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Purpose The purpose of this paper is to verify results related to losses in the core of a brushless DC prototype motor, obtained using its computer FE models, by experimental tests on manufactured machines. The paper focuses on the comparison of losses in the core of a machine with a classical stator core made of an iron–silicon material (Fe–Si) and a new one made of a modern METGLAS material. Design/methodology/approach Computer models of the prototype motors were created using FEM. The designed machines were manufactured, and experimental tests were performed. To achieve high frequencies in rotating magnetic fields, motors with a stator to rotor pole ratio of 9/12 were built. Twin rotor approach was applied, as two identical rotors were built along the two geometrically identical stators made of different core materials. Findings Experimental studies have shown the superiority of the METGLAS material over the classical Fe–Si material. Material parameters were measured directly on the prepared cores as library data used in the simulation may be incorrect due to technological processes during core production, which was also verified. Problems related to twin rotor approach have been identified. Solution to the problem has been suggested. Necessity of 3D FEM modelling was identified. Originality/value The main source of originality is that METGLAS material used in the prototype machines was developed and manufactured by the authors themselves. Original approach to core parameter evaluation based on simplified methodology has been suggested. Another original part is a simplified methodology applied to loss measurement during no-load test.

High-entropy ferrites (HEFs) are a new group of high-entropy oxides with unique magnetodielectric properties that offer a wide array of possibilities for high-frequency applications. Various ions were introduced at octahedral sites in the spinel structure to test the role of the high-entropy structure’s formation on its properties. The structural analysis confirmed the formation of single-phase spinel structure even for (FeCoNiMg)(FeCr)2O4 HEF. Dielectric studies showed that introducing Mg2+ and Cr3+ ions increased electrical conductivity and dielectric losses over a wide frequency range. Low frequency (from 0.8 to 1.5 GHz) studies showed that for (FeCo)Fe2O4 and (FeCoNi)Fe2O4 ferrites reflection losses (RL) are negligible, while for both (FeCoNiMg)Fe2O4 and (FeCoNiMg)( FeCr)2O4 ferrites RL higher than 90% were observed. The temperature dependence on the absorption properties was confirmed for (FeCoNiMg)(FeCr)2O4 HEF. The highest absorption window was observed for 343 K, for which RL higher than 90% appears from 1.25 to 1.5 GHz. The possibility of the 3D printing of microwave absorption composites from HEFs was also tested. It was confirmed that the addition of (FeCoNiMg)(FeCr)2O4 HEF drastically increases the absorption properties up to 85.5% at 2.72 GHz for the absorber with the same thickness as made from the pure acrylonitrile butadiene styrene (ABS). Interestingly, the EMI shielding properties of these composites are mainly related to the dielectric losses improved by the addition of entropy stabilised ferrites in 3D printed composites with various ferrite concentrations.

The effect of Nb content on microstructure, mechanical properties and superelasticity was studied in Ti-Nb alloys fabricated by powder metallurgy route using mechanical alloying and spark plasma sintering. In the microstructure of the as-sintered materials, undissolved Nb particles as well as precipitations of α-phase at grain boundaries of β-grains were observed. In order to improve the homogeneity of the materials, additional heat treatment at 1250 °C for 24 h was performed. As a result, Nb particles were dissolved in the matrix and the amount of α-phase was reduced to 0.5 vol.%. Yield strength of the as-sintered alloys decreased with Nb content from 949 MPa for Ti-14Nb to 656 MPa for Ti-26Nb, as a result of the decreasing amount of α-phase precipitations. Heat treatment did not have a significant effect on mechanical properties of the alloys. A maximum recoverable strain of 3% was obtained for heat-treated Ti-14Nb, for whichAsandAftemperatures were − 12.4 and 2.2 °C, respectively.

Modelling the transient simulation of magnetic circuits is the crucial process for development of modern switching mode power converters. Such models are especially important for newly developed magnetic materials, such as amorphous alloys. Paper presents the gyrator-capacitor model of inductive element with core made of high permeability, Co-based amorphous alloy. Parameters of the model were identified during Nedler-Mead method based optimization process. Presented results of modelling confirm that model can be used for SPICE simulations; however, the accuracy of losses modeling is limited in the wide range of frequencies.

