From Micromagnetic to In Silico Modeling of Magnetic Nanodisks for Hyperthermia Applications

Magnetic nanodisks have been recently proposed as biomedical tools for therapeutics at the nanoscale level, with a special focus on hyperthermia for cancer cure. Here we present a detailed study of permalloy nanodisks to be used in alternative to superparamagnetic iron oxide nanoparticles, as efficient heating agents that release heat via magnetic hysteresis. A micromagnetic modeling analysis is carried out to identify sizes and ac field parameters that maximize the specific loss power (SLP), guaranteeing the fulfillment of biophysical constraints (Hergt–Dutz limit) and vortex state at remanence (reduced agglomeration effects). The highest SLP (790 W g−1) is found for 100 nm diameter and 20 nm thickness nanodisks, excited at a frequency of 75 kHz. Further analysis elucidates the influence of magnetostatic interactions and local nanodisk-field orientation on the SLP of nanodisk clusters, which originate from the deposition in target tissues. At high concentrations, magnetostatic interactions can lead to a reduction of 40–50% in the hysteresis losses. From thermal simulations, we finally demonstrate that in a murine model temperature increments comparable to that obtained in calorimetric measurements under quasi-adiabatic conditions can be achieved only by using an order of magnitude larger dosage of nanodisks, due to blood perfusion effects

Application of Magnonic Crystals in Magnetic Bead Detection

This paper aims at studying a sensor concept for possible integration in magnetic field-based lab-on-chip devices that exploit ferromagnetic resonance (FMR) phenomena in magnonic crystals. The focus is on 2D magnetic antidot arrays, i.e., magnetic thin films with periodic non-magnetic inclusions (holes), recently proposed as magnetic field sensor elements operating in the gigahertz (GHz) range. The sensing mechanism is here demonstrated for magnetic nano/microbeads adsorbed on the surface of permalloy (Ni80Fe20) antidot arrays with a rhomboid lattice structure and variable hole size. Through extensive micromagnetic modelling analysis, it is shown that the antidot arrays can be used as both bead traps and high-sensitivity detectors, with performance that can be tuned as a function of bead size and magnetic moment. A key parameter for the detection mechanism is the antidot array hole size, which affects the FMR frequency shifts associated with the interaction between the magnetization configuration in the nanostructured film and the bead stray field. Possible applications of the proposed device concept include magnetic immunoassays, using magnetic nano/microbeads as probes for biomarker detection, and biomaterial manipulation

Influence of size, volume concentration and aggregation state on magnetic nanoparticle hyperthermia properties versus excitation conditions

Treatment planning in magnetic hyperthermia requires a thorough knowledge of specific loss power of magnetic nanoparticles as a function of size and excitation conditions. Moreover, in biological tissues the magnetic nanoparticles can aggregate into clusters, making the evaluation of their heating performance more challenging because of the magnetostatic dipole–dipole interactions. In this paper, we present a comprehensive modelling analysis of 10–40 nm sized spherical magnetite (Fe3O4) nanoparticles, investigating how their heating properties are influenced by magnetic field parameters (peak amplitude and frequency), and by volume concentration and aggregation state. The analysis is performed by means of an in-house micromagnetic numerical model, which solves the Landau–Lifshitz–Gilbert equation under the assumption of single-domain nanoparticles, including thermal effects via a Langevin approach. The obtained results provide insight into how to tune hyperthermia properties by varying magnetic nanoparticle size, under different excitation magnetic fields fulfilling the Hergt–Dutz limit (frequency between 50 kHz and 1 MHz, and peak amplitude between 1 kA m−1 and 50 kA m−1). Special attention is finally paid to the role of volume concentration and aggregation order, putting in evidence the need for models able to account for stochasticity and clustering in spatial distribution, to accurately simulate the contribution of magnetostatic dipole–dipole interactions in real applications

Private Colleges, State Aid, and the Establishment Clause

Using local scanning electrical techniques we study edge effects in side-gated Hall bar nanodevices made of epitaxial graphene. We demonstrate that lithographically defined edges of the graphene channel exhibit hole conduction within the narrow band of similar to 60-125 nm width, whereas the bulk of the material is electron doped. The effect is the most pronounced when the influence of atmospheric contamination is minimal. We also show that the electronic properties at the edges can be precisely tuned from hole to electron conduction by using moderate strength electrical fields created by side-gates. However, the central part of the channel remains relatively unaffected by the side-gates and retains the bulk properties of graphene.Funding Agencies|NMS under the IRD Graphene Project (NPL); EMRP</p

Modeling analysis of the electromagnetic braking action on rotating solid cylinders

AbstractThe electromagnetic diffusion and the electromechanical phenomena arising in a solid cylinder rotating inside a magnetic field are here analyzed. The study is developed through a time stepping Finite Element voltage-driven formulation, employing the sliding mesh technique for handling the cylinder motion. The influence on the dynamic behavior and energy dissipation of the material electric and magnetic properties, the geometrical parameters and the supply conditions is investigated considering a model problem

In silico experiments as a tool to reduce preclinical tests of magnetic hyperthermia

In silico models can be useful tools to guide preclinical tests of magnetic hyperthermia, which employs Magnetic Nanoparticles (MNPs) excited by AC magnetic fields, as heat mediators for cancer cure. We virtually reproduce the heating process induced by magnetic hyperthermia in murine models, as a function of field applicator features, properties and size of target tissue, MNP dose and animal size

Influence of lattice defects on the ferromagnetic resonance behaviour of 2D magnonic crystals

This paper studies, from a modelling point of view, the influence of randomly distributed lattice defects (non-patterned areas and variable hole size) on the ferromagnetic resonance behaviour and spin wave mode profiles of 2D magnonic crystals based on Ni80Fe20 antidot arrays with hexagonal lattice. A reference sample is first defined via the comparison of experimental and simulated hysteresis loops and magnetoresistive curves of patterned films, prepared by self-assembly of polystyrene nanospheres. Second, a parametric analysis of the dynamic response is performed, investigating how edge, quasi-uniform and localized modes are affected by alterations of the lattice geometry and bias field amplitude. Finally, some results about the possible use of magnetic antidot arrays in frequency-based sensors for magnetic bead detection are presented, highlighting the need for an accurate control of microstructural features