Thermomagnetic Treatment Research Articles

Preparation of strontium hexaferrite based materials by solution combustion: the effect of charges arising in precursors and an external magnetic field

The formation of electric charges during the synthesis of complex oxide materials based on strontium hexaferrite SrFe12O19, including doped with lanthanum and cobalt ions, via the combustion of nitrate-organic precursors has been established. Precursors included polyvinyl alcohol or glycine as organic component. The intensity of charge generation was lower for precursors containing a larger amount of organic component. Data on the magnetic characteristics of the samples were obtained: magnetization, coercive force. The influence of an external magnetic field during the synthesis of hexaferrites significantly affected the coercive force of the samples and allowed to increase its values due to the formation of extended ensembles of nanoparticles. At the same time, such an effect on samples with a relatively low level of charge generation during precursor combustion was more effective. The relationship between the factors influencing the formation of extended aggregates is analyzed. The Sr0.8La0.2Fe11.8Co0.2O19 samples had the maximum coercive force. One of the techniques for increasing the coercive force is a two-stage thermomagnetic treatment, including a low-temperature stage. The formation of branched extended structures at the macro- and micro-levels was found during the combustion of glycine-containing precursors.

Design and development of thermo-electromagnetic system for spinodal decompositions of FeCrCo alloys

Permanent magnets are essential components of electromechanical devices. Majority of magnets are used in permanent magnet motors that have extensive application in relation to energy efficiency and sustainability like electric vehicles. This research is aimed for efficient manufacturing of FeCrCo permanent magnets. Electromagnets could be utilized for the generation of continuous magnetic field to use in number of manufacturing processes. A two-pole electromagnet, comprising of two solenoids each having 2200 turns of copper wire, was developed. The system was designed to produce magnetic field up to 10 kilo Gauss for spinodal decomposition of FeCrCo alloy samples under thermomagnetic treatment process. Being rare earth free alloys, FeCrCo magnet is gaining research focus as an alternative magnetic alloy for advanced applications. The electromagnetic system design was refined and confirmed by using the Finite Element Method. The experimental values, of magnetic field generated by the two-pole electromagnet setup, were well close to the simulation results. The magnetizing setup was utilized to treat the FeCrCo magnetic alloy samples simultaneously at high temperature (700 °C) and magnetic field (7 kilo Gauss). This thermo-magnetic setup helped to improve the metallurgical structures of FeCrCo to grow and develop more efficiently. Treated samples of FeCrCo alloy demonstrated enhanced magnetic properties due to effective spinodal decomposition. The improvement in magnetic properties was attributed to the elimination of retained alpha phase and formation of more alpha-1 phase.

Influence of a Constant Magnetic Field on the Parameters of the Magnetoplastic Effect in Aluminum Alloy B95pch

The present work is devoted to the comprehensive experimental study of the magnetoplastic effect found in the aluminum alloy B95pch aged in a weak constant magnetic field. The data on chemical composition of aluminum alloy B95pch, modes of thermal and thermomagnetic treatments and main experimentally observed regularities of changes in values of microhardness, modulus of elasticity of separate local areas and phase composition of aluminum alloy B95pch, aged at temperature 140°С, time from 2 to 8 h, in a constant magnetic field with intensity 557.0 kA/m and in its absence are presented. It was found that the constant magnetic field significantly affects the strength properties and structure of aluminum alloy B95pch. The negative magnetoplastic effect has been detected, the value of which is 21%. It is observed that the constant magnetic field does not significantly affect the average grain size, however, the size and number of observed foreign inclusions within the grain become significantly smaller compared to aging in the absence of magnetic field. In addition, the imposition of the constant magnetic field on the phase formation process leads to the formation of a more distorted structure: the half-width of diffraction lines becomes wider. The results of microhardness and modulus of elasticity measurements of aluminum alloy B95pc were found to be correlated.

A Spin Valve-Based Rhombus-Shaped Micro-Object Implementing a Full Wheatstone Bridge.