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe72−xNi8Nb4CuxSi2B14 alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔGamorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔGmix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures Tx1onset and Tx1 of the alpha-iron phase together with the activation energy Ea for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 104 Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).

The complex structural and magnetic studies of the annealed rapidly quenched Cu-free Fe72Ni8Nb4Si2B14 alloy (metallic ribbons form) are reported here. Based on the calorimetric results, the conventional heat treatment process (with heating rate 10 &deg, C/min and subsequent isothermal annealing for 20 min) for wound toroidal cores has been optimized to obtain the least lossy magnetic properties (for the minimum value of coercivity and magnetic core losses at 50 Hz). For optimal conditions, the complex permeability in the 104&ndash, 108 Hz frequency range together with core power losses obtained from magnetic induction dependence up to the frequency of 400 kHz was successfully measured. The average and local crystal structure was investigated by the use of the X-ray diffraction method and the transmission electron microscopy observations and proved its fully glassy state. Additionally, for the three temperature values, i.e., 310, 340 and 370 &deg, C, the glass relaxation process study in the function of annealing time was carried out to obtain a deeper insight into the soft magnetic properties: magnetic permeability and cut-off frequency. For this type of Cu-free soft magnetic materials, the control of glass relaxation process (time and temperature) is extremely important to obtain proper magnetic properties.

Influence of Cu content on thermodynamic parameters (configurational entropy, Gibbs free energy of mixing, Gibbs free energy of amorphous phase formation), crystallization kinetics, structure and magnetic properties of Fe86-xCuxB14 (x = 0, 0.4, 0.55, 0.7, 1) alloys is investigated. The chemical composition has been optimized using a thermodynamic approach to obtain a minimum of Gibbs free energy of amorphous phase formation (minimum at 0.55 at.% of Cu). By using differential scanning calorimetry method the crystallization kinetics of amorphous melt-spun ribbons was analyzed. It was found that the average activation energy of &alpha, Fe phase crystallization is in the range from 201.8 to 228.74 kJ/mol for studied samples. In order to obtain the lowest power core loss values, the isothermal annealing process was optimized in the temperature range from 260 &deg, C to 400 &deg, C. Materials annealed at optimal temperature had power core losses at 1 T/50 Hz&mdash, 0.13&ndash, 0.25 W/kg, magnetic saturation&mdash, 1.47&ndash, 1.6 T and coercivity&mdash, 9.71&ndash, 13.1 A/m. These samples were characterized by the amorphous structure with small amount of &alpha, Fe nanocrystallites. The studies of complex permeability allowed to determine a minimum of both permeability values at 0.55 at.% of Cu. At the end of this work a correlation between thermodynamic parameters and kinetics, structure and magnetic properties were described.

This paper presents results of a research work aimed at designing, building and carrying out performance tests with a cooling device model utilizing linear motion of the magnetic field source and cyclic flow of a coolant through regenerator. The device incorporates two identical regenerators from 34 gadolinium plates each and a magnetic field source of 1 T. The working liquid was mixture of water and glycol with the specific heat of about 4000 J/kgK. The magnetic field source was introduced with maximum flux density of 1 T. The maximum temperature span measured on the heat exchangers was 10.3 K. Original solutions of the mechanical drives have been applied so as to achieve suitable synchronization and operating frequency of the model.

The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe3O4 nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 ± 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 × 10−4 S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges.

In the present work, we investigated in detail the thermal/crystallization behavior and magnetic properties of materials with Fe84.5-xCoxNb5B8.5P2 (x = 0, 5, 10, 15 and 20 at.%) composition. The amorphous ribbons were manufactured on a semi-industrial scale by the melt-spinning technique. The subsequent nanocrystallization processes were carried out under different conditions (with/without magnetic field). The comprehensive studies have been carried out using differential scanning calorimetry, X-ray diffractometry, transmission electron microscopy, hysteresis loop analyses, vibrating sample magnetometry and Mössbauer spectroscopy. Moreover, the frequency (up to 300 kHz) dependence of power losses and permeability at a magnetic induction up to 0.9 T was investigated. On the basis of some of the results obtained, we calculated the values of the activation energies and the induced magnetic anisotropies. The X-ray diffraction results confirm the surface crystallization effect previously observed for phosphorous-containing alloys. The in situ microscopic observations of crystallization describe this process in detail in accordance with the calorimetry results. Furthermore, the effect of Co content on the phase composition and the influence of annealing in an external magnetic field on magnetic properties, including the orientation of the magnetic spins, have been studied using various magnetic techniques. Finally, nanocrystalline Fe64.5Co20Nb5B8.5P2 cores were prepared after transverse thermo-magnetic heat treatment and installed in industrially available portable heating equipment.

