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

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

Influence of shape, size and magnetostatic interactions on the hyperthermia properties of permalloy nanostructures

We present a detailed study of permalloy (Ni80Fe20) nanostructures with variable shape (disk, cylinder and sphere) for magnetic hyperthermia application, exploiting hysteresis losses for heat release. The study is performed modifying nanostructure aspect ratio and size (up to some hundreds of nanometres), to find the optimal conditions for the maximization of specific heating capabilities. The parameters are also tuned to guarantee negligible magnetic remanence and fulfilment of biophysical limits on applied field amplitude and frequency product, to avoid aggregation phenomena and intolerable resistive heating, respectively. The attention is first focused on disk-shaped nanostructures, with a comparison between micromagnetic simulations and experimental results, obtained on nanodisks still attached on the lithography substrate (2D array form) as well as dispersed in ethanol solution (free-standing). This analysis enables us to investigate the role of magnetostatic interactions between nanodisks and to individuate an optimal concentration for the maximization of heating capabilities. Finally, we study magnetization reversal process and hysteresis properties of nanocylinders (diameter between 150 nm and 600 nm, thickness from 30 nm up to 150 nm) and nanospheres (size between 100 nm and 300 nm), to give instructions on the best combination of geometrical parameters for the design of novel hyperthermia mediators

Hybrid normal metal/ferromagnetic nanojunctions for domain wall tracking

Hybrid normal metal/ferromagnetic, gold/permalloy (Au/Py), nanojunctions are used to investigate magnetoresistance effects and track magnetization spatial distribution in L-shaped Py nanostructures. Transversal and longitudinal resistances are measured and compared for both straight and 90° corner sections of the Py nanostructure. Our results demonstrate that the absolute change in resistance is larger in the case of longitudinal measurements. However, due to the small background resistance, the relative change in the transversal resistance along the straight section is several orders of magnitude larger than the analogous longitudinal variation. These results prove that hybrid nanojunctions represent a significant improvement with respect to previously studied all-ferromagnetic crosses, as they also reduce the pinning potential at the junction and allow probing the magnetization locally. In addition, unusual metastable states with longitudinal domain walls along Py straight sections are observed. Micromagnetic simulations in combination with a magnetotransport model allow interpretation of the results and identification of the observed transitions