To Heat or not to Heat: a Study of the Performances of Iron Carbide Nanoparticles in Magnetic Heating

TL;DR

This study investigates why iron carbide nanoparticles exhibit vastly different heating efficiencies under magnetic fields, linking their surface chemistry and chain formation ability to their heating performance, and proposes a model for their heating mechanism.

Contribution

It introduces a novel model explaining the heating mechanism of FeC nanoparticles, emphasizing the role of chain formation and surface ligand effects, supported by time-dependent magnetic measurements.

Findings

Larger heating power correlates with time-dependent hysteresis area increase.

Nanoparticle chain formation under magnetic excitation enhances heating efficiency.

Surface ligand concentration influences dipolar coupling and chain formation.

Abstract

Heating magnetic nanoparticles with high frequency magnetic fields is a topic of interest for biological applications (magnetic hyperthermia) as well as for heterogeneous catalysis. This study shows why FeC NPs of similar structures and static magnetic properties display radically different heating power (SAR from 0 to 2 kW.g-1). By combining results from Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and static and time-dependent high-frequency magnetic measurements, we propose a model describing the heating mechanism in FeC nanoparticles. Using, for the first time, time-dependent high-frequency hysteresis loop measurements, it is shown that in the samples displaying the larger heating powers, the hysteresis is strongly time dependent. More precisely, the hysteresis area increases by a factor 10 on a timescale of a few tens of seconds. This effect is directly related to the ability of the nanoparticles to form chains under magnetic excitation, which depends on the presence or not of strong dipolar couplings. These differences are due to different ligand concentrations on the surface of the particles. As a result, this study allows the design of a scalable synthesis of nanomaterials displaying a controllable and reproducible SAR.