Estimating the effective anisotropy of ferromagnetic nanoparticles through magnetic and calorimetric simulations

Abstract

Magnetic nanoparticle-mediated hyperthermia holds great promise as a treatment for cancer. The key measure used for characterizing the heating efficiency of nanoparticles in this context is the specific loss power, which may be derived from the magnetic hysteresis loop area. An intrinsic property of magnetic nanoparticles that influences specific loss power is magnetic anisotropy, which is difficult to estimate because of its complicated nature. This work presents a simple method for the theoretical estimation of magnetic anisotropy in ferromagnetic magnetite nanoparticles of 40 nm diameter. We conduct numerical calculations of hysteresis loops, employing a Monte Carlo technique for a typical anisotropy range of 2 to 11 kJ/m3. To assess the validity of our simulations and to estimate the optimum anisotropy for our magnetic nanoparticles, we compare numerically estimated loops with an experimental one. Using the finite element method, we perform heat transfer simulations to calculate temporal temperature distributions in an aqueous dispersion of magnetic nanoparticles for a fixed range of anisotropy values. Simulated heating curves are compared with experimental ones to verify magnetic nanoparticle anisotropy, which coincides with the one obtained from the above Monte Carlo simulations and is equal to 9 kJ/m3. Therefore, in this study, we propose a rigorous quantification of the anisotropy of ferromagnetic nanoparticles both magnetically and calorimetrically through hysteresis loop estimation and heat transfer simulations, respectively, so that their specific loss power can be accurately determined and used for treatment planning in clinical practice.