Nikolaos Maniotis

Nanocomposite rare-earth permanent magnets composed of exchange-coupled hard magnetic nanoparticles offer a promising route toward high-performance, rare-earth-efficient magnet technologies. In this work, we investigate the structural self-organization and magnetic hysteresis behavior of 40 nm Sm₂Co₁₇/Nd₂Fe₁₄B hybrid nanoparticles using a combined molecular dynamics (MD) and micromagnetic simulation framework. First, MD simulations are employed to study the Brownian motion and field-induced assembly of the hybrid nanoparticles at two particle concentrations (1 and 5 mg/cm³). In the absence of an external magnetic field, the nanoparticles display dispersed configurations governed by thermal fluctuations and interparticle interactions. Upon application of a high magnetic field (500 mT), the particles align into linear chain-like assemblies, with a more pronounced and rapid aggregation at higher concentration. Subsequently, micromagnetic calculations performed using the OOMMF are used to determine the magnetization reversal behavior of the assemblies. Quasi-static hysteresis loops at low field (40 mT) and room temperature reveal enhanced coercivity and remanence for field-aligned chain structures compared to randomly oriented particle ensembles. Additionally, increasing particle concentration amplifies the field-induced collective response due to stronger dipolar coupling. The combined MD–micromagnetic approach provides insight into structure–property relationships in magnetic nanocomposite systems and highlights the critical role of particle arrangement and concentration in determining magnet performance. These results contribute to the design principles for advanced nanostructured permanent magnets with tunable magnetic anisotropy and energy density.

Magnetic hyperthermia relies on the ability of magnetic nanoparticles (MNPs) to dissipate heat under alternating magnetic fields, with the heating efficiency commonly quantified through the specific loss power (SLP). Accurate estimation of SLP requires realistic modeling of the dynamic magnetic response of nanoparticle ensembles, particularly in the ferromagnetic single-domain regime where hysteresis losses dominate. In the present work, we developed a computational framework in Mathematica based on the thermally activated Stoner–Wohlfarth model to simulate dynamic hysteresis loops and estimate SLP in ensembles of non-interacting magnetic nanoparticles. The model incorporates experimentally relevant distributions of particle diameter, magnetic anisotropy, and easy-axis orientation, enabling realistic representation of nanoparticle polydispersity and orientation disorder. Thermal activation was introduced through Arrhenius-type Néel switching probabilities, while the dynamic magnetization evolution was obtained numerically through solution of the corresponding rate equations. The framework was tested for magnetite nanoparticles, one of the most widely used materials in magnetic hyperthermia, considering typical single-domain ferromagnetic particle sizes in the range of 15–30 nm and effective anisotropy K_eff values representative, 3 kJ/m³ < K_eff < 20 kJ/m³ of experimentally reported systems. Simulations were performed under clinically relevant alternating magnetic fields with amplitudes up to 24 kA/m and frequencies ranging from 100 to 765 kHz. The model successfully reproduced dynamic hysteresis loop evolution and enabled systematic investigation of the influence of nanoparticle size, anisotropy, and orientation distributions on loop shape, symmetry, and SLP. The developed code provides a computationally accessible tool for researchers working in magnetic hyperthermia, allowing direct connection between microscopic nanoparticle properties and macroscopic heating performance. By enabling parametric mapping of dynamic hysteresis behavior and SLP dependence, the framework may support the rational optimization of magnetic nanoparticle systems for biomedical hyperthermia applications.

Magnetic particle hyperthermia (MPH) is a rapidly advancing field with significant potential for biomedical applications; however, the interpretation and comparison of experimental and theoretical results remain challenging due to variability in nanoparticle properties, excitation conditions, and analysis methodologies. In this work, we introduce an open-access online toolbox developed to support education, data analysis, and experimental optimization in MPH research. The toolbox provides a unified framework for estimating key physical properties of magnetic nanoparticles (MNPs) as functions of size, magnetic anisotropy, and intrinsic material parameters. Its functionalities include: (i) determination of the specific loss power from temperature–time hyperthermia curves using an adiabatic approximation, incorporating systematic error estimation and sensitivity analysis; (ii) calculation of Néel and Brownian relaxation times, their effective combination, the imaginary component of dynamic magnetic susceptibility, and the corresponding relaxation losses; and (iii) estimation of hysteresis losses based on either experimental minor-loop measurements or theoretical dynamic hysteresis models. By enabling direct comparison between experimental data, theoretical predictions, and reference estimates, this toolbox enhances reproducibility, facilitates benchmarking, and supports the rational design and optimization of MNP systems, serving both as an educational resource and as a practical research tool for the magnetic hyperthermia community.

