Specific absorption rate of uniaxial single-domain nanomagnets: stochastic spin dynamics versus linear response theory
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≡SARLLL/SARLRT−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 omta, in addition to the linearity parameter ξ=μsB0/kBT for the easy-axis geometry considered here. Indeed, below resonance (omta<1), linear response theory overestimates the specific absorption rate, whereas above resonance (omta>1, the regime typical of blocked nanoparticles) linear response theory can underestimate the specific absorption rate by up to ∼70% at ξ∼2. 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.
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BibTeX
@misc{kachkachi2026specific,
title = {{Specific absorption rate of uniaxial single-domain nanomagnets: stochastic spin dynamics versus linear response theory}},
author = {H. Kachkachi},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2606.27351},
eprint = {2606.27351},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.27351},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Specific absorption rate of uniaxial single-domain nanomagnets: stochastic spin dynamics versus linear response theory
AU - H. Kachkachi
PY - 2026
DA - 2026/11/04
PB - arXiv
DO - 10.48550/arxiv.2606.27351
UR - https://arxiv.org/abs/2606.27351
AB - 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≡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 omta, in addition to the linearity parameter ξ=μ_sB_0/k_BT for the easy-axis geometry considered here. Indeed, below resonance (omta<1), linear response theory overestimates the specific absorption rate, whereas above resonance (omta>1, the regime typical of blocked nanoparticles) linear response theory can underestimate the specific absorption rate by up to ∼70% at ξ∼2. 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.
ER -