Structural, Magnetic, and Magnetothermal Properties of Co100−xNix Nanoparticles for Self-Controlled Hyperthermia

In this study, the structural and magnetic properties of a series of functionalized Co100−xNix (x = 20, 30, 40, 50, 60, 80, 85) nanoparticles (NPs) were analyzed with the objective of attaining a high specific absorption rate (SAR). The magnetic nanoparticles (MNPs) obtained by ball milling at 1425 rpm lie in the range of 03–29 nm and are studied as potential candidates for magnetic fluid hyperthermia. Magnetic measurements show that all samples possess soft ferromagnetic properties with the reduction in the Curie temperature (TC) by Ni substitution in Co100−xNix alloys and by ball milling. The specific absorption rate (SAR) and specific loss power (SLP) obtained from magnetothermal measurements for powder and fluid samples lie in the range 4.4–83 W/g and 19–382 W/g, respectively, showing strong dependence on structural and magnetic properties. The SAR/SLP values as a function of the applied field at 425 kHz display a square dependence on the applied magnetic field below 165 Oe, which is expected for single domain ferromagnetic nanoparticles, but deviate from this at higher values of the applied field. We also obtained the effective anisotropy constant Keff for ball-milled nanoparticles at 1425 rpm for 200, 300, and 500 min. within the framework of linear response theory, showing strong dependence on average crystallite size. Additionally, the toxicity of the prepared nanoparticles in the form of percentage hemolysis was controlled with oleic acid.