The structure of single-wall carbon nanohorns produced by direct vaporization of graphite has been studied using X-ray and neutron diffraction supported by molecular dynamics. The supplementary thermogravimetric and X-ray photoelectron spectroscopy studies have been performed to prove the structural and elemental purity of the sample. Afterwards, the pair correlation function has been calculated to represent the collected data in a real space representation. The computer-generated models consisted mainly of defected single-wall carbon nanotubes 45 A in diameter. The calculated structure factors and pair correlation functions well reproduce the experimental data. The structural disorder in the form of topological point defects such as the Stone-Thrower-Wales, single-vacancy and double-vacancy defects have been introduced to fit the experimental data.

The spark plasma sintering technique was successfully used to transform fullerene extract into glass-like carbon. The sintered sample was characterized via thermogravimetry, scanning electron microscopy, X-ray photoelectron spectroscopy, the X-ray and neutron diffraction. To reconstruct the atomic scale structure the diffraction results were combined with computer simulations. The comparative analysis was performed in the form of the structure factor and the pair correlation function in the reciprocal and direct space. In the first approach the two different concepts of graphite-based models have been verified. For such constructed models the pair correlation functions maxima positions indicate the strong differences in comparison with the experimental data. In the second approach the proposed models were constructed successively on the icosahedral from C960 up to C3840 fullerenes fragments. The final model consists of triple layer fullerene C3840-like fragments in which the isolated pentagon presence guaranties the stronger curvature. The calculated pair correlation function fits the experimental data well and therefore proves that the atomic structure of sintered glass-like materials originated from C60/C70 fullerene extract consists of defected fullerene C3840-like fragments. The curvature was assured by isolated pentagon, but the disorder of surrounded hexagonal lattice was modeled and properly reconstructed by the Stone-Thrower-Wales topological defects.

Reconstruction of large cavities in the skull and facial regions is important not only to restore health but also for the correction of facial distortions. Every visible deformity in the facial region of the patient affects their mental wellness and perception by society, entailing both, deterioration of health, but also a decrease in the performance in society, which translates into its productivity. With the progressive degradation of the natural environment, cancer, in the coming years, will be on the leading causes of morbidity and mortality. The review focuses on two main aspects: (i) the causes of injuries leading to the necessity of removal of orbital cavities occupied by the tumor and then their reconstruction, with the focus on the anatomical structure of the orbital cavity, (ii) the materials used to reconstruct the orbital cavities and analyze their advantages and disadvantages. The manuscript also underlines the not yet fully met challenges in the area of facial- and craniofacial reconstruction in people affected by cancer.

The effect of substitution of Fe by Cu on the crystal structure and magnetic properties of Fe72−xNi8Nb4CuxSi2B14 alloys (x = 0.6, 1.1, 1.6 at.%) in the form of ribbons was investigated. The chemical composition of the materials was established on the basis of the calculated minima of thermodynamic parameters: Gibbs free energy of amorphous phase formation ΔGamorph (minimum at 0.6 at.% of Cu) and Gibbs free energy of mixing ΔGmix (minimum at 1.6 at.% of Cu). The characteristic crystallization temperatures Tx1onset and Tx1 of the alpha-iron phase together with the activation energy Ea for the as-spun samples were determined by differential scanning calorimetry (DSC) with a heating rate of 10–100 °C/min. In order to determine the optimal soft magnetic properties, the wound cores were subjected to a controlled isothermal annealing process in the temperature range of 340–640 °C for 20 min. Coercivity Hc, saturation induction Bs and core power losses at B = 1 T and frequency f = 50 Hz P10/50 were determined for all samples. Moreover, for the samples with the lowest Hc and P10/50, the magnetic losses were determined in a wider frequency range 50 Hz–400 kHz. The real and imaginary parts of the magnetic permeability µ′, µ″ along with the cut-off frequency were determined for the samples annealed at 360, 460, and 560 °C. The best soft magnetic properties (i.e., the lowest value of Hc and P10/50) were observed for samples annealed at 460 °C, with Hc = 4.88–5.69 A/m, Bs = 1.18–1.24 T, P10/50 = 0.072–0.084 W/kg, µ′ = 8350–10,630 and cutoff frequency at 8–9.3 × 104 Hz. The structural study of as-spun and annealed ribbons was carried out using X-ray diffraction (XRD) and a transmission electron microscope (TEM).

