Magnetic harmony: investigation of interfacial exchange-coupling induced AFM phase transition in Fe ₃ S ₄ /Fe ₃ O ₄ nanocomposites

Magnetic phase transitions emerging from interfacial exchange coupling have been scarcely reported in magnetic nano composites, underscoring the significance of their observation. In this study, Fe₃S₄/Fe₃O₄composites were synthesized via a solvothermal method using magnetite (Fe₃O₄) seeds of two different sizes (∼80 nm and ∼9 nm) to investigate the influence of seed size on structural and magnetic properties. Rietveld-refined x-ray diffraction (XRD) confirmed the coexistence of Fe₃S₄and Fe₃O₄phases in the composites. Isothermal magnetization measurements at room temperature revealed an increase in saturation magnetization with higher Fe₃O₄content. Notably, temperature-dependent magnetization of composites with ∼80 nm seeds exhibited a distinct transition at 114 K, attributed to antiferromagnetic (AFM) interfacial exchange coupling. Temperature-dependent XRD studies of the composite revealed no structural phase transition at low temperatures; however, the evolution of lattice parameters and crystal planes in the transition region indicates structural distortions and atomic displacements, suggesting the presence of spin-lattice coupling. This transition is distinctly identified as interfacial AFM exchange coupling, excluding possibilities such as compensation point, Morin transition, spin-flop transition, or Verwey transition. However, this transition was absent in the composite synthesized using ∼9 nm Fe₃O₄seeds suggesting a reduced interfacial coupling. These findings highlight the crucial role of Fe₃O₄seed size in governing the interfacial magnetic interactions in Fe₃S₄/Fe₃O₄nanocomposites and demonstrate their potential for applications such as spintronics, magnetic recording, sensors, and electromagnetic wave absorption.