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

Nanomaterials Characterisation through Magnetic Field Dependent AFM

Atomic force microscopy is a versatile technique allowing to exploit many different physical effects for measuring a number of materials properties. The magnetic properties of surfaces and thin films are traditionally accessed through magnetic force microscopy, which produces magnetic field gradient maps generated by the magnetisation distribution at the surface of the sample. However, more advanced techniques can be derived from this fundamental setup, allowing for a richer characterisation of magnetic samples. In this chapter, we will describe how to extend a magnetic force microscope to allow magnetic field-dependent characterisations. Magnetisation reversal processes, as well as full hysteresis loops, can be investigated with such a technique, with field resolution adequate for identifying significant features such as domains reversal, nucleation or annihilation of domains, and other irreversible mechanisms. The same principle can also be exploited for the measurement of magnetostriction on thin films, and can be taken as guideline for other advanced applications of atomic force microscopy

Measurement of thin film magnetostriction using field-dependent atomic force microscopy

Measurement of thin film magnetostriction is a challenging task, as magnetostrictive material deformations in parts per million, in conjunction with materials at small dimensions, require high precision, often with dedicated set-ups, for reproducible results. We have developed a novel approach employing a commercial atomic force microscope (AFM) with attached electromagnets. Magnetostriction measurements are demonstrated on 50 - 500 nm thick Fe81Al19 films sputter deposited directly on high aspect ratio commercial AFM micro-cantilevers. A magnetostrictive deflection of the cantilever bimorph translates into a deflection force acting in a contact mode measurement, which is interpreted and recorded as a change in height. For determination of the magnetostriction coefficient, we have developed a modified version of the equation for the magnetostrictive deflection of a cantilever bimorph by Guerrero and Wetherhold, taking into account long-range attractive forces acting during contact mode AFM measurements in air. The sub-atomic precision of the AFM, combined with the widespread availability of all components and the simple set-up, makes the measurement of magnetostriction on films of just a few tens of nanometers thickness easily accessible.H2020-MSCA-ITN-2014 SELECTA (grant agreement no. 642642 of the European Commission

Increase of telomerase activity and hTERT expression in myelodysplastic syndromes

Telomerase enzyme, containing a catalytic subunit, the human telomerase reverse transcriptase (hTERT), and a small integral RNA component, synthesises the telomeres, the ends of eukaryotic chromosomes. Inhibition of telomerase activity leads the cells to senescence and death. Myelodysplastic syndromes (MSD) are hematological malignancies characterized by peripheral blood cytopenia and ineffective hematopoiesis. Telomerase activity and hTERT expression in MDS patients were independently investigated by different groups obtaining contradictory results. We analyzed telomerase activity and hTERT expression in the bone marrow of ten control, 15 MDS patients and two patients with AML, likely evolved from a previous MDS. Moreover, the expression of c-myc, mad1, p53 (transcription factors involved in hTERT expression regulation), has been investigated. Telomerase activity and hTERT expression increased in the MDS patients with respect to the controls. The analysis of the MDS subgroups, indicated that patients with more severe disease demonstrated significantly higher levels of hTERT expression and telomerase activity with respect to the patients with more favorable disease. c-Myc and p53 expressions were not significantly different between controls and MDS patients, whereas mad1 expression was increased in MDS patiens, particularly in those with more favorable disease. We hypothesize that mad1 increase can contribute to reduce the hTERT expression in the early stage of disease and we suggest that hTERT expression and telomerase activity, whether confirmed in larger series of cases could support other parameters in the diagnosis and stadiation of MDS

Experimental and Modelling Analysis of the Hyperthermia Properties of Iron Oxide Nanocubes

