Controlling the dominant magnetic relaxation mechanisms for magnetic hyperthermia in bimagnetic core?shell nanoparticles

DE BIASI, EMILIO; MANSILLA, MARCELO VÁSQUEZ; IBARRA, M. RICARDO; WINKLER, ELIN; ENIO LIMA JR; HORACIO E. TROIANI; FERNANDEZ-PACHECO, RODRIGO; ROBERTO D ZYSLER; FABRIS, FERNANDO; LOHR, JAVIER; TORRES MOLINA, TEOBALDO ENRIQUE; GERARDO F GOYA

Gijon

Conferencia; 10th International Conference on Fine Particles Magnetism; 2019

Universidad de Oviedo

The key point in magnetic fluid hyperthermia is the dominant mechanism in the relaxation of themagnetic moment, which determines the out-of-phase susceptibility in the presence of an AC magnetic fieldand consequently the power absorption. Those mechanisms are the viscous one, related with the Brownrelaxation time, and the magnetic anisotropy one, related with the Néel relaxation time. The properties thataddress the dominant relaxation mechanism are the medium viscosity and the anisotropy energy barrier. Thedesign of systems with tuned magnetic properties aim at controlling completely the response of a magneticfluid in hyperthermia experiments [1]. Here we report a simple and effective way to control the heatgeneration of a magnetic colloid in magnetic hyperthermia by using the core-shell architecture forbimagnetic nanosystems, with two magnetic phases magnetically-coupled. Firstly, the magnetic propertiesare controlled by changing the shell composition of bimagnetic core?shell Fe3O4/ZnxCo1−xFe2O4nanoparticles, with an effective anisotropy that can be tuned by the substitution of Co2+ by Zn2+ ions in theshell, with keeping a relatively high saturation magnetization. Magnetic hyperthermia experiments of thesenanoparticles dispersed in hexane and butter oil showed that the magnetic relaxation is dominated by Brownrelaxation mechanism in samples with higher anisotropy (i.e., larger concentration of Co within the shell)yielding high specific power absorption values in low viscosity media as hexane. Increasing the Znconcentration of the shell, diminishes the magnetic anisotropy, which results in a change to a Néel relaxationthat dominates the process when the nanoparticles are dispersed in a high viscosity medium. We demonstratethat tuning the Zn contents at the shell of these exchange-coupled core/shell nanoparticles provides a way tocontrol the magnetic anisotropy without loss of saturation magnetization. This ability is an essentialprerequisite for most biomedical applications, where high viscosities and capturing mechanisms are present.Based on these results, we design core-shell Fe3O4/ZnxCo1−xFe2O4 nanoparticles with high response inmagnetic hyperthermia experiments even in the butter oil as con