Magnetic hyperthermia relies on the ability of magnetic nanoparticles (MNPs) to dissipate heat under alternating magnetic fields, with the heating efficiency commonly quantified through the specific loss power (SLP). Accurate estimation of SLP requires realistic mod-eling of the dynamic magnetic response of nanoparticle ensembles, particularly in the fer-romagnetic single-domain regime where hysteresis losses dominate. In the present work, we developed a computational framework in Mathematica based on the thermally acti-vated Stoner–Wohlfarth model to simulate dynamic hysteresis loops and estimate SLP in ensembles of non-interacting magnetic nanoparticles. The model incorporates experimen-tally relevant distributions of particle diameter, magnetic anisotropy, and easy-axis orien-tation, enabling realistic representation of nanoparticle polydispersity and orientation disorder. Thermal activation was introduced through Arrhenius-type Néel switching probabilities, while the dynamic magnetization evolution was obtained numerically through solution of the corresponding rate equations. The framework was tested for mag-netite nanoparticles, one of the most widely used materials in magnetic hyperthermia, considering typical single-domain ferromagnetic particle sizes in the range of 15–30 nm and effective anisotropy values representative of experimentally reported systems. Simula-tions were performed under clinically relevant alternating magnetic fields with ampli-tudes up to 24 kA/m and frequencies ranging from 100 to 765 kHz. The model successfully reproduced dynamic hysteresis loop evolution and enabled systematic investigation of the influence of nanoparticle size, anisotropy, and orientation distributions on loop shape, symmetry, and SLP. The developed code provides a computationally accessible tool for re-searchers working in magnetic hyperthermia, allowing direct connection between micro-scopic nanoparticle properties and macroscopic heating performance. By enabling para-metric mapping of dynamic hysteresis behavior and SLP dependence, the framework may support the rational optimization of magnetic nanoparticle systems for biomedical hyper-thermia applications.

Correction for ‘A comprehensive analysis of nanomagnetism models for the evaluation of particle energy in magnetic hyperthermia’ by N. Maniotis et al. , Nanoscale Adv. , 2025, 7 , 4252–4269, https://doi.org/10.1039/D5NA00258C.

This work presents a micromagnetic investigation of monolayer L1₀ FePt and FePt/Fe bilayer thin films to clarify the role of thickness, composition, and exchange coupling in their magnetic behavior. Simulations were performed using the Landau–Lifshitz–Gilbert formalism implemented in OOMMF, with realistic material parameters and geometries. For FePt monolayers, film thicknesses of 1–20 nm were examined, revealing a non-monotonic coercivity trend: the coercive field increased from 35 mT at 1 nm to 136 mT at 10 nm and decreased to 69 mT at 20 nm. This evolution indicates a transition from localized reversal to domain-wall-mediated switching once the film exceeds the exchange length (10–20 nm). Additional simulations varying Fe concentration (48–68%) through the exchange stiffness constant showed that higher Fe content strengthens magnetic coupling and increases coercivity. Bilayer systems combining a 2 nm FePt layer with Fe layers of 10 and 12 nm exhibited rectangular, saturated loops, confirming strong exchange coupling and exchange-spring behavior. The results identify 2 nm FePt as the optimal thickness for achieving full saturation, balanced coercivity, and thermal stability in FePt/Fe thin-film architectures.

This study aims to identify optimal parameters for the clinical implementation of magnetic fields in therapeutic contexts, with a particular focus on in vitro magneto-mechanical actuation in biological systems. This approach relies on the transduction of magnetic energy into mechanical stress at low frequencies (<<100 Hz). Accordingly, the investigation centers on evaluating the magnetic field gradients responsible for initiating the motion of intracellular magnetic nanoparticles and the resulting mechanical forces acting upon them. To achieve this, a novel, custom-built, and highly adaptable three-dimensional turntable system was designed, calibrated, and implemented. This apparatus allows the generation of magnetic fields with precisely tunable amplitude and frequency, enabling controlled activation of magneto-mechanical mechanisms. In vitro experiments using this device facilitated the exposure of cancer cells to well-characterized magnetic fields, thereby inducing mechanical stimulation in the presence of nanoparticles distributed within intracellular or extracellular environments. Quantitative measurements of magnetic field intensities were performed, providing estimations of the forces exerted by magnetic nanoparticles with diverse physical characteristics (phase, size, and shape) under varying magnetic field gradients.

This work presents a micromagnetic investigation of monolayer L1₀ FePt and FePt/Fe bilayer thin films to clarify the role of thickness, composition, and exchange coupling in their magnetic behavior. Simulations were performed using the Landau–Lifshitz–Gilbert formalism implemented in OOMMF, with realistic material parameters and geometries. For FePt monolayers, film thicknesses of 1–20 nm were examined, revealing a non-monotonic coercivity trend: the coercive field increased from 35 mT at 1 nm to 136 mT at 10 nm and decreased to 69 mT at 20 nm. This evolution indicates a transition from localized reversal to domain-wall–mediated switching once the film exceeds the exchange length (10–20 nm). Additional simulations varying Fe concentration (48–68%) through the exchange stiffness constant showed that higher Fe content strengthens magnetic coupling and increases coercivity. Bilayer systems combining a 2 nm FePt layer with Fe layers of 10 and 12 nm exhibited rectangular, saturated loops, confirming strong exchange coupling and exchange-spring behavior. The results identify 2 nm FePt as the optimal thickness for achieving full saturation, balanced coercivity, and thermal stability in FePt/Fe thin-film architectures.

Magnetic nanoparticles have attracted significant research interest due to their unique magnetic properties, which differ from their bulk counterparts and enable applications in information technology, environmental protection, and biomedicine.