Structural, magnetic, and dielectric studies of cubically ordered Sr${}_2$FeMnO${}_6$

In this study, we determined the atomic composition, microstructure, crystallography, magnetisation, thermal, and dielectric properties of a double perovskite Sr${}_2$FeMnO${}_6$ system synthesised using sol-gel and sintering methods. X-ray fluorescence confirms the atomic composition of the Sr${}_2$FeMnO${}_6$ system. Scanning electron microscopy and energy-dispersive X-ray analyses reveal nonuniform grain distribution, with an average grain size of approximately 2.12 µm. X-ray diffraction analysis confirms that the Sr${}_2$FeMnO${}_6$ crystallised as a double-perovskite structure with a cubic cell belonging to Fm3m (225) symmetry. X-ray photoelectron spectroscopy (XPS) spectra of Fe 2p and Mn 2p core levels confirm the mixed chemical ionic states of Fe (Fe${}^{3+}$ and Fe${}^{4+}$) and Mn (Mn${}^{3+}$ and Mn${}^{4+}$) in the Sr${}_2$FeMnO${}_6$ system. O 1 s XPS spectra reveal oxygen existing in the form of lattice oxygen and oxygen vacancies while Sr is presented as Sr${}^{2+}$. The Raman phonon modes confirm phase purity and Fe/MnO${}_6$ octahedral vibration of the system. The Sr${}_2$FeMnO${}_6$ system exhibits a ferrimagnetic nature with a remnant magnetisation value of approximately 0.11 µB/f.u. Differential scanning calorimetry reveals a heat-flow peak temperature of 862.1 °C, which possibly corresponds to a magnetic transition temperature. Finally, the temperature-dependent dielectric constant confirms the existence of a ferroelectric-paraelectric transition at 528 K. Dielectric relaxation behaviour, with an activation energy of approximately 1.93 eV, is observed and is caused by the thermal motion of double ionised oxygen vacancies.