In this work, solid-phase hydrogen diffusion is investigated as a treatment for a Co-based (Co75.4Fe3.5Cr3.3Si17.8) amorphous membrane, made of metallic glass. We report a noticeable growth of diffusion through the amorphous membrane at higher environmental acidity and constant ionic activity in the chloride-acidic solutions. This effect has been explained by a presence of two adsorpted hydrogen atomic forms (superficial and subsurface ones) on the specimen surface during the chemical treatment. Mentioned impact provides explicit changing by magnetic and mechanical properties of the alloy, and it is compared and approved using literature data. A scheme of the process has been proposed and verified with X-ray photoelectron spectroscopy and magnetometry. Presented results can be interesting both from fundamental and practical standpoints in material science and technology of amorphous alloys.

Two-layered structures consisting of piezopolymer and magnetic elastomer were investigated as magnetoelectric material. Three types of magnetic elastomer based on cobalt ferrite (CoFe2O4) and Ni- or Zn-substituted CoFe2O4 nanoparticles were used as magnetically sensitive layers. Cobalt ferrite nanoparticles are considered one of the most promising metal-oxide nanomaterials because of their favorable magnetic properties, such as high saturation magnetization and magnetic anisotropy. The substitution of Co2+ in cobalt ferrite with other transition metals allows for additional tailoring of these properties. The modified magnetic behavior of the substituted CoFe2O4 nanoparticles directly influenced the magnetic properties of magnetic elastomers and, consequently, the magnetoelectric response of composite structures. In this case, the resonant frequency of the magnetoelectric effect remained largely independent of the type of magnetic nanoparticles in the magnetic elastomer layer but its magnitude increased upon Zn substitution up to ~107 mV·cm-1·Oe-1. These findings highlight the potential of chemically engineered magnetic properties of CoFe2O4 nanoparticles for manufacturing magnetoelectric composites to expand their applications in energy harvesting and sensors.

The hybrid hydrogels were synthesized composed of hyaluronate/polyacrylate mixture cross-linked by magnetic gamma-Fe2O3 nanoparticles. Incorporation of short polyacrylate chains into the hydrogels increases the size of gamma-Fe2O3 nanoparticles thus enhancing the magnetic hydrogel properties. The hydrolytic enzyme initiates degradation of the hybrid hydrogels down to smaller particles, which persist in solution due to complexation with polyacrylate chains. The results are of interest for preparing magnetically controlled biodegradable polymer carriers for encapsulation of bioactive substances.

FeRh-based alloys are unique objects, the study of which allows us to identify new features of first-order magnetic phase transitions. Doping of an alloy often leads to significant changes in its magnetic properties. This paper examines the structural, magnetic, transport and caloric properties of iron-rhodium alloys with different cobalt doping with varying cobalt content (0-1.8 at%). Doping the alloy with less than 2 at% cobalt resulted in a decrease in the phase transition temperature by 200 K. Based on the results obtained, a relationship was established between the magnetic properties and the heterogeneity of the elemental composition of the samples. It was also demonstrated that significant changes in the parameters of the magnetic phase transition of the alloy upon alloying are largely determined by the electronic properties. Considering the sensitivity of the alloy properties to the cobalt content, we develop a novel methodology for quantifying local compositional variations using temperature-dependent measurements, demonstrating its superior sensitivity compared to conventional techniques. The strong correlation between magnetocaloric response and cobalt concentration highlights the importance of precise composition control for applications.

Mass production of biomedical microrobots demands expensive and complex preparation techniques and versatile biocompatible materials. Learning from natural bacteria flagella, the study demonstrates a magnetic polymer multilayer cylindrical microrobot that bestows the controllable propulsion upon an external rotating magnetic field with uniform intensity. The magnetic microrobots are constructed by template-assisted layer-by-layer technique and subsequent functionalization of magnetic particles onto the large opening of the microrobots. Geometric variables of the polymer microrobots, such as the diameter and wall thickness, can be controlled by selection of porous template and layers of assembly. The microrobots perform controllable propulsion through the manipulation of magnetic field. The comparative analysis of the movement behavior reveals that the deformation of microrobots may be attributed to the propulsion upon rotating magnetic field, which is similar to that of natural bacteria. The influence of actuation and frequency on the velocity of the microrobots is studied. Such polymer multilayer magnetic microrobots may provide a novel concept to develop rapidly delivering drug therapeutic agents for diverse practical biomedical uses.

