Annealing influence on the magnetic and thermal stability of FeNi3 nanoparticles for magnetic hyperthermia applications

Metallic magnetic nanoparticles having excellent magnetic properties are potential candidate for biomedical applications like magnetic hyperthermia and drug delivery, however their long-term stability remains a critical challenge, limiting their utility for such applications. Monodisperse spherical FeNi3 permalloy nanoparticles (NPs) were synthesized by surfactant free polyol method and their magnetic and thermal stability was tested for magnetic hyperthermia. The synthesized NPs possessed FCC phase and spherical morphology with average diameter of similar to 155 nm. The structural ordering and morphology were improved upon annealing treatment at 300 degrees C resulting in enhanced magnetic properties where the saturation magnetization increased from 54 emu/g to 78 emu/g. The magnetic properties were retained over a long period in ambient conditions. Further, the thermogravimetric measurements in ambient conditions established the thermal stability of the nanoparticles up to 350 degrees C. Transmission electron microscopy revealed a protective amorphous coating all over the NP surface, which shield them from corrosion in ambient conditions. These highly stable NPs showed excellent magnetic hyperthermia response in water as well as ethylene glycol medium. The specific absorption rate of the NPs was improved upon annealing from 268 W/g to 299 W/g in water. The long-term magnetic and thermal stability of these NPs and their excellent SAR values makes them a suitable candidate for magnetic hyperthermia-based cancer therapy.