The structural and magnetic properties of a niobium nitride (NbN) film prepared by reactive sputtering onto a quartz substrate are investigated. It is shown using scanning electron microscopy that the film has a columnar structure with a diameter of crystallite columns of about 50 nm. The film magnetization loops are measured for the field orientation parallel and perpendicular to its surface. Based on the experimental data, the critical current densities of the film are estimated in both cases. For the field parallel to the film surface, the estimate is 6.5 × 104 A/cm2 at the liquid helium temperature. For the field perpendicular to the surface, the critical current density is close to the depairing current density (107 A/cm2). Analysis of the results based on different models of magnetic vortex pinning in superconductors shows that in the former case, pinning occurs at the boundaries of columns in the bulk of the sample, while in the latter case, it is determined by the influence of the surface barrier.

Research is carried out on approaches for the digital adaptive platform for learning programming with the teamwork skills forming function application. The work environment interface and key components that make the platform adaptable are demonstrated. The platform services responsible for information security functions are detailed. An example of the presented task is given.

The results of a study conducted within the framework of an interactive approach to the task formation, which is an actual branch of computer methods in education, are presented. The author notes that the branch is currently not used for teaching information technologies practice in higher educational institutions due to the labor cost of forming, implementing and taking into account the impact of interactive tasks on the success of the educational process participants. The purpose of the study is to substantiate the introduction of relevant information technologies into the educational process, as well as approaches to the verification and formation of knowledge. It tested the main hypothesis: tasks aimed at interactive activity better help students in mastering the material, based on their own perception, than static tasks based on traditional approaches in the educational process with information technologies application. An intraindividual scheme of the experiment is used on the basis of traditional and interactive tasks, different types of tasks are presented to the same group of students. The sample for the participants of the experiment is recruited among the most capable students of the Information Technologies Faculty, bachelors, 2-4 year of experience according to the criterion of academic performance in the framework of specialized disciplines (28 people participated). The variables are empirically selected characteristics that reflect the useful qualities of the task in the context of the educational process. Methods of descriptive statistics are used to test hypotheses. It is noted that the results of the study make it possible to determine and formulate conditions that allow maximum use of the advantages of each of the studied types of tasks. The research confirms the demand for the development of teaching tools for students using interactive tasks, indicating the boundary conditions under which, according to the author, an interactive approach to the construction and implementation of tasks can demonstrate its effectiveness.

The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60-90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments gun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the gun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of -4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is -130 gB (gB is the Bohr magneton) per particle, which corresponds to 60-70 decompensated spins of nickel atoms localized, according to the Ne acute accent el hypothesis (gun -3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.

We report a study of the magnetodynamics of cobalt ferrite (CoFe 2 O 4 ) nanoparticles with an average diameter of ∼6 nm. Hysteresis loops were measured under quasi-static conditions and in pulse fields with amplitudes H 0 of up to 130 kOe and for durations τ P of 8 and 16 ms. The growth of coercivity H c observed with an increase in the magnetic field variation rate dH / dt (determined by the values of H 0 and τ P ) and the reduction of H c with temperature is ascribed to the superparamagnetic effect. The proposed theoretical model explains the observed dependences fairly well. Notably, the effective magnetic anisotropy constant obtained exceeds the value for bulk crystals and might be indicative of the contribution of surface magnetic anisotropy.

An alternative method for the synthesis of samples of high-temperature superconductors (HTSCs) is proposed, in which nanoscale superconducting layers should form on the surface of refractory granules of the “green phase” Ho2BaCuO5 immersed in the liquid phase BaCuO2 + CuO.

A study of existing approaches to creating educational environments for learning programming is conducted. Their main shortcomings are analyzed. The concept of a digital adaptive platform for learning programming, taking into account the identified shortcomings, is proposed. The features of the software implementation are described in a form of links between platform components, operation concepts and the platform architecture overall. The features of the software architecture and implementation of the digital adaptive platform for learning programming with the teamwork skills forming function are demonstrated.

An alternative technique for synthesizing high-temperature superconductor samples is proposed, in which superconducting layers should form on the surface of hard-melting Ho2BaCuO5 green phase grains immersed in the liquid phase BaCuO2 + CuO.

The Fe3O4/CoFe2O4 nanoparticles with a core–shell structure with an average size of 5 nm have been obtained by codeposition from the iron and cobalt chloride solutions. An analysis of the magnetic properties of the obtained system and their comparison with the data for single-phase Fe3O4 (4 nm) and CoFe2O4 (6 nm) nanoparticles has led to the conclusion about a noticeable interaction between the soft magnetic (Fe3O4) and hard magnetic (CoFe2O4) phases forming the core and shell of hybrid particles.

