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

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

Gijon

Conferencia; International Conference on Fine Particle Magnetism; 2019

Universidad de Oviedo

This key point in magnetic fluid hyperthermia is the dominant mechanism in the relaxation of the magnetic moment, which determines the out-of-phase susceptibility in the presence of an ac magnetic field and consequently the power absorption. Those mechanisms are the viscous one, related with the Brownrelaxation time, and the magnetic anisotropy one, related with the Neel relaxation time. The properties that address the dominant relaxation mechanism are the medium viscosity and the anisotropy energy barrier. The design of systems with controlled magnetic properties aim at controlling completely the response of a magnetic fluid in hyperthermia experiments. Here we report a simple and effective way to control the heat generation of a magnetic colloid in magnetic hyperthermia by using the core-shell architecture for bimagnetic nanosystems, with two magnetic phases magnetically-coupled. Firstly, the magnetic properties are controlled by changing the shell composition of bimagnetic core?shell Fe 3 O 4 /Zn x Co 1−x Fe 2 O 4 nanoparticles, with an effective anisotropy that can be tuned by the substitution of Co 2+ by Zn 2+ ions in the shell, with keeping a relatively high saturation magnetization. Magnetic hyperthermia experiments of these nanoparticles dispersed in hexane and butter oil showed that the magnetic relaxation is dominated by Brown relaxation 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 Zn concentration of the shell, diminishes the magnetic anisotropy, which results in a change to a Néel relaxation that dominates the process when the nanoparticles are dispersed in a high viscosity medium. We demonstrate that 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 essential prerequisite for most biomedical applications, where high viscosities and capturing mechanisms are present. Based on these results, we design core-shell Fe 3 O 4 /Zn x Co 1−x Fe 2 O 4 nanoparticles with high response in magnetic hyperthermia experiments even in the butter oil as consequence of a viscosity-independent dominant magnetic relaxation mechanism.