Spin valves with a synthetic antiferromagnet were fabricated via magnetron sputtering. It was shown that the fabricated spin valve layers had a perfect microstructure and smooth interfaces, and therefore, an RKKY interaction dominated in the coupling of the ferromagnetic layers separated by a copper spacer. Rhombus-shaped micro-objects were fabricated from a single spin valve film. The thermomagnetic treatment procedure was found to form unidirectional anisotropy in the micro-object such that the values of the exchange bias fields in the rhombus' nonparallel sides were opposite in sign. For the CoFeNi/Ru/CoFeNi synthetic antiferromagnet, we determined the differences between the ferromagnetic layer thicknesses at which the thermomagnetic treatment formed the same exchange bias all over each rhombus' side. We also fabricated a sensor element in which each side of the rhombus was the shoulder of a Wheatstone bridge. After the thermomagnetic treatment procedure, each shoulder worked as an active magnetosensitive element, enabling the device to operate as a full Wheatstone bridge. The sensor output exhibited a step shape, high sensitivity to field changes, and significant magnetic hysteresis. Such characteristics are suitable for switching devices.

Influence of the pulsed magnetic field of the amplitude strength on the parameters of the magnetoplastic effect in aged Al–Si–Cu–Fe aluminum alloy

The results of a comprehensive experimental study of the influence of the pulsed magnetic field of the amplitude strength on the properties and characteristics of an Al–Si–Cu–Fe aluminum alloy during aging are presented. Data are presented on the modes of thermomagnetic treatment and the results of measurements of the microhardness, lattice parameter, and fine structure parameters of the alloy aged at a temperature of 175°С for 4 h in a pulsed magnetic field with a strength amplitude of 79.6–557.2 kA/m and in its absence. The main regularities of changes in the structure and properties of the metal alloy during annealing are formulated.

Effect of Field Annealing on Magnetic Properties of Magnetic Soft Iron–Germanium Alloys

Abstract—The concentration dependence of the magnetic properties of iron–germanium alloys before and after thermomagnetic treatment, which represents an annealing of alloy samples in the ferromagnetic state in a permanent or alternating magnetic field (magnetic field annealing – MFA), has been investigated. It is shown that before MFA, with an increase in the germanium content in the range of 3–30 at % Ge, the coercive force increases and the residual induction decreases. As a result of thermomagnetic treatment, in the alloy samples magnetic anisotropy is induced: the magnetic hysteresis loops become narrower, the residual induction increases, and the coercive force decreases. Thermomagnetic treatment is effective for Fe–Ge alloys with a germanium content from 6 to 18 at %, and its highest efficiency is observed at 12 at % Ge. Features of the structural state of iron–germanium alloys and their role in the formation of magnetic properties during annealing in a magnetic field are discussed.

Effects of thermomagnetic treatments on the magnetism of Cu–Al–Mn alloys

Effects of thermomagnetic treatments on the magnetism of Cu–Al–Mn alloys

Study of Synthetic Antiferromagnetic Nanostructures Based on CoFeB/Ru/CoFe

A study of the magnetic properties of synthetic antiferromagnetic nanostructures (SAF) has been carried out. In the SAF structure, two ferromagnetic layers separated by a nonmagnetic metal are coupled by the exchange RKKY interaction (Ruderman— Kittel—Kasuya—Yoshida), which has an oscillating character. The total magnetic moment of the SAF structure is minimal with an antiparallel configuration of the magnetization of the ferromagnetic layers, due to which the effect on the magnetic layers in the structure is reduced. The structures under study have a number of unique properties and are used in the elements of nonvolatile magnetoresistive memory, in magnetic field transducers, and in spin logic devices. The characteristics of the SAF of CoFeB/Ru/CoFe nanostructures with the Ru layer thickness corresponding to the second antiferromagnetic maximum are obtained. The magnetization reversal curves of SAF structures with Ru thickness of 2.1 nm, 2.3 nm and 2.5 nm have been studied. The optimal ratio of ferromagnetic layers was selected to reduce the magnetic moment of the SAF structure. A study of the effect of thermomagnetic treatment on the properties of the SAF nanostructure was carried out, which showed that there are no significant changes in the magnetization reversal, and the magnetic saturation field slightly increases. The curves of magnetization reversal of CoFeB/Ru/CoFe structures fixed by the antiferromagnetic layer are presented. In addition, magnetization reversal curves of spin-tunnel magnetoresistive nanostructures with an antiferromagnetic layer and a SAF structure are presented, and an analysis of the thermal stability of the structures with SAF is also carried out.