open10sìThe ability of magnetic nanoparticles (MNPs) to transform electromagnetic energy into heat is widely exploited in well-known thermal cancer therapies, such as magnetic hyperthermia, which proves useful in enhancing the radio- and chemo-sensitivity of human tumor cells. Since the heat release is ruled by the complex magnetic behavior of MNPs, a careful investigation is needed to understand the role of their intrinsic (composition, size and shape) and collective (aggregation state) properties. Here, the influence of geometrical parameters and aggregation on the specific loss power (SLP) is analyzed through in-depth structural, morphological, magnetic and thermometric characterizations supported by micromagnetic and heat transfer simulations. To this aim, different samples of cubic Fe3O4 NPs with an average size between 15 nm and 160 nm are prepared via hydrothermal route. For the analyzed samples, the magnetic behavior and heating properties result to be basically determined by the magnetic single- or multi-domain configuration and by the competition between magnetocrystalline and shape anisotropies. This is clarified by micromagnetic simulations, which enable us to also elucidate the role of magnetostatic interactions associated with locally strong aggregation.openhttps://zenodo.org/record/5040394#.YhVWyejMKUkFerrero, R; Barrera, G; Celegato, F; Vicentini, M; Sozeri, H; Yildiz, N; Dincer, CA; Coisson, M; Manzin, A; Tiberto, PFerrero, R; Barrera, G; Celegato, F; Vicentini, M; Sozeri, H; Yildiz, N; Dincer, Ca; Coisson, M; Manzin, A; Tiberto,

Control of magnetic vortex states in FeGa microdisks : Experiments and micromagnetics

Magnetic vortices have been an interesting element in the past decades due to their flux-closure domain structures which can be stabilized at ground states in soft ferromagnetic microstructures. In this work, vortex states are shown to be nucleated and stabilized in FeGa and FeGa disks, which can be an upcoming candidate for applications in strain-induced electric field control of magnetic states owing to the high magnetostriction of the alloy. The magnetization reversal in the disks occurs by the formation of a vortex, double vortex or S-domain state. Micromagnetic simulations have been performed using the FeGa material parameters and the simulated magnetic states are in good agreement with the experimental results. The studies performed here can be essential for the use of FeGa alloy in low-power electronics

Electrochemical Synthesis, Magnetic and Optical Characterisation of FePd Dense and Mesoporous Nanowires

Dense and mesoporous FePd nanowires (NWs) with 45 to 60 at.% Pd content were successfully fabricated by template- and micelle-assisted pulsed potentiostatic electrodeposition using nanoporous anodic alumina and polycarbonate templates of varying pore sizes. An FePd electrolyte was utilized for obtaining dense NWs while a block copolymer, P-123, was added to this electrolyte as the micelle-forming surfactant to produce mesoporous NWs. The structural and magnetic properties of the NWs were investigated by electron microscopy, X-ray diffraction, and vibrating sample magnetometry. The as-prepared NWs were single phase with a face-centered cubic structure exhibiting 3.1 µm to 7.1 µm of length. Mesoporous NWs revealed a core-shell structure where the porosity was only witnessed in the internal volume of the NW while the outer surface remained non-porous. Magnetic measurements revealed that the samples displayed a soft ferromagnetic behavior that depended on the shape anisotropy and the interwire dipolar interactions. The mesoporous core and dense shell structure of the NWs were seen to be slightly affecting the magnetic properties. Moreover, mesoporous NWs performed excellently as SERS substrates for the detection of 4,4'-bipyridine, showing a low detection limit of 10 −12 M. The signal enhancement can be attributed to the mesoporous morphology as well as the close proximity of the embedded NWs being conducive to localized surface plasmon resonance

A comparative study of the influence of the deposition technique (electrodeposition versus sputtering) on the properties of nanostructured Fe70Pd30 films

Sputtering and electrodeposition are among the most widespread techniques for metallic thin film deposition. Since these techniques operate under different principles, the resulting films typically show different microstructures even when the chemical composition is kept fixed. In this work, films of Fe70Pd30 were produced in a thickness range between 30 and 600 nm, using both electrodeposition and sputtering. The electrodeposited films were deposited under potentiostatic regime from an ammonia sulfosalicylic acid-based aqueous solution. Meanwhile, the sputtered films were deposited from a composite target in radio frequency regime. Both approaches were proven to yield high quality and homogenous films. However, their crystallographic structure was different. Although all films were polycrystalline and Fe and Pd formed a solid solution with a body-centered cubic structure, a palladium hydride phase was additionally detected in the electrodeposited films. The occurrence of this phase induced internal stress in the films, thereby influencing their magnetic properties. In particular, the thickest electrodeposited Fe70Pd30 films showed out-of-plane magnetic anisotropy, whereas the magnetization easy axis lied in the film plane for all the sputtered films. The domain pattern of the electrodeposited films was investigated by magnetic force microscopy. Finally, nanoindentation studies highlighted the high quality of both the sputtered and electrodeposited films, the former exhibiting higher reduced Young’s modulus and Berkovich hardness values