Size-Dependent Magnetic Heating of MnFe₂O₄ Nanoparticles

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.