Time profile of temperature rise in assemblies of nanomagnets

TL;DR

This paper models the temperature increase in nanomagnet assemblies under alternating magnetic fields, analyzing heat generation, transfer, and effects of frequency and amplitude, with implications for magnetic hyperthermia applications.

Contribution

It provides an analytical and numerical framework for understanding heat dynamics in nanomagnet assemblies under AMF, incorporating experimental data to explore heat transfer coefficients.

Findings

Analytical solutions closely match numerical results.

Temperature rise depends on AMF frequency and amplitude.

Insights into heat transfer coefficients in ferrofluids.

Abstract

We compute the heat generated by (non-interacting) nanomagnets subjected to an alternating magnetic field (AMF) and study its transfer to the hosting medium and environment. For the first task, we compute the heat generated by the nanomagnets (or the specific absorption rate) using the ac susceptibility in the linear regime. For the second task, the loss of heat to the environment is modeled with the help of a balance (macroscopic) equation based on Newton's law of cooling. This equation is solved both numerically and analytically for a generic ferrofluid and the analytical solution renders a very good approximation to the general balance equation. Then, we investigate the effects of AMF frequency and amplitude on the temperature elevation during its temporal evolution. Finally, using the available experimental data for maghemite and magnetite ferrofluids, we discuss the behavior of Newton's heat transfer coefficient in terms of the AMF amplitude and frequency. These results could trigger experimental investigations of this coefficient which characterizes the rate of heating in a ferrofluid, with the aim to build more refined models for the mechanisms of heat generation and its diffusion in ferrofluids used in magnetic hyperthermia.