Specific absorption rate of uniaxial single-domain nanomagnets: stochastic spin dynamics versus linear response theory
Year: 2026
Type: preprint
Abstract: We compute the specific absorption rate of a uniaxial single-domain nanomagnet driven by an alternating magnetic field by two methods: i) direct numerical integration of the stochastic (Langevin) Landau--Lifshitz--Gilbert equation (the LLL approach), and ii) linear response theory (LRT) based on the Debye susceptibility with the Néel relaxation time $\ta$. We first analytically show that both methods are equivalent for small magnetic field amplitude, and then compute their deviation $Λ\equiv\SAR_{\LLL}/\SAR_{\LRT}-1$ as a function of the magnetic field amplitude for two temperatures chosen on opposite sides of the Debye resonance. One of the main results is that the sign and magnitude of $Λ$ are governed by the dimensionless product $\om\ta$, in addition to the linearity parameter $ξ=μ_{s}B_{0}/k_{B}T$ for the easy-axis geometry considered here. Indeed, below resonance ($\om\ta<1$), linear response theory overestimates the specific absorption rate, whereas above resonance ($\om\ta>1$, the regime typical of blocked nanoparticles) linear response theory can underestimate the specific absorption rate by up to $\sim70\%$ at $ξ\sim2$. We expect this work to provide a quantitative guidance for the use of linear response theory in magnetic hyperthermia and related nanoscale heat-transport problems, and to serve as a single-particle benchmark for extensions to many-spin and interacting systems.
Source: arXiv (Cornell University)
Author: Kachkachi, H.
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7166067854