Abstract P-7: NdFeCo-based Nanoparticles for Biomedical Applications

Background: The multifunctional nanoparticles can be promising antitumor materials. The results of a study of synthesized NdFeCoB oxide nanoparticles (NPs) as a basis for drug transportation systems are presented. In the next step, the NPs can be coated by a multifunctional gel shell. Methods: NPs, the composition of NdFexCo1-xB (where x =0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5), were synthesized by a Pechini-type sol-gel method. The synthesis allows tuning of NPs magnet properties by manipulating the microstructure and phase composition. NPs were studied by XRD, SEM, TEM, HRTEM, and VSM. Results: SEM images show that the average size of NPs changed from 280 nm (for x = 0) up to 416 nm (for x = 0.1 – 0.5). At TEM images the NPs of the sample without cobalt (x = 0) have an elongated shape (Fig 1a). Diffraction patterns showed that the NPs consist of single crystal or ordered crystallites. NPs with cobalt mainly consist of crystallites with a size of about 20-50 nm. There are also areas with a complex-grained microstructure. Hysteresis loops and first-order reversal curve analysis indicated that the NPs were ferromagnetic whose coercivity, squareness ratio, and magnetic interactions changed significantly with the cobalt contents

Analyzer-free, intensity-based, wide-field magneto-optical microscopy

In conventional Kerr and Faraday microscopy, the sample is illuminated with plane-polarized light, and a magnetic domain contrast is generated by an analyzer making use of the Kerr or Faraday rotation. Here, we demonstrate possibilities of analyzer-free magneto-optical microscopy based on magnetization-dependent intensity modulations of the light. (i) The transverse Kerr effect can be applied for in-plane magnetized material, as demonstrated for an FeSi sheet. (ii) Illuminating that sample with circularly polarized light leads to a domain contrast with a different symmetry from the conventional Kerr contrast. (iii) Circular polarization can also be used for perpendicularly magnetized material, as demonstrated for garnet and ultrathin CoFeB films. (iv) Plane-polarized light at a specific angle can be employed for both in-plane and perpendicular media. (v) Perpendicular light incidence leads to a domain contrast on in-plane materials that is quadratic in the magnetization and to a domain boundary contrast. (vi) Domain contrast can even be obtained without a polarizer. In cases (ii) and (iii), the contrast is generated by magnetic circular dichroism (i.e., differential absorption of left- and right-circularly polarized light induced by magnetization components along the direction of light propagation), while magnetic linear dichroism (differential absorption of linearly polarized light induced by magnetization components transverse to propagation) is responsible for the contrast in case (v). The domain-boundary contrast is due to the magneto-optical gradient effect. A domain-boundary contrast can also arise by interference of phase-shifted magneto-optical amplitudes. An explanation of these contrast phenomena is provided in terms of Maxwell-Fresnel theory. © 2021 Author(s)

Abstract P-8:Fe2O3-SiO2-Au Core-Shell Nanoparticles for Theranostics

Background: Core-shell nanoparticles (NPs) Fe3O4-SiO2 covered with Au grains due to their unique magnetic, biological, optical and mechanical properties are promising nanostructured material especially in biomedical field. Magnetic core allows controlling the position of NPs, SiO2 shell makes them biocompatible and decrease magnetostatic interactions between them, and Au NPs on the surface allow creating additional matrix around them and using such systems as controlled nanocontainers in tasks of drug delivery, magnetic resonance imaging and target cancer cell therapy. Methods: Inner magnetic core of the NPs was synthesized using polyol method, a 3-step process which resulting in magnetite NPs with hydrophilic surface. Shell was made by covering Fe3O4 particles in surfactant and growing SiO2 on top of them by sol-gel method. Covering core-shell NPs with 3.5 nm Au seed grains using monosilane and their further growth to control diameter. Structural properties were studied using TEM and Dual Beam SEM. Magnetic properties were investigated using LakeShore VSM 7400 magnetometer. Results: Two samples with different concentration of Au NPs were investigated. SEM observations show that core-shell Fe3O4-SiO2 are spherical with average diameter of 200 nm and Au NPs with diameter of 15 nm are evenly dispersed on their surface. Magnetic measurements showed that different concentration of Au NPs results in different coercive forces of the sample. Decreasing the temperature to 77 K showed up to 6 times increase of coercive force and slight increase in magnetization. Conclusion: Biocompatible magnetic nanoparticles are critical advances in biomedical applications. In this work, we studied the morphology of the samples, demonstrated the change of coercive force of NPs with different Au concentration and investigated their magnetic properties in low temperatures