In the present work, the chemical hydrogenation process of La(Fe,Si) 13 compounds has been shown. It was found, that the La(Fe,Si) compound can be easily saturated with hydrogen by performing reaction with 0.6 M hydrochloric acid (HCl) for 2 h. After reaction, the heat treatment process is necessary to make hydrogenated powder homogenous. For the LaFe 11.8 Si 1.2 micronized ( 11.8 Si 1.2 ).

The magnetocaloric effect in the MnxFe2−xP1−yGey intermetallic compounds with the amount of Mn in the range of x = 1.05 to 1.17 and amount of Ge in the range of y = 0.19 to 0.22 has been studied. It was found that a higher Ge/P ratio causes an increase in Curie temperature, magnetocaloric effect at low field (up to 1 T), activation energy of structural transition and a decrease in thermal hysteresis, as well as transition enthalpy. Contrary to this observation, higher Mn/Fe ratio causes a decrease in Curie temperature, slight decrease of magnetocaloric effect at low magnetic field, and an increase in thermal hysteresis. Simultaneous increase of both ratios may be very advantageous, as the thermal hysteresis can be lowered and magnetocaloric effect can be enhanced without changing the Curie temperature. Some hints about optimization of the composition for applications at low magnetic fields (0.5 T to 2 T) have been presented.

The magnetocaloric effect in the MnFeP0.35As0.65−xSix intermetallic compounds, prepared via solid-state sintering was studied. Adiabatic temperature and magnetic entropy changes were obtained in order to characterize these compounds. The substitution of silicon for arsenic leads to a significant enhancement of the magnetocaloric effect for silicon amount x = 0.11. The adiabatic temperature change increased from 2.3 to 3.3 K for the magnetic field change from 0 to 1.7 T. This improvement has been correlated with the increase of crystalline cell volume and change of lattice constants. Additionally, the structure of pure MnFeP0.33As0.67 has been modeled in order to check the spin alignment within the framework of ferromagnetic collinear model.

Several papers have appeared in recent years on the application of the amorphous soft magnetic materials in the stators of the electric motors. In our previous work, we demonstrated that the replacement of a slotless stator from the FeSi electrical steel with the stator from an amorphous alloy Metglas 2605 SA1 in a high-speed permanent magnet brushless direct current (PMBLDC) motor resulted in a substantial decrease of power losses in this stator, even by three times at the rotary frequency of 70 000 r/min. This paper was concentrated on the development of the cores for stators with half-open slots, which are technologically more difficult to produce than the slotless cores. The cores were made by cutting out suitable amount of $25~\mu \text{m}$ -thick rings from the FeSiB amorphous ribbon by a laser technique, followed by stacking up the rings and their consolidation, and suitable heat treatment of the compressed stacks. Next, the measurements of the magnetic properties of the sample cores with half-open slots were made using the Remacomp C-1200 hysteresisgraph and the Lakeshore 450 Gaussmeter. Based on the results of measurements, the sample cores of different heights (17.5 and 10 mm) were selected for application in a stator of the prototype high-speed PMBLDC motor, 800 W in rated power and with a maximum rotary speed of 60 000 r/min. The preliminary performance tests with this prototype motor showed that after 1 h of uninterrupted operation, the temperature of a motor housing did not exceed 60 °C. It was also found that the operating efficiency of the PMBLDC motor incorporating a stator with half-open slots, made from an amorphous material, was almost 90% over a wide range of torques (from 40 to 140 mN $\cdot \text{m}$ ).

