Regular Article

Specific absorption rate in Zn-doted ferrites for self-controlled magnetic hyperthermia

¹ University of Architecture, Civil Engineering and Geodesy, Faculty of Hydrotechnics, Department of Physics, Hr. Smirnenski Blvd. 1, 1046 Sofia, Bulgaria
² University of Forestry, Faculty of Forest Industry, Kl. Ohridsky Blvd. 10, 1756 Sofia, Bulgaria
³ University of Sofia, Department of Physics, J. Bouchier Blvd. 5, 1164 Sofia, Bulgaria

^a e-mail: angelapos@abv.bg

Received: 24 September 2018
Received in final form: 8 December 2018
Published online: 11 March 2019

Abstract

In this paper, we study mixed ferrites nanoparticles with structure formula Me_1−xZn_xFe₂O₄ (Me = Co, Ni, Cu, Mn) appropriated for self-controlled magnetic hyperthermia (SMHT) for in vivo and in vitro applications. We discuss in details the influence of the size d, the Zn-ion concentration x on the magnetic characteristics: saturation magnetization M_S, coercivity H_C, effective anisotropy K_eff and specific absorption rate (SAR). From a theoretical point of view we investigate monodispersed, non-interactive, single-domain spherical magnetic nanoparticles (MNPs). We propose a simple core–shell model with a constant thickness of the surface layer. We explain the behaviour of SAR as a function of size and dopping based on two thermal heating mechanisms: the mechanism leading to dynamic hysteresis loops of superparamagnetic origin and the heating mechanism via conventional metastable hysteresis. We investigate also a thermal heating efficiency based on the Zn-ion concentration. We show that whether SAR decreases (increases) when doping increases depends on whether the nanoparticle diameter d is smaller (larger) than the particle size d_max for which SAR has a maximum value. The numerical results are in qualitative agreement with many experimental data.