The effect of the particle size on the heating and drug release potential of the magnetic nanoparticles in a novel point of view

The present study is written to provide an overview of the effect of the particle size on the heating and drug release potential of the magnetic materials under magnetic fields. As a symbol representing the change of particle size, a dimensionless σ parameter is defined by dividing anisotropic energy by the thermal one. According to the obtained results, at the boundary of ferromagnetic and superparamagnetic nanoparticles (σ≈1), there is the maximum heat production. On the other hand, single-domain nanoparticles with the largest size (σ≫1) have the lowest releasing heat under AC magnetic field. There is also a considerable heat production under AC magnetic fields for both superparamagnetic (σ < 1) and soft-ferromagnetic materials (σ > 1). However, the results are significantly different when MNPs are used as heating cores in drug release systems. Here, the soft-ferromagnetic materials have a low heating and hence low drug release potential. According to the results obtained, increasing σ causes three important events. The first is the reduction of the spin canting effect which results in the amplification of the spin rotations in the same direction and hence a higher potential of Neel heating mechanism. The second is the growth of the macrospin size which leads to more spin torque and hence more heating energy. The third is blocking the macrospin and consequently activation of the Brownian heating mechanism. However, the results are significantly different when MNPs are used as heating cores in drug release systems. Here, the soft-ferromagnetic materials have a low heating and hence low drug release potential. As a reason one can say that in drug release systems, there are barriers to activation of the Brownian mechanism which reduce the heating and drug release potential of soft-ferromagnetic nanoparticles.