Abstract—The effect of severe plastic deformation performed in a Bridgman anvils at 77 K on the saturation magnetization, the phase composition, and the crystal geometry characteristics of the phases of a metastable austenitic–martensitic Fe–18Cr–10Ni alloy is investigated. High-pressure (hydrostatic) torsion at a true strain e = 3.4–5.8 at 77 K is found to form two martensitic phases, namely, the ferromagnetic α phase and the paramagnetic ε phase. Mechanisms explaining the nature of changing the saturation magnetization are proposed.

Co 0.3 Zn 0.7-x Ni x Fe 2 O 4 (0 <= x <= 0.7) spinel ferrites were produced by the solid-state reaction method. It was shown that all samples can be characterized by the single-phase state (space group Fd-3 m). The behavior of the lattice parameters and the volume of the unit cell correlate well with the average of the ionic radii of the Zn 2 + and Ni 2 + and their concentration in Co 0.3 Zn 0.7-x Ni x Fe 2 O 4 (0 <= x <= 0.7). The dependence of the hyperfine parameters of the Mo ssbauer spectra at two temperatures on the nickel content was studied. It was demonstrated that increase of the Ni content leads to the increase of the remnant magnetization and coercivity. It can be explained by the increase of the magnetic domain volume. It was concluded that electronic configuration of the Zn and Ni ions and their concentration in Co 0.3 Zn 0.7-x Ni x Fe 2 O 4 (0 <= x <= 0.7) not so critically impact on magnetic properties as well as the features of the cation distribution in oxygen coordination and the peculiarities of the intra- and interlattice exchange interactions.

The surface of an amorphous cobalt-based alloy with a nominal composition of Co75Si15Fe5Cr4.5Al0.5 was modified with nanostructures by anodizing in an ionic liquid—1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. The magnetic (specific saturation magnetization and coercive force) and corrosion (corrosion potential and resistance) characteristics of an amorphous alloy before and after electrochemical modification of the surface with nanostructures have been compared. Modification of the alloy surface partially changes its magnetic properties. After corrosion tests, an increase in the coercive force is observed. Corrosion tests were carried out using the polarization curve method in Ringer’s solution. The corrosion resistance of alloys modified with oxide nanostructures is higher than the corrosion resistance of an abrasive-treated alloy. The increase in corrosion resistance is determined mainly by the presence of nanostructures.

The search for novel materials with enhanced characteristics for the advancement of flexible electronic devices and energy harvesting devices is currently a significant concern. Multiferroics are a prominent example of energy conversion materials. The magnetoelectric conversion in a flexible composite based on a piezopolymer layer and a magnetic elastomer layer was investigated. The study focused on investigating the dynamic magnetoelectric effect in various configurations of external alternating and constant homogeneous magnetic fields (L-T and T-T configurations). The T-T geometry exhibited a two orders of magnitude higher coefficient of the magnetoelectric effect compared to the L-T geometry. Mechanisms of structure bending in both geometries were proposed and discussed. A theory was put forward to explain the change in the resonance frequency in a uniform external field. A giant value of frequency tuning in a magnetic field of up to 362% was demonstrated; one of the highest values of the magnetoelectric effect yet recorded in polymer multiferroics was observed, reaching up to 134.3 V/(Oe∙cm).

In recent years, more and more attention has been paid to the study of various amorphous materials. This is due to the fact that these materials have unique sets and combinations of properties, which is why they are widely used in microelectronics, instrumentation, and medicine. The present work is aimed to study the characteristics of the magnetic response of microspirals made of an amorphous magnetic alloy.

The work is dedicated to the study of the magnetic response of a metasurface made of split ring resonators (meta-atoms) in the MHz and GHz ranges. A new method for calculating the local permeability of a metasurface in the MHz frequency range is proposed, taking into account the finite sizes of the elements, and for the first time, a result of high degree of accuracy matching with experimental values has been obtained. In the GHz range, additional factors such as the retardation effect, nonuniform current distribution in the meta-atom, and the complexity of the nature of meta-atoms’ interaction compared to the MHz range are also considered, in particular, the emergence of electrical interaction between them.