Формирование обменного смещения и анизотропия формы в микрообъектах на основе спиновых клапанов

Rhombus-shaped microobjects formed by strips of two micrometers wide were fabricated from the spin valve film. The influence of the shape anisotropy on the layers magnetic moment rotation during the spin valve magnetic reversal is studied. A method for two-stage thermomagnetic treatment in a direction-fixed magnetic field has been found. The method allows to obtain the opposite sign values of the exchange bias fields in the non-parallel rhombus sides. The direction of the formed exchange bias is determined by the deviation of the strip from the uniaxial anisotropy axis and from the magnetic field applied during thermomagnetic treatment. Based on a rhombus-shaped microobject made from a single spin valve film, the device is a Full Wheatstone bridge. Each side of the rhombus is an active magnetically sensitive element.

Методы увеличения магнитоэлектрического эффекта в композитных структурах: обзор

The article provides a review of various methods that can be used to increase the magnetoelectric (ME) effect in composite structures based on magnetostrictive and piezoelectric materials. It is shown that the use of adhesive technology and gradient structure, as well as thermal and thermomagnetic treatment of a magnetostrictive amorphous alloy of an ME structure make it possible to achieve a significant increase in the ME effect. To date, great efforts have been made to optimize the strain amplitude in the piezoelectric and magnetostrictive phases of multilayer ME materials. The use of various technologies in the manufacture of ME composites makes it possible, for example, to increase the sensitivity of magnetic field sensors for biomedical applications. Also, an increase in the ME effect opens up great prospects for further research.

Effect of thermally induced structural and compositional transformations on magnetic properties in FeMn/(Fe, Co, Ni, Fe20Ni80, Fe11Ni89, Co30Ni70) films

In this work a comparative systematic study of the crystal structure and magnetic properties of Fe50Mn50/(Fe, Co, Ni, Fe20Ni80, Fe11Ni89, Co30Ni70) films in as-deposited state and after subsequent vacuum thermomagnetic treatment at temperatures up to 400 °C was performed. Thermally induced changes in magnetic properties are described quantitatively and critical role of the interlayer diffusion leading to partial or complete (for Co layer) destruction of the antiferromagnetic layer is demonstrated. The result of such compositional changes is a significant decrease or disappearance of exchange bias.

Processing of silicon added Fe-Cr-Co hard magnetic alloy by two stage thermomagnetic treatment technique

Fe-Cr-Co is a typical spinodal decomposition type magnetic alloy. FeCrCo alloys being highly workable are important for slender feature designs and ductile applications. However, due to the rising prices of cobalt, research is increasingly being focused toward reducing the amount of cobalt in FeCrCo semi-hard magnetic alloys, without compromising on their magnetic properties. Silicon is ferrite stabilizer and therefore, can be utilized as a potential alloying element. Few researchers have reported work on addition of silicon in FeCrCo alloys, especially on the double isothermal magnetic field annealing. In this work, FeCrCo alloy with 2% silicon addition was produced and subjected to different heat treatments. An electromagnetic setup equipped with a tube furnace was designed based on Finite Element Method (FEM) analysis, and developed for thermomagnetic treatments. An increase in remanence for double thermomagnetic treatment was noted. This improvement could be attributed to the transformation of retained α phase into α1 phase. It was also observed that the squareness of the M-H curve improved with the double treatment.

