Solvothermal synthesis, microstructure and magnetic properties of α-Fe2O3/ε-Fe2O3 hybrid superparticles.

α-Fe2O3/ε-Fe2O3 hybrid superparticles were successfully synthesized via a solvothermal method at 125 °C. Microstructural analyses revealed that the samples exhibited high crystallinity and were composed of a dual-phase system, with α-Fe2O3 and ε-Fe2O3 accounting for 97.37% and 2.63% respectively. The synthesized hybrid superparticles initially formed as nanoparticles, which subsequently self-assembled into ellipsoidal structures. Magnetic characterization indicated that the α-Fe2O3/ε-Fe2O3 hybrid superparticles exhibited a coercivity of 4.69 kOe at 300 K. At 4 K, both the coercivity and remanent magnetization exhibited a significant increase. At 380 K, the thermal excitation effect became more pronounced, and the hysteresis loop exhibited a special magnetization characteristic where domain wall displacement and magnetic moment rotation dominated at different stages. The temperature-dependent magnetization (M-T) curves measured under zero-field-cooled (ZFC) and field-cooled (FC) conditions revealed magnetic irreversibility. The derivative of the ZFC magnetization with respect to temperature (d(MZFC)/dT) identified a freezing temperature (Tf) of 116 K and a blocking temperature (TB) of 257 K. This study proposes a nucleation-aggregation-growth mechanism induced by coordination for the formation of α-Fe2O3/ε-Fe2O3 hybrid superparticles. The synthesized hybrid superparticles exhibit relatively high coercivity at room temperature and excellent stability, and their magnetic properties display a pronounced temperature dependence. These characteristics suggest promising potential for applications in magnetic recording media, magnetic sensors, and intelligent magnetic devices.