The magnetic structure of the polymorphic modification of iron oxide ε-Fe2O3 is collinear ferrimagnetic in the range from room temperature to ~ 150 K. Further, with decreasing a temperature in ε-Fe2O3, a magnetic transition occurs, accompanied by a significant decrease in the coercive force HC, and in the low temperature range ε-Fe2O3 is characterized by a complex incommensurate magnetic structure. In this work, we experimentally investigated the processes of dynamic magnetization reversal of ε-Fe2O3 nanoparticles of an average size of 8 nm in the temperature range of 80–300 K, comprising various types of magnetic structure of this iron oxide. A bulk material was studied - xerogel SiO2 with ε Fe2O3 nanoparticles embedded in pores. To measure the magnetic hysteresis loops under dynamic magnetization reversal, a pulsed magnetic field technique of Hmax up to 130 kOe was used, using the method of discharging a capacitor bank through a solenoid. The coercive force of HC during dynamic magnetization reversal noticeably exceeds HC for quasi-static conditions. This is caused by processes of superparamagnetic relaxation of the magnetic moments of particles during pulsed magnetization reversal. In the range from room temperature to ~ 150 K, the rate of change of the external field dH / dt is the main parameter determining the behavior of the coercive force under the conditions of dynamic magnetization reversal. This behavior is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K), when the magnetic structure of ε Fe2O3 is incommensurate, the coercive force during pulsed magnetization reversal already depends on the parameter dH / dt, and is largely determined by the maximum applied field Hmax. Such a behavior, atypical for systems of ferrimagnetic particles, is already caused by dynamic spin processes inside ε-Fe2O3 particles during fast magnetization reversal.

We report on the investigations of a system of 8-nm NiO particles representing antiferromagnetic (AFM) materials, which are weak magnetic in the form of submicron particles, but can be considered to be magnetoactive in the form of nanoparticles due to the formation of the uncompensated magnetic moment in them. The regularities of the behavior of magnetization switching in AFM nanoparticles are established by studying the magnetic hysteresis loops under standard quasi-static conditions and in a quasi-sinusoidal pulsed field of up to 130 kOe with pulse lengths of 4-16 ms. The magnetic hysteresis loops are characterized by the strong fields of the irreversible magnetization behavior, which is especially pronounced upon pulsed field-induced magnetization switching. Under the pulsed field-induced magnetization switching conditions, which are analogous to the dynamic magnetic hysteresis, the coercivity increases with an increase in the maximum applied field H-0 and a decrease in the pulse length. This behavior is explained by considering the flipping of magnetic moments of particles in an external ac magnetic field; however, in contrast to the case of single-domain ferro- and ferrimagnetic particles, the external field variation rate dH/dt is not a universal parameter uniquely determining the coercivity. At the dynamic magnetization switching in AFM nanoparticles, the H-0 value plays a much more important role. The results obtained are indicative of the complex dynamics of the interaction between magnetic subsystems formed in AFM nanoparticles.

The magnetic structure of the ε-Fe 2 O 3 iron oxide polymorphic modification is collinear ferrimagnetic in the range from room temperature to ~150 K. As the temperature decreases, ε-Fe 2 O 3 undergoes a magnetic transition accompanied by a significant decrease in the coercivity H c and, in the low-temperature range, the compound has a complex incommensurate magnetic structure. We experimentally investigated the dynamic magnetization switching of the ε-Fe 2 O 3 nanoparticles with an average size of 8 nm in the temperature range of 80–300 K, which covers different types of the magnetic structure of this iron oxide. A bulk material consisting of xerogel SiO 2 with the ε-Fe 2 O 3 nanoparticles embedded in its pores was examined. The magnetic hysteresis loops under dynamic magnetization switching were measured using pulsed magnetic fields H max of up to 130 kOe by discharging a capacitor bank through a solenoid. The coercivity Н с upon the dynamic magnetization switching noticeably exceeds the Н с value under the quasi-static conditions. This is caused by the superparamagnetic relaxation of magnetic moments of particles upon the pulsed magnetization switching. In the range from room temperature to ~ 150 K, the external field variation rate dH / dt is the main parameter that determines the behavior of the coercivity under the dynamic magnetization switching. It is the behavior that is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K) when the ε-Fe 2 O 3 magnetic structure is incommensurate, the coercivity during the pulsed magnetization switching depends already on the parameter dH / dt and is determined, to a great extent, by the maximum applied field H max . Such a behavior atypical of systems of ferrimagnetic particles is caused already by the dynamic spin processes inside the ε-Fe 2 O 3 particles during fast magnetization switching.

The structural, thermal, static magnetic, and resonance properties of the low-dimensional NaCuFe2(VO4)3 compound obtained by the solid-phase synthesis have been investigated. In the temperature range of 110–300 K, the electron spin resonance in the X band with a g factor of 2.008 has been detected. The magnetic properties of a sample with a high frustration level in the paramagnetic, antiferromagnetic, and disordered states have been examined. A shift of the Néel temperature to the high-temperature region in an external magnetic field has been observed. The origin of the disordered magnetism in NaCuFe2(VO4)3 are discussed. The features of substitution of sodium for lithium on the physical properties of the ACuFe2(VO4)3 (A = Na, Li) system have been established. It is shown that the chemical pressure changes the crystal lattice parameters, spacings between magnetic ions, and crystallite size, which is reflected in the physical properties of the material.

