Grigory Yu. Melnikov

Gadolinium is a rare-earth element that is promising for the field of biomedicine due to its unique properties that enhance image quality, giving it high potential in targeted cancer therapy, antimicrobial treatments, etc. The disadvantage of Gd-containing materials is their high toxicity. In this work, ensembles of Fe and Al₂O₃ nanoparticles were fabricated by the electric explosion of wire and Gd ribbons using rapid quenching techniques. Stable Fe, Fe/Gd and Fe/Gd/Al₂O₃ aqueous suspensions with a Z-potential of about −54 mV were fabricated by the ball-milling mechanosynthesis of Fe (100%), Fe and Gd (70 and 30 wt. % accordingly) and Fe, Al₂O_3, and Gd (69, 30 and 1 wt.% accordingly). Fillers from suspensions were used for the synthesis of epoxy composites mimicking natural tissue with embedded magnetic particles. The concentration range for synthesized epoxy composites (0, 5, 10, and 15 wt.% of the filler) corresponded to the biomedical range of interest. Thin-film magnetoimpedance (MI) elements were prepared by a sputtering technique: conventional [FeNi/Cu]₅/Cu/[Cu/FeNi]₅ (NP) element and [FeNi/Cu]₅/Cu/[Cu/P{FeNi]₅} element with patterned top multilayer (SqP). They showed a maximum MI ratio of about 160% for NP and about 60% for SqP. MI sensor response was affected by the presence of filled magnetic composites in the shape of cylinders (5 mm × 4 mm) situated at about 1 mm due to the stray fields in the filler. MI response showed a linear dependence on the filler concentration for each selected position. These results open the possibility to develop new iron- and gadolinium-containing materials for simultaneous magnetic imaging and detection by magnetic field sensors, extending the functional properties of Fe/Gd materials for biomedical devices and therapies.

Spherical magnetic nanoparticles consisting of an iron core and iron oxide shell (α-Fe/FeO_X) were fabricated by the electric explosion of the wire technique (EEW). The structure and magnetic properties of synthesized nanoparticles were experimentally investigated. Magnetic properties of an iron nanoparticle ensemble for individual defect-free, non-interacting iron-based nanoparticles having different diameters were calculated using micromagnetic modeling. Experimental and calculated magnetic hysteresis loops were comparatively analyzed.

Multilayered [Cu(3 nm)/FeNi(100 nm)]₅/Cu(150 nm)/FeNi(10 nm)/Cu(150 nm)/FeNi(10 nm)/Cu(150 nm)/[Cu(3 nm)/FeNi(100 nm)]₅ structures were obtained by using the magnetron sputtering technique in the external in-plane magnetic field. From these, multilayer magnetoimpedance elements were fabricated in the shape of elongated stripes using the lift-off lithographic process. In order to obtain maximum magnetoimpedance (MI) sensitivity with respect to the external magnetic field, the short side of the rectangular element was oriented along the direction of the technological magnetic field applied during the multilayered structure deposition. MI sensitivity was defined as the change of the total impedance or its real part per unit of the magnetic field. The design of the elements (multilayered structure, shape of the element, etc.) contributed to the dynamic and static magnetic properties. The magnetostatic properties of the MI elements, including analysis of the magnetic domain structure, indicated the crucial importance of magnetostatic interactions between FeNi magnetic layers in the analyzed [Cu(3 nm)/FeNi(100 nm)]₅ multilayers. In addition, the uniformity of the magnetic parameters was defined by the advanced technique of the local measurements of the ferromagnetic resonance field. Dynamic methods allowed investigation of the elements at different thicknesses by varying the frequency of the electromagnetic excitation. The maximum sensitivity of 40%/Oe with respect to the applied field in the range of the fields of 3 Oe to 5 Oe is promising for different applications.

Longitudinal giant magnetoimpedance effect of [Fe₂₁Ni₇₉/Cu]₅/Cu/[Fe₂₁Ni₇₉/Cu]₅ film element was investigated depends on stray magnetic field of epoxy magnetic composite with 30% weight concentration of iron oxide magnetic microparticles. Configuration of an experiment was a model of thrombus detection in a blood vessel. Stray magnetic field was varied by movement of a magnetic composite above the element perpendicular to the long side. Composite was either magnetized or not to the state of remanence. As the magnetic composite approaches the GMI element, MI ratio curves are smoothed and shifted along the field axis and maximum value of the MI ratio decreases. Magnetic properties of magnetic composite and film element were investigated as well.

