Magnetic hyperthermia is an important method for efficient cancer treatment. Magnetic hyperthermia with nanoparticles enables localised heating of the treated tissue, which makes this method attractive for a clinical use. The method is based on heat generated by magnetic losses due to the Néel and Brown relaxation. The heating efficiency is defined by Specific Absorption Rate (SAR), which is defined as the heating power generated per unit mass of the nanoparticles. For successful treatment we need to synthesize magnetic nanoparticles with the highest SAR at the given magnetic field. In this way, the concentration of nanoparticles needed for a sufficient local increase in temperature, is minimal.
In this research I analyse two different types of magnetic nanoparticles, cobalt-ferrite nanoparticles with a general chemical formula $({\rm Co}_x{\rm Fe}_{1-x})[{\rm Fe}_2]{\rm O}_4,$ where $x$ stands for cobalt fraction, and magnetite nanoparticles ${\rm Fe}_3{\rm O}_4.$ Nanoparticles are spherical with an average diameter of 15 nm, as seen from the microscopic measurements. Blocking temperature is below room temperature for all samples and varies between 152 K and 285 K for cobalt-ferrite nanoparticles, while it is lower for magnetite nanoparticles (around 35 K). Magnetization measurements exhibit no hysteresis at room temperature, and are modelled with two superparamagnetic contributions. This suggests a core-shell structure of nanoparticles. Measured SAR for cobalt-ferrite nanoparticles is $\sim$2 W/g, and $\sim$1 W/g for magnetite nanoparticles.
Measurements show that the samples are indeed superparamagnetic and that the influence of cobalt ions has significant impact on their magnetic properties. The presence of cobalt atoms in the structure increases SAR, most likely due to an increase in magnetic anisotropy. Further studies on the role of cobalt position in the spinel structure are needed to fully understand SAR of such nanoparticles.
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