Search

In this work, CoFe2O4/MnFe2O4 core/shell nanostructures were fabricated using the thermal decomposition method. CoFe2O4 (CFO) nanoparticles with an average size of about 10 nm were used as seeds for the growth of MnFe2O4 particles. X-ray diffraction (XRD) analysis results showed that the fabricated core/shell samples have a single-phase face-centered cubic spinel structure similar to the CoFe2O4 sample but with a larger crystal size. Moreover, transmission electron microscopy (TEM) observations showed that the size of nanoparticles of the core/shell samples increased by 1.0–3.5 nm with respect to that of the CoFe2O4 sample, indicating the formation of the MnFe2O4 shell layer. The magnetic measurement results showed that a thin MnFe2O4 shell existed in the core/shell samples resulting in an increased saturation magnetization (Ms) and a slight decrease in coercivity (Hc) compared to the CFO core sample. In contrast, a thicker shell layer resulted in decreased Ms and Hc values compared to the CFO core sample. The magnetic hysteresis curve measured at a low temperature and high magnetic field showed the difference between the reference mixed sample and the core/shell nanostructured sample. Dynamic light scattering (DLS) analysis showed that the liquid samples had uniform particle sizes and high stability. The liquid samples were tested for toxicity on Hep-G2 cancer cell lines and showed no toxicity on this cell line. The core/shell structured samples exhibited higher specific absorption rate (SAR) values than the individual core sample. Notably, the sample with the thickest shell achieved a SAR of 246.62 W/g, while the relaxation rate (r2) of the sample with the thinnest shell was 43.71 (mM s)−1. These initial results suggest our fabricated CoFe2O4/MnFe2O4 core/shell nanostructures exhibit potential biomedical applications, especially in magnetic hyperthermia treatment and magnetic resonance imaging (MRI) contrast enhancement. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles with an optimal size seek high inductive heating performance, which plays an important role in biomedical applications. This work reports the critical size of MnFe2O4 particles at which the specific absorption rate (SAR) reaches its maximum value. MnFe2O4 nanoparticles with different sizes from ~11 nm to ~70 nm were synthesized using the hydrothermal method. Under an applied field amplitude of 80 Oe and frequency of 236 kHz, the 18-nm MnFe2O4 nanoparticles exhibited the highest SAR of 65.52 W/g. The effective magnetic anisotropy, as a function of particle size, was used to calculate the theoretical value of SAR in the framework of the linear response theory. Experimental results agreed well with the theoretical calculations in the superparamagnetic regime. This study may serve as a basis for the accurate prediction of the optimal size of magnetic nanoparticles in inductive heating. [ABSTRACT FROM AUTHOR]