Microscopic theory of the specific absorption rate for self-controlled magnetic hyperthermia

Abstract

Despite the efforts of many research teams, to optimize the process of thermal heating of magnetic nanoparticles interacting with an alternating magnetic field for self-controlled magnetic hyperthermia remains a challenge. Macroscopic models that quantify the process of heat generation could not combine the biocompatibility requirements of magnetic nanoparticles in human medicine on one hand with high values of specific absorption rate (SAR) on the other. For the first time, we propose a microscopic model using Kubo formalism, a modified Heisenberg Hamiltonian and the method of Green's functions for calculating the absorbed power (thermal energy absorbed by a magnetic nanoparticle per unit time in an alternating magnetic field). From the observed transverse magnetic susceptibility, elementary excitation energy, and damping is investigated the SAR as a function of the microscopic parameters of the systems: exchange interaction constants and single-ion magnetic anisotropy. The calculations are made for a magnetic complex heterogeneous nanoparticle consisting of core, shell, intermediate layer between them, and surface (the so called core/shell model). The proposed nanoparticle model allows for each region to define different exchange interaction and magnetic anisotropy constants as well as different magnetic configurations and thickness. The dependence of SAR on the microscopic parameters of the system is analyzed and qualitatively explained by the behavior of the elementary excitations (spin energy and damping). The results are in good qualitative agreement with the experimental data and show that using complex magnetic nanoparticles the heating properties for hyperthermia could be maximized.