Magnetic Softness and Hyperthermia Efficiency of Fe3O4-Au Nanoparticles with Silica Shell

Magnetite (Fe 3 O 4 ) nanoparticles (NPs) are promising agents for magnetic hyperthermia (MH) due to their high magnetization, low coercivity, and biocompatibility. Here, Fe 3 O 4 NPs were synthesized via co-precipitation, functionalized with gold (Au) for localized surface plasmon resonance (LSPR), and coated with silica (SiO 2 ) for biocompatibility and tunable plasmonic enhancement. Transmission electron microscopy (TEM) confirmed the presence of Fe 3 O 4 core with an average size of 12.5 ± 2.1 nm, Au surface decoration, and uniform SiO 2 shells of 3.7 ± 0.6 nm thickness. Magnetic measurements revealed soft ferrimagnetic behavior, with a progressive decrease in saturation magnetization upon addition of diamagnetic layers. The normalized magnetization curves indicated a slower magnetic saturation after Au integration, suggesting interfacial magnetic pinning effects. Magnetic hyperthermia tests at 310 kHz and 400–800 Oe yielded high specific absorption rate (SAR) values for Fe 3 O 4 NPs (up to 379.16 W/g) and ∼50% retention post-coating, with intrinsic loss power (ILP) values comparable to some commercial Fe 3 O 4 systems. These results highlight the potential of hybrid Fe 3 O 4 -Au@SiO 2 nanoparticles as multifunctional, biocompatible platforms.