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

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.