The possibility of synthesizing nanoparticles by pulsed laser ablation of thin cobalt films in water is shown. The average size of the formed nanoparticles varies in the range of 70–1020 nm depending on the thickness of the ablated film. At film thicknesses less than 35 nm, the size dispersion of the nanoparticles is minimum. The produced nanoparticles are characterized by magnetic response and structurally most closely correspond to cobalt oxide Co3O4.

The effect of giant magnetoimpedance in magnetic structure with inhomogeneous electric current distribution is studied. A special design reduces the magnitude of the intrinsic magnetic field outside the structure. The magnetoimpedance of such a planar structure made of magnetically soft material with radial current distribution has been investigated both theoretically and experimentally. The theoretical evaluations show a strong variation of the impedance of the structure with the frequency and the permeability value of the material. The results of calculations are qualitatively confirmed by experimental data for model samples.

Reducing the size of a material with a first-order magnetic phase transition to the nanoscale results in a significant change in its physical properties. An example of this behaviour is the FeRh alloy. According to magnetometry results, the nanoparticles of this alloy do not show a transition from the antiferromagnetic to the ferromagnetic state near room temperature. In this work we have measured the magnetic properties and the Mo center dot ssbauer effect for FeRh@FeO composite nanoparticles at different temperatures. An analysis of the results allows us to conclude that superparamagnetic relaxations dominate the formation of the magnetic structure of the nanoparticles. For particle sizes near 10 nm, the antiferromagnetic state is possible near helium temperatures. Further heating contributes to the formation of superparamagnetic behaviour.

Magnetoelectric (ME) effects in composite heterostructures containing mechanically coupled ferromagnetic and piezoelectric layers enable the mutual transformation of magnetic and electric fields and form the basis for the development of magnetic field sensors, actuators and energy harvesters. Promising materials for such composite structures are magnetoactive elastomers (MAE), which are silicone matrices with ferromagnetic particles uniformly distributed within them. The strong dependence of MAE properties on magnetic fields and their low rigidity enable contactless control of ME effects characteristics within such structures. In this work we have experimentally investigated the dynamics of resonant ME effects in a structure consisting of a MAE layer with carbonyl iron particles and a layer of polyvinylidene fluoride piezopolymer in a cantilever geometry. For the structure magnetized in a plane along the axis, the frequency tuning of the bending oscillations reached 360 % at the fields up to 2 kOe, and the maximum ME conversion coefficient was 1.74 V/(Oe center dot cm). For the structure magnetized perpendicular to the plane, an orientation transition was observed, which manifested itself as a jump-like bending of the structure to the angle up to similar to 85 degrees at magnetic field above the critical value. The frequency tuning by the magnetic field reached 185 %, and the maximum ME conversion coefficient was 135 V/(Oe center dot cm). A model has been developed that qualitatively describes the dynamics of ME effect in composite cantilever structures with a MAE layer for different orientations of the applied magnetic field.