This paper describes the magnetic cooling device model designed and built at the Institute of Non-Ferrous Metals in Gliwice, which utilizes reciprocating motion of a magnetic field source and a cyclic flow of a coolant through regenerator. The regenerator made from gadolinum made it possible to obtain an adiabatic temperature change of 2.5 K at the magnetic field of 0.8 T. The magnetic field source was built using neodymium magnets according to our own technology. For the heat transfer, a liquid having the specific heat of about 4000 J/(kg K) has been applied. We have also developed and applied a special driving system enabling reciprocating motion of the magnetic field source and of the pistons in the hot and cold heat exchangers. The tests were made with this cooling model showing that it was possible to obtain, at the frequency of 0.5 Hz, the liquid temperature gradient of 4 K. The potential energy savings resulting from application of this device have been evaluated and compared with the literature data presenting a pre-industrial prototype of the magnetic refrigerator utilizing similar solutions to those applied in our cooling model.

The magnetic properties correlated with crystal structure of soft magnetic ribbons of the nominal composition Fe81.3−xCoxMo0.2Cu0.5Si4B14 synthesized by a melt spinning technique are reported. The crystallization process was monitored by differential scanning calorimetry (DSC) that allows identification of the primary crystallization temperature. Thereafter crystallization process is being optimized by changing heat treatment parameters in order to get best possible magnetic properties. The resulting crystal structure of the properly annealed cores has been investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) methods. It was found that the structure consists of α-Fe(Co,Si) nanograins with the mean size of 20 nm. Additionally, the magnetic saturation and coercivity from the measured hysteresis loops of studied samples have been determined. The microstructure was further correlated with Co content and nanograins size in order to discuss its impact on magnetic properties.

In this work, a detailed microstructural investigation of as-melt-spun and heat-treated Fe67Co20B13 ribbons was performed. The as-melt-spun ribbon was predominantly amorphous at room temperature. Subsequent heating demonstrated an amorphous to crystalline &alpha, (Fe,Co) phase transition at 403 &deg, C. In situ transmission electron microscopy observations, carried out at the temperature range of 25&ndash, 500 &deg, C and with the heating rate of 200 &deg, C/min, showed that the first crystallized nuclei appeared at a temperature close to 370 &deg, C. With a further increase of temperature, the volume of &alpha, (Fe,Co) crystallites considerably increased. Moreover, the results showed that a heating rate of 200 &deg, C/min provides for a fine and homogenous microstructure with the &alpha, (Fe,Co) crystallites size three times smaller than when the ribbon is heated at 20 &deg, C/min. The next step of this research concerned the influence of both the annealing time and temperature on the microstructure and coercivity of the ribbons. It was shown that annealing at 485 &deg, C for a shorter time (2 s) led to materials with homogenous distribution of &alpha, (Fe,Co) crystallites with a mean size of 30 nm dispersed in the residual amorphous matrix. This was reflected in the coercivity (20.5 A/m), which significantly depended on the volume fraction of crystallites, their size, and distribution.

This paper focuses on the phenomenon of the magnetic flux density dispersion Bd on the gaps of the Fe73.5Cu1Nb3Si13.5B9 multi-gap nanocrystalline block core. Present state-of-the-art shows, that there is no comprehensive knowledge about the value of the magnetic flux density dispersion Bd on the gaps of nanocrystalline block core and the possibilities of its minimisation. The magnetic flux density dispersion Bd is the source of local eddy currents, which are the cause of increase of power loss and temperature in the chokes’ core. To discuss the effect of gap width and the method of its filling on the power losses in the core, the comparison between inserts of Teflon and magnetic mat composed of 70% Fe53.9Co29.1B13Nb1Si2Cu1 powder with a fraction of 20–36 µm and 30% Ultimeg epoxy resin 2004L was performed.

In this paper the influence of copper addition on the formation of the amorphous phase and the nanocrystallization process of Fe79.8−xCo2CuxMo0.2Si4B14 (x = 0, 0.25, 0.5, 0.75, 1, 1.5, 2) ribbons was described. The formation of crystalline phases was described using differential scanning calorimetry, X-ray diffractometry, Mossbauer spectroscopy and transmission electron microscopy. It was confirmed that the addition of copper decreases the glass forming ability, while facilitating the process of nanocrystallization. The analysis of the Avrami exponent allowed to state, that for fully amorphous alloys the crystallization of the α-Fe phase is associated with diffusion-controlled growth with decreasing nucleation rate and the Fe2B phase with interface controlled growth with increasing nucleation rate. Additionally, with increasing copper addition onset temperature of crystallization of α-Fe phase shifts to lower values, whereas for second, Fe2B phase, these changes are not so visible. Optimization of the annealing process of toroidal cores made from amorphous ribbons with different copper content allowed to obtain nanocrystalline, soft magnetic materials characterized by low coercivity ~9 A/m and high saturation induction of about 1.6 T. Analysis of transmission electron microscope images and electron diffraction confirmed that high magnetic parameters are related to the coexistence of the amorphous and nanocrystalline phases, which was confirmed also by Mossbauer spectroscopy.

