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

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

Au-Coated Ni80Fe20 Submicron Magnetic Nanodisks: Interactions With Tumor Cells

Effective interaction and accumulation of nanoparticles (NPs) within tumor cells is crucial for NP-assisted diagnostic and therapeutic biomedical applications. In this context, the shape and size features of NPs can severely influence the strength of adhesion between NPs and cell and the NP internalization mechanisms. This study proved the ability of the PT45 and A549 tumor cells to uptake and retain magnetic Au-coated Ni80Fe20 nanodisks (NDs) prepared by means of a bottom–up self-assembling nanolithography technique assisted by polystyrene nanospheres. The chosen geometrical parameters, i.e., diameter (≈650 nm) and thickness (≈30 nm), give rise to magnetic domain patterns arranged in vortex state at the magnetic remanence. PT45 and A549 cell lines were cultured in the presence of different concentrations of Au-coated Ni80Fe20 nanodisks, and their biocompatibility was evaluated by viability and proliferation tests. Electron microscopy techniques and a combined CARS (Coherent Anti-stokes Raman Scattering) and TPL (two-photon photoluminescence) microscopy allow localizing and distinguishing the NDs within or attached to the tumor cells, without any labeling. A quantitative measurement of ND amount retained within tumor cells as a function of ND concentrations was performed by the Instrumental Neutron Activation Analysis (INAA) characterization technique

Strain‐Driven Bidirectional Spin Orientation Control in Epitaxial High Entropy Oxide Films

High entropy oxides (HEOs), based on the incorporation of multiple-principal cations into the crystal lattice, offer the possibility to explore previously inaccessible oxide compositions and unconventional properties. Here it is demonstrated that despite the chemical complexity of HEOs external stimuli, such as epitaxial strain, can selectively stabilize certain magneto-electronic states. Epitaxial (Co$_{0.2}$Cr$_{0.2}$Fe$_{0.2}$Mn$_{0.2}$Ni$_{0.2}$)$_{3}$O$_{4}$-HEO thin films are grown in three different strain states: tensile, compressive, and relaxed. A unique coexistence of rocksalt and spinel-HEO phases, which are fully coherent with no detectable chemical segregation, is revealed by transmission electron microscopy. This dual-phase coexistence appears as a universal phenomenon in (Co$_{0.2}$Cr$_{0.2}$Fe$_{0.2}$Mn$_{0.2}$Ni$_{0.2}$)$_{3}$O$_{4}$ epitaxial films. Prominent changes in the magnetic anisotropy and domain structure highlight the strain-induced bidirectional control of magnetic properties in HEOs. When the films are relaxed, their magnetization behavior is isotropic, similar to that of bulk materials. However, under tensile strain, the hardness of the out-of-plane (OOP) axis increases significantly. On the other hand, compressive straining results in an easy OOP magnetization and a maze-like magnetic domain structure, indicating the perpendicular magnetic anisotropy. Generally, this study emphasizes the adaptability of the high entropy design strategy, which, when combined with coherent strain engineering, opens additional prospects for fine-tuning properties in oxides

Magnetic and magnetotransport properties of Fe-based glass-covered microwires

Magnetic and magnetotransport properties of glass-covered amorphous microwires of nominal composition Fe89B1Si3C3Mn4 have been studied. Samples of two families with the same composition but different metallic core diameters were annealed in a furnace or by Joule heating. The electrical resistance was measured as a function of time during annealing to study the effects on the samples' microstructures (evolution from the amorphous to the crystalline phase). Static hysteresis loops were measured on all samples by means of a vibrating sample magnetometer. Giant magneto-impedance measurements (GMI) performed on a coaxial line using a vectorial network analyser at frequencies up to 6 GHz showed that furnace-annealed samples display larger anisotropies with respect to Joule-heated ones; however, Joule heating is more effective in improving the magneto-impedance response of the alloy. The, maximum GMI ratio is ≈ 175% at 4 GHz. The influence of the different metallic core/total wire diameter on the induced anisotropies has been studied for the two families of samples through hysteresis loops and high-frequency GMI