Noise-controlled signal transmission in a multithread semiconductor neuron

We report on stochastic effects in a new class of semiconductor structures that accurately imitate the electrical activity of biological neurons. In these devices, electrons and holes play the role of K+ and Na+ ions that give the action potentials in real neurons. The structure propagates and delays electrical pulses via a web of spatially distributed transmission lines. We study the transmission of a periodic signal through a noisy semiconductor neuron. Using experimental data and a theoretical model we demonstrate that depending on the noise level and the amplitude of the useful signal, transmission is enhanced by a variety of nonlinear phenomena, such as stochastic resonance, coherence resonance, and stochastic synchronization

Photovoltage spectroscopy of dipolar spin waves in Dy micromagnets

We report on a sensitive spectroscopic technique for probing the spin excitations of individual submicron magnets. This technique uses a high mobility two dimensional electron gas (2DEG) confined in a GaAs/AlGaAs heterojunction to pick up the oscillating dipolar magnetic field emanating from the individual spin wave modes of micromagnets fabricated at its surface. We review a range of dynamic phenomena that demonstrate the formation of magnetostatic waves in finger gate arrays, dipolar edge spin waves in bar magnets, vortex hysteresis in magnetic dots and the photovoltage dependence on microwave polarization.</jats:p

Field-free spin-orbit torque switching enabled by interlayer Dzyaloshinskii-Moriya interaction

Perpendicularly magnetized structures that are switchable using a spin current under field-free conditions can potentially be applied in spin-orbit torque magnetic random-access memory(SOT-MRAM).Several structures have been developed;however,new structures with a simple stack structure and MRAM compatibility are urgently needed.Herein,a typical structure in a perpendicular spin-transfer torque MRAM,the Pt/Co multilayer and its synthetic antiferromagnetic counterpart with perpendicular magnetic anisotropy, was observed to possess an intrinsic interlayer chiral interaction between neighboring magnetic layers,namely the interlayer Dzyaloshinskii-Moriya interaction (DMI) effect. Furthermore, using a current parallel to the eigenvector of the interlayer DMI, we switched the perpendicular magnetization of both structures without a magnetic field, owing to the additional symmetry-breaking introduced by the interlayer DMI. This SOT switching scheme realized in the Pt/Co multilayer and its synthetic antiferromagnet structure may open a new avenue toward practical perpendicular SOT-MRAM and other SOT devices

Fabrication of high-resolution nanostructures of complex geometry by the single-spot nanolithography method

The paper presents a method for the high-resolution production of polymer nanopatterns with controllable geometrical parameters by means of a single-spot electron-beam lithography technique. The essence of the method entails the overexposure of a positive-tone resist, spin-coated onto a substrate where nanoscale spots are exposed to an electron beam with a dose greater than 0.1 pC per dot. A single-spot enables the fabrication of a nanoring, while a chain of spots placed at distance of 5–30 nm from each other allows the production of a polymer pattern of complex geometry of sub-10 nm resolution. We demonstrate that in addition to the naturally oxidized silicon substrates, gold-coated substrates can also successfully be used for the single-spot nanopattering technique. An explanation of the results related to the resist overexposure was demonstrated using Monte Carlo simulations. Our nanofabrication method significantly accelerates (up to 10 times) the fabrication rate as compared to conventional lithography on positive-tone resist. This technique can be potentially employed in the electronics industry for the production of nanoprinted lithography molds, etching masks, nanoelectronics, nanophotonics, NEMS and MEMS devices