GdFeSi silicide is a strong ferromagnet with Curie temperature (Tc) equal to 118 K. The substitution of cobalt for iron continuously suppresses ferromagnetism of the former compound, while it changes magnetic transition temperature nonlinearly. When the molar amount of cobalt reaches 0.4, the temperature of magnetic transition reaches minimal value i.e, 70 K. For larger amount of cobalt, magnetic transformation temperature rises well above 200 K and the antiferromagnetic interactions become dominant. In the present work we have found that the magnetic transformation temperature can be strictly correlated with the lattice constant c, which determines the distance between gadolinium layers as well as distance between neighboring gadolinium atoms in one layer. These results correspond to the change of amplitude of magnetocaloric effect which is being suppressed when the amount of cobalt increases. Adiabatic temperature change is equal to 2 K during the magnetic field cycle 0–1.7 T for pure GdFeSi, while no temperature change is observed during the same cycle for pure GdCoSi because of its antiferromagnetic character.

In this paper, crystallization behavior of BCC iron phase in two Finemet-type ribbons with different cobalt content has been studied. Studied ribbons consist of 58.8 and 65 M percents of cobalt (Fe 14.7 Co 58.8 Cu 1 Nb 3 Si 13.5 B 9 and Fe 13.8 Co 65 Cu 0.6 Nb 2.6 Si 9 B 9 ). Identification of crystallized phase has been performed by means of X-ray diffraction and Neutron Diffraction. Kinetics parameters of this process have been obtained through the Differential Scanning Calorimetry measurements with different heating rates. The main aim of this work was to check the correlation between the kinetic parameters such as activation energy, rate constant and crystallization difficulty and the cobalt content in the studied ribbons. It was shown that the slight increase of cobalt amount leads to the significant change of activation energy from 300 to 250 kJ/mol.

Intermetallic compounds with the overall formula Mn1.1Fe0.9P0.5As0.5−xGex (x varies from 0 to 0.1) were investigated in order to study their magnetocaloric effect by monitoring the adiabatic temperature change, magnetic entropy change and their relation to structural parameters. It was found that the maximum of magnetocaloric effect was achieved for x = 0.02. Adiabatic temperature change for consolidated powder was equal to 2.75 K for the magnetic field change ΔB = 1.7 T for the sample with x = 0.02. For the pure non-doped sample, this parameter is much lower: ΔTad = 1.7 K @ ΔB = 1.7 T. This result was correlated with the change of structural parameters such as lattice constants and the unit cell volume.

The influence of Al substitution for Sn on magnetocaloric properties and exchange bias behavior in Ni48Mn39.5Sn12.5−xAlx (x=0, 1, 2, 3) melt spun ribbons have been investigated. All the studied ribbons undergo a martensitic and reverse transformation. At low temperature martensite region, below 100 K, the alloys exhibit exchange bias effect, which appears to enhance with the increase of Al concentration. The loop shift difference (ΔHE) of up to 7960 A m−1 is recorded between the ribbon containing no Al and the ribbon with x=3. The presence of exchange bias behavior in these samples is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions. The magnetic entropy change and refrigerant capacity are evaluated for the ribbons studied around both the structural and magnetic transformations under the applied magnetic field induction of 2 T. The maximum entropy change around the magnetic transition and around the structural transition is reported for the Ni48Mn39.5Sn12.5 ribbon, and the entropy values amount to 1.8 and 7.8 J kg−1 K−1, respectively.

