetic order. Instead, it reveals diffuse scattering, suggesting the presence of short-range magnetic ordering.