The rectangular elements in magnetoimpedance (MI) configuration with a specific nanocomposite laminated structure based on FeNi and Cu layers were prepared by lift-off lithographic process. The properties of such elements are controlled by their shape, the anisotropy induced during the deposition, and by effects associated with the composite structure. The characterizations of static and dynamic properties, including MI measurements, show that these elements are promising for sensor applications. We have shown that competition between the shape anisotropy and the in-plane induced anisotropy of the element material is worth taking into account in order to understand the magnetic behavior of multilayered rectangular stripes. A possibility of the dynamic methods (ferromagnetic and spin-wave resonance) to describe laminated planar elements having a non-periodic modulation of both structure and magnetic parameters of a system is demonstrated. We show that the multilayered structure, which was originally designed to prevent the development of a “transcritical” state in magnetic layers and to reach the required thickness, also induces the effects that hinder the achievement of the goal, namely an increase in the perpendicular magnetic anisotropy energy.

The peculiarities of structure and static magnetic properties of composites based on epoxy resins with microparticles of iron oxide FeO_x, which are used as model materials for magnetic detection, have been investigated. The [FeNi/Cu]₅/[Cu/[Cu/FeNi]₅ film element with transverse magnetic anisotropy is used as a sensing element of the prototype of detector of weak magnetic fields operating on the basis of the magnetoimpedance (MI) effect. It is shown that there is a linear dependence of the specific magnetization on the concentration of microparticles in the range of 0–70 wt % despite notable differences in the structure of composites. Using the MI prototype of the weak field detector, a linear dependence of the change of the MI effect on the concentration of FeO_x microparticles in the frequency range of 80–260 MHz is found. It is shown that the esigned composites and film elements based on permalloy are complementary in terms of their functional properties and can be used as a model pair for magnetic detection.

The biological activity of γ-Fe₂O₃ magnetic nanoparticles (MNPs), obtained by the laser target evaporation technique, was studied, with a focus on their possible use in biosensor applications. The biological effect of the MNPs was investigated in vitro on the primary cultures of human dermal fibroblasts. The effects of the MNPs contained in culture medium or MNPs already uptaken by cells were evaluated for the cases of the fibroblast’s proliferation and secretion of cytokines and collagen. For the tests related to the contribution of the constant magnetic field to the biological activity of MNPs, a magnetic system for the creation of the external magnetic field (having no commercial analogues) was designed, calibrated, and used. It was adapted to the size of standard 24-well cell culture plates. At low concentrations of MNPs, uptake by fibroblasts had stimulated their proliferation. Extracellular MNPs stimulated the release of pro-inflammatory cytokines (Interleukin-6 (IL-6) and Interleukin-8 (IL-8) or chemokine (C-X-C motif) ligand 8 (CXCL8)) in a concentration-dependent manner. However, the presence of MNPs did not increase the collagen secretion. The exposure to the uniform constant magnetic field (H ≈ 630 or 320 Oe), oriented in the plane of the well, did not cause considerable changes in fibroblasts proliferation and secretion, regardless of presence of MNPs. Statistically significant differences were detected only in the levels of IL-8/CXCL8 release.

The development of magnetoactive microsystems for targeted drug delivery, magnetic biodetection, and replacement therapy is an important task of present day biomedical research. In this work, we experimentally studied the mechanical force acting in cylindrical ferrogel samples due to the application of a non-uniform magnetic field. A commercial microsystem is not available for this type of experimental study. Therefore, the original experimental setup for measuring the mechanical force on ferrogel in a non-uniform magnetic field was designed, calibrated, and tested. An external magnetic field was provided by an electromagnet. The maximum intensity at the surface of the electromagnet was 39.8 kA/m and it linearly decreased within 10 mm distance from the magnet. The Ferrogel samples were based on a double networking polymeric structure which included a chemical network of polyacrylamide and a physical network of natural polysaccharide guar. Magnetite particles, 0.25 micron in diameter, were embedded in the hydrogel structure, up to 24% by weight. The forces of attraction between an electromagnet and cylindrical ferrogel samples, 9 mm in height and 13 mm in diameter, increased with field intensity and the concentration of magnetic particles, and varied within 0.1–30 mN. The model provided a fair evaluation of the mechanical forces that emerged in ferrogel samples placed in a non-uniform magnetic field and proved to be useful for predicting the deformation of ferrogels in practical bioengineering applications.

Thin FeNi films 100 nm in thickness and arrays of periodic square microelements (50, 70, and 300 µm in size of individual microelements) located in the same plane have been developed, synthesized, and experimentally studied. The structure, static magnetic properties, and ferromagnetic resonance features of film arrays created by ion-plasma sputtering with the use of masks have been comparatively analyzed. It is implied that a similar magnetic structure could be incorporated into multilayer sensor elements with a high giant magnetoimpedance to increase their sensitivity to magnetic field.