The rapidly quenched soft magnetic materials have found many practical applications in power electronics, electric engineering, telecommunications, and other industrial sectors. The aim of this paper was to present the results of a research on fabrication technology of the amorphous and nanocrystalline cores intended for: 1) soft magnetic cores for the stators of the high-speed permanent magnet brushless direct current (PMBLDC) motors; 2) nanocrystalline soft magnetic cores for application in high-frequency power conversion; and 3) three-limb amorphous cores for the three-phase distribution transformers. The cores intended for the stator of the high-speed PMBLDC motor were made from the Metglas 2605 SA1 ribbon and then subjected to the performance tests in a model of an electric motor. The research on soft magnetic materials for high-frequency high-power conversion was concentrated on the Finemet rectangular cores with a gap and the composite ones with distributed gap, and the comodified Finemet cores with the induced transverse magnetic anisotropy. The three-limb cores for 400 kVA three-phase distribution transformer were made from the Metglas 2605 SA1 ribbon and subjected to the performance tests in electricity distribution network. It was found that all the amorphous and nanocrystalline cores fabricated under this paper enable considerable reduction in power losses.

An effect of interlaminar insulation on the dynamic magnetic properties of the tape-wound FeNiCuNbSiB-type nanocrystalline cores was investigated. This insulation was prepared by three methods. After thermomagnetic treatment of toroidal cores selected types of suitably chosen varnishes were applied onto the core edges so as to enable their in-depth penetration thus forming the desired insulation. In the final stage of thermomagnetic treatment, conducted initially under protective atmosphere of argon, oxygen was introduced to the process to enable formation of interlaminar oxide layer. Finally, the ribbon was coated with SiO layer prior to its winding into the core. Then, dynamic magnetic properties of the cores were measured within a frequency range from 50 Hz to 100 kHz. It was found that the use of a modified acrylic-type resin resulted in the decrease of the Fe73.8Ni5Cu0.6Nb2.6Si9B9 core losses at higher frequencies. In the cores with an oxide insulation, reduction of power losses was observed at lower frequencies. The use of interlaminar SiO insulation resulted in considerable reduction of core losses above the frequency of 5 kHz. The results of this paper can be practically applied in the production of nanocrystalline cores for power electronic equipment.

The atomic structure of commercially available nanographene platelets has been studied by high energy X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and molecular dynamics simulations using the reactive empirical bond order potential. Atomic models of the structure have been constructed and then relaxed using the molecular dynamics method and the model based simulations are compared with the experimental data both in reciprocal and real space. All model relaxations and the X-ray diffraction experiments have been carried out at 300 K. The proposed models consisting of about 2500 carbon atoms arranged within four graphitic layers with a diameter of 46 A, reproduced correctly all features of the experimental data. The atomic arrangement within an individual layer can be described in terms of the paracrystalline ordering, in which lattice distortions propagate proportionally to the square root of interatomic distances. The paracrystalline structure was simulated by introducing the topological point defects such as the Stone–Thrower–Wales defects, single- and double-vacancies, randomly distributed in the network. Such defects lead to curvature of individual layers and this effect was also analyzed. The generated models are related to the observations by high-resolution transmission electron microscopy.

This paper presents results of a research work related to the development of the production technology of the amorphous cores designed for application in permanent magnet brushless direct current (PMBLDC) motors. The cores were made from the Metglas 2605 SA1 amorphous ribbon, from which rings of the specific external and internal diameters were cut using a laser technique. Next, the rings were stacked up so as to form a core of a required height, subjected later to the consolidation by pressing, followed by an appropriate heat treatment. Finally, the cores were coated with an epoxy resin to protect them against delamination and used as stators in a prototype high-speed electric motor, 1 kW in rated power and 70 000 rpm in a rotary speed. The motor incorporating these amorphous cores was subjected to the performance tests, which confirmed their proper operation and satisfactory mechanical characteristics and efficiency. It was found that power losses in the stators from the amorphous material were considerably smaller than those in the conventional stators from the silicon steel, and they did not exceed 7 W. Therefore, an application of the amorphous soft magnetic materials in the high-speed PMBLDC motors may contribute to eliminating the need of using additional cooling systems in these motors.

Ni2MnGa alloy exhibits significant magnetocaloric effect due to structural and magnetic transition, which take place at similar temperature range. In this report we present band structure calculations for Ni2MnGa doped with Cu performed within KKR-CPA scheme. We also calculated the estimated temperature of the magnetic transition as a function of dopant concentration within Mean-Field-Approach (MFA). Our calculations show that the Curie temperature increases with Cu doping in agreement with recent experimental data.