Magnetically active coatings for electrical materials

The prospects of using nitride-oxide and magnesium phosphate electrical insulating coatings on thin strips of magnetically soft alloys based on silicon iron are considered. X-ray diffraction topography, powder figures, and magnetic measurements have shown that coatings create uniformly distributed tensile stresses in materials, increase uniaxial magnetic anisotropy, and reduce the volume of transversely magnetized domains and the width of longitudinally magnetized ones. This increases magnetic permeability and significantly decreases the coercive force, as well as eddy-current and total (by 20–25 %) magnetic losses. Tensile (magnetically active) coatings enhance the effect of subsequent thermomagnetic treatment of alloys.

Determination of Steel Losses and Optimization of the Thickness of the Transformer Magnetic Conductor Sheets

Currently, transformer manufacturers are tasked with creating energy-efficient devices with a reduction of steel losses of up to 44 %. Appropriate theoretical developments are needed for its implementation. With a reduction of eddy-current losses, caused, for example, by reduction of decrease in the thickness of the magnetic conductor sheets, hysteresis losses simultaneously increase. A similar effect is caused by changing the size of the crystal grain of steel, thermomagnetic treatment and other technological impacts. In this regard, the exact determination of the components of total losses in steel is an urgent problem, the solution of which would minimize total losses. The article analyzes the expressions that determine the specific losses for eddy currents and hysteresis through the parameters of the magnetic circuit, and states that this technique is too complicated for engineering calculations. Since eddy current losses are proportional to the square of the frequency, and hysteresis losses are proportional to the frequency in the first degree, simple calculated expressions of eddy current and hysteresis losses have been obtained using the wattmetric method. Based on the fact that the dependence of the magnetization loss on the thickness of the magnetic conductor plates is a decreasing linear function, and the eddy current loss is an ascending parabolic function, an expression of the optimal thickness of the plates has been found, the implementation of which makes the losses of steel minimal. This information will make it possible to minimize total steel losses more effectively by varying the design parameters and the material of the magnetic conductor. It is shown that the charted idling losses of transformers manufactured by different manufacturers differ by more than 30 % and can be rounded and underestimated; therefore it is advisable to obtain this parameter as a result of an experiment (idling experiment).

Optimization of Single α-Phase for Promoting Ferromagnetic Properties of 44Fe-28Cr-22Co-3Mo-1Ti-2V Permanent Magnet with Varying Co Concentration for Energy Storage.

The thermal stability and structural, microstructural and magnetic properties of (40 + x) Fe–28Cr–(26 − x) Co–3Mo–1Ti–2V magnets with x = 0, 2, 4 addition in cobalt content were investigated and presented. The magnetic alloys were synthesized by vacuum arc melting and casting technique in a controlled argon atmosphere. Magnetic properties in the alloys were convinced by single-step isothermal field treatment and subsequent aging. The alloys were investigated for thermal stability, structural, microstructural and magnetic properties via differential thermal analysis (DTA), X-ray diffractometery (XRD), optical microscopy (OM), field emission scanning electron microscope (FESEM) and DC magnetometer. Metallurgical grains of size 300 ± 10 μm were produced in the specimens by casting and refined by subsequent thermal treatments. The magnetic properties of the alloys were achieved by refining the microstructure, the optimization of conventional thermomagnetic treatment to modified single-step isothermal field treatment and subsequent aging. The best magnetic properties achieved for the alloy 44Fe–28Cr–22Co–3Mo–0.9Ti–2V was coercivity Hc = 890 Oe (71 kA/m), Br = 8.43 kG (843 mT) and maximum energy product (BH)max = 3 MGOe (24 kJ/m3). The enhancement of remanence and coercivity enabled by the isothermal field treatment was due to the elongation of the ferromagnetic phase and step aging treatment due to the increase in the volume fraction. This work is interesting for spin-based electronics to be used for energy storage devices.

Effect of thermomagnetic treatments on the domain structure of Finemet amorphous films

Thermomagnetic processing