Cobalt-based Amorphous Metal Alloys (AMA) can be used as soft magnetic materials in various magnetic devices due to the low value of the natural crystalline magnetic anisotropy. The addition of non-metallic components (Si, B) does not adversely affect the magnetic properties. On the contrary, AMA have high magnetic permeability at low values of coercive force and greater resistance to corrosion compared to crystalline ones. The required important parameters for corrosion description are: the concentration of chloride-ions, the microstructure (especially surface heterogeneity) and the composition of the oxide layer [1]. It was determined that the initial AMA Co75Si15Fe5Cr4.5Al0.5 possesses the low coercive force 0.38 A/m. The modification of the alloy surface with nanostructures by anodizing at different current densities (i) and times in the BmimBF 4 ionic liquid (IL) does not affect the value of the coercive force, but its resistance to corrosion in a chloride solution increases. The coercive force increases after corrosion, which may be due to a change in surface morphology. The domain structures of the surface modified with nanostructures and initial alloys are different. After excerption at a constant (i) in IL, the domain structure of the surface consists of relatively large uniformly magnetized regions (Fig. 1a). The coercive force of the sample practically does not change compared to the initial sample. The surface domains after corrosion are broken into smaller ones, while the predominant orientation changes its direction (Fig.1 b). The change in the surface domain structure is accompanied by a significant increase in the coercive force (by a factor of 10), although the maximum magnetic permeability (the slope of the hysteresis loops) does not change. The EIS-tests (electrical impedance spectroscopy) were performed at -200 mV (Ag/AgCl) in the frequency range of 50,000 to 0.01 Hz and an oscillation amplitude of 20 mA in Ringer's solution (Fig.1 c, d) to compare the charge transfer kinetics for modified with nanostructures and initial samples. The simulated equivalent circuit included the values of the solution resistance Rs (22 Ω), the value of the constant phase element CPE associated with the double layer capacity, including the capacitance of the modified surface layer, and Rp is the charge transfer resistance across the interface. The capacity of the double layer is higher for the modified sample (4.28*10 -5 Ohm -1 *c N vs. 1.88*10 -5 Ом -1 *с N ) and the resistance value of the material has hardly changed (18000±13.5% Ohm for modified and 15500±3.5% Ohm for unmodified). The values of the phase angle (0.78 - modified and 0.88 - unmodified) indicate a greater heterogeneity of the charge distribution at the boundaries of the double layer for the modified surface of the alloy. So, surface modification affects the corrosion resistance, while it has little effect on the parameters of hysteresis loops, what is very important in practical applications. Nyby, C., Guo, X., Saal, J. E., Chien, S.-C., Gerard, A. Y., Ke, H., Frankel, G. S. (2021). Electrochemical metrics for corrosion resistant alloys. Scientific Data, 8(1). doi:10.1038/s41597-021-00840-y Figure 1

In this work, an attempt was made to reveal and explain the influence of the process of formation of 2D nanostructures at the surface of an amorphous alloy (an alloy with the composition Co75Si15Fe5Cr4.5Al0.5 (in at.%) was used for this purpose) on the corrosion and magnetic properties of such an alloy. Two-dimensional nanostructures (nanocells of 100–150 nm in size, which were obtained by anodizing the initial sample in an ionic liquid) are essentially a pattern on the surface of the sample, and they cannot completely cover and block the surface from external effects. It was postulated that the presence of these nanostructures during corrosion and magnetic tests has no significant effect. However, a noticeable inhibition effect was observed during corrosion tests and a less noticeable (but still detectable) effect was observed during magnetic tests. The authors believe that the effect obtained, with a detailed study, can be used to increase the corrosion resistance and to improve the properties of traditional magnetic materials.

Magnetic and magnetothermal properties of annealed Zn0.2Mn0.8Fe2O4 nanoparticles with diameter value, ranging from 9 to 35 nm, have been investigated and compared with earlier investigated unannealed Zn0.2Mn0.8Fe2O4 magnetic nanoparticles (MNPs). A single-phase spinel structure was observed in both types of MNPs. It has been demonstrated that for the large annealed Zn0.2Mn0.8Fe2O4 nanoparticles (24.7, 31.4, 35.1 nm) the value of specific absorption rate (SAR) is proportional to the amplitude of the magnetic field as ∼H4. However, for earlier investigated unannealed Zn0.2Mn0.8Fe2O4 MNPs, superquadratic dependence SAR ∼H5 have been found starting from 13 nm. Significant change of dependence of the character of SAR(d) may be explained by low values of hysteresis area of small annealed MNPs and, thus, dominant role of Néel relaxation in these annealed Zn0.2Mn0.8Fe2O4 nanoparticles.

Multilayered magnetoelectric materials are of great interest for investigations due to their unique tuneable properties and giant values of magnetoelectric effect. The flexible layered structures consisting of soft components can reveal lower values of the resonant frequency for the dynamic magnetoelectric effect appearing in bending deformation mode. The double-layered structure based on the piezoelectric polymer polyvinylidene fluoride and a magnetoactive elastomer (MAE) with carbonyl iron particles in a cantilever configuration was investigated in this work. The gradient AC magnetic field was applied to the structure, causing the bending of the sample due to the attraction acting on the magnetic component. The resonant enhancement of the magnetoelectric effect was observed. The main resonant frequency for the samples depended on the MAE properties, namely, their thickness and concentration of iron particles, and was 156–163 Hz for a 0.3 mm MAE layer and 50–72 Hz for a 3 mm MAE layer; the resonant frequency depended on bias DC magnetic field as well. The results obtained can extend the application area of these devices for energy harvesting.