High-Frequency Specific Absorption Rate of CoxFe1−xFe2O4 Ferrite Nanoparticles for Hipertermia Applications

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Abstract
The heating processes in ferrofluids in ac magnetic field depend on chemical composition, dimension, shape, magnetic properties of the nonoparticles, and rheological characteristics of the dispersing medium. By controlling these parameters, a maximum energy can be transferred to the medium. This paper was focused on determining the specific absorption rate (SAR) of a series of nanoparticles (NPs), with ferromagnetic properties at room temperature, dispersed in water to prove their possible use in medical applications. CoxFe 3-x O 4 (with x = 0.2-1 in steps of 0.2) magnetic fluids were synthesized by the coprecipitation method and subjected to an ac magnetic field with different amplitudes and distinct frequencies. X-ray difractometry and transmission electron microscopy were used to characterize the phase and microstructure of NPs. Vibrating sample magnetometer measurements denoted a ferrimagnetic behavior of the particles at room temperature and expected superparamegnetic behavior for ferrofluids. The values of SAR obtained using a calorimetric method, at fixed frequency, increased with strength of applied field and Co content being higher at low frequencies. The results are explained in terms of relaxation times, and the experimental data were compared with theoretical predictions.

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