The development of multifunctional nanomaterials through environmentally benign synthesis routes remains a key challenge for biomedical applications, particularly in photothermal therapy and diagnostic imaging. In this work, Fe3O4@Au core–shell nanoparticles (Fe3O4@Au NCS) were synthesized via a green approach using Zingiber purpureum Roscoe rhizome extract (ZPR extract) as a natural reducing and stabilizing agent. Structural and chemical characterization using XRD and FTIR confirmed the coexistence of spinel Fe3O4 and face-centered cubic Au phases, along with phytochemical surface capping derived from the plant extract. TEM and SAED analyses revealed a well-defined core–shell morphology with intimate interfacial contact between Fe3O4 and Au. Magnetic measurements showed a reduction in saturation magnetization due to the presence of the nonmagnetic Au shell, while maintaining superparamagnetic-like behavior at room temperature. Under 980 nm laser irradiation (2–3 W/cm2), the Fe3O4@Au NCS exhibited an efficient photothermal response, achieving temperature increases ranging from 5 to 28 °C. These findings demonstrate that ZPR-mediated Fe3O4@Au NCS combine magnetic responsiveness and strong photothermal conversion within a single hybrid system, highlighting their potential as multifunctional agents for diagnostic imaging and photothermal cancer therapy. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2026.