Particle size and shape effects on the magnetic behaviour of samarium hexacyanoferrate Prussian blue analogue

Abstract

We report the controlled synthesis of samarium–iron Prussian blue analogues (SmFe PBAs) with novel morphologies, achieved through a systematic reverse micelle strategy using the non-ionic surfactant Triton X-100. By varying key experimental parameters—such as the water-to-surfactant molar ratio (ω₀), the concentration of TX-100, and the volumetric ratio of cyclohexane to surfactant—we obtained a diverse range of particle shapes, including unprecedented daisy-like architectures with 4, 5, and 6 petals. These morphologies emerge within a narrow compositional window, implicating the formation of reverse bilayer vesicles as transient templates during nucleation and growth. Detailed morphological and structural characterization (TEM, SEM, XPS, PXRD, IR spectroscopy) revealed size-tunable particles ranging from 250 nm to 7 μm, while silica coating was achieved via a two-step sol–gel route enabling further miniaturization. Magnetic measurements highlight a strong size- and shape-dependent variation in coercive field (H_c), reaching up to 3320 Oe in submicron particles—among the highest reported for SmFe PBAs—attributed primarily to enhanced shape anisotropy. Our findings provide new insights into PBAs’ morphology–property relationships and open pathways toward engineering anisotropic magnetic nanomaterials through soft templating in reverse micellar systems.