The results of the study of structural, thermal, static magnetic and resonance properties of the low-dimensional compound NaCuFe2(VO4)3 prepared by the standard solid-phase reaction method are presented. In the temperature range 110–300 K and in the X-band, an electron paramagnetic resonance was observed, characterized by a g-factor equal to 2.008. The magnetic properties of the sample with a high level of frustrations in the paramagnetic, antiferromagnetic, and disordered states are investigated. A shift of the Néel temperature to high temperatures under the influence of an external magnetic field was detected. The reasons for the appearance of disordered magnetism in NaCuFe2 (VO4) 3 are discussed. The features of the effect of sodium substitution by lithium on the physical properties of the ACuFe2 (VO4) 3 (A = Na, Li) system are revealed. It is shown that under the influence of chemical pressure there is a transformation of lattice parameters, distances between magnetic ions, crystallite size, which leads to a change in physical properties.

The Fe 3 O 4 /CoFe 2 O 4 nanoparticles with a core–shell structure with an average size of 5 nm have been obtained by codeposition from the iron and cobalt chloride solutions. An analysis of the magnetic properties of the obtained system and their comparison with the data for single-phase Fe 3 O 4 (4 nm) and CoFe 2 O 4 (6 nm) nanoparticles has led to the conclusion about a noticeable interaction between the soft magnetic (Fe 3 O 4 ) and hard magnetic (CoFe 2 O 4 ) phases forming the core and shell of hybrid particles.

Fe3O4 / CoFe2O4 nanoparticles with a core-shell structure with an average size of 5 nm were obtained by co-precipitation from solutions of iron and cobalt chlorides. An analysis of the magnetic properties of the resulting system and their comparison with the data for single-phase Fe3O4 (4 nm) and CoFe2O4 (6 nm) nanoparticles led to the conclusion that there is a noticeable interaction between the soft magnetic (Fe3O4) and magnetically hard (CoFe2O4) phases that form the core and the shell of hybrid particles, correspondingly.

Abstract In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe_2O_4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force H _C at the dynamic magnetization switching is markedly higher than H _C at quasi-static conditions. H _C increases as the pulse duration τ_ P decreases and the maximum applied field H _0 increases. The dependence of H _C on field variation rate dH / dt = H _0/2τ_ P is a unambiguous function for CoFe_2O_4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH / dt , and the value of applied field H _0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.

The dynamic magnetization switching of antiferromagnetic nickel oxide nanoparticles with a characteristic size of 8 nm has been experimentally investigated by pulsed field magnetometry. It is shown that, due to the presence of defects in NiO nanoparticles, as in other antiferromagnetic particles, the uncompensated magnetic moment is induced by the incomplete compensation of spins at the antiferromagnetic ordering. The dynamic magnetic hysteresis loops have been studied in pulsed fields with the maximum field (\(H_{{\max }}\)) of up to 130 kOe and pulse lengths (τP) of 4, 8, and 16 ms. According to the results obtained, the coercivity (HC) depends on both the τP and \(H_{{\max }}\) values. The observed increase in the \(H_{\mathrm {C}}\) value with decreasing pulse length (i.e., with increasing switching field frequency) is unambiguously related with the relaxation processes typical of single-domain ferromagnetic nanoparticles. However, the observed effect of the maximum applied field (\(H_{{\max }})\) on the \(H_{\mathrm {C}}\) value is assumed to be a feature of antiferromagnetic nanoparticles.

Magnetization hysteresis loops of tin samples with an inverted opal structure are presented. The sample formed by tin particles with the size of 70 and 128 nm is found to be a type-I superconductor. The tin sample formed by 80 and 42 nm particles demonstrates an analog of intertype superconductivity: features of both type-I and II superconductors are observed on the magnetization isothermal curves. A behavior of the irreversible and reversible magnetizations supports coexistence of type-I and II superconducting nanoparticles in this sample.

Near the Curie temperature T-C = 30.3 K, the temperature dependences of the magnetization and heat capacity of a single-crystal ferromagnet PbMnBO4 in the magnetic fields of 1, 3, 10 and 30 kOe are studied. In the strong magnetic fields, both the magnetic contribution to the specific heat and the nonlinearity of the field dependences of the magnetization are maintained up to the temperatures exceeding T-C more than twice. It is assumed that in PbMnBO(4 )the difference between T-C, the paramagnetic Curie temperature theta = 49 K and the broad temperature region above T-C where the magnetic contribution to the specific heat is significant is due to the quasi-one-dimensional character of the magnetic structure of this ferromagnet. Using both the estimation of TC from the Ginzburg-Landau field theory and the theta value, the total exchange interaction parameters 2J approximate to 40.4 K (intrachain) and z'J' approximate to 8.8 K (interchain) are determined, with z' = 4 being the number of neighboring chains. The estimation shows that the Ginzburg-Landau field theory describing the quasi-one-dimensional behavior of PbMnBO4 is well applicable in the temperature range from to T = S(2)J approximate to 80 K. Above this temperature, the mean field approximation with the exchange parameter lambda(theta) based on the paramagnetic Curie temperature theta describes well the experimental temperature dependences of the magnetization in the strong magnetic field and the specific heat is determined by the lattice contribution.