Analysis of the magnetic properties of core-shell iron oxide nanoparticles

Abstract

We report on the magnetization of core-shells nanoparticles. Magnetic nanoparticles with a core of magnetite of 13 nm diameter covered with a shell of dopamine (1.1 nm thickness) are studied through vibrating sample magnetometer (VSM), Monte Carlo (MC) computer simulations, and analytical equations. All parameters involved in the theoretical analysis are experimentally determined, namely, the magnetic moment, temperature, magnetic field, core diameter, shell thickness, magnetic anisotropy, and particle concentration. The dependence of the magnetization with the magnetic field obtained through VSM and MC shows a 1% discrepancy in the magnetic saturation and up to 40% in the initial magnetic susceptibility. However, the dependence of the magnetization with the temperature obtained by MC indicates that the MNPs obey the Curie law above a critical temperature of 100 K, and dipolar interactions play an important role in the interval 20 < T < 100 K. That critical temperature is very close to the blocking temperature measured following the zero-field-cooled and zero-cooled protocols, where the dipolar interactions between MNPs become significant. Further analysis shows a Langevin-like behavior for both experimental and theoretical magnetizations.