Phase transformations and magnetic properties of non-stoichiometric strontium ferromolybdate cations

Abstract

This study investigates the phase transformation dynamics during the synthesis of non-stoichiometric strontium ferromolybdate (Sr₂Fe₁.₂Mo₀.₈O₆₋δ, SFMO) via solid-state reaction from SrCO₃, Fe₂O₃, and MoO₃. Intermediate phases SrFeO₃ and SrMoO₄ form sequentially between 500–850 K and hinder complete SFMO crystallization due to kinetic limitations at high temperatures (≥1270 K). To overcome this, combined synthesis modes involving controlled heating rates and intermediate grinding were developed, enabling the production of single phase SFMO with 89% Fe/Mo superstructural ordering. Magnetic characterization revealed that reduced cation ordering increases antiferromagnetic clustering, suppressing long-range ferrimagnetic order and lowering magnetization in field-cooling measurements. Zero field-cooling data confirmed superparamagnetic behavior, indicating magnetic inhomogeneity with coexisting superparamagnetic nanoparticles and ferrimagnetic grains. The results demonstrate that precise control of synthesis conditions is essential to minimize kinetic barriers, suppress defect formation, and achieve reproducible magnetic properties in SFMO, a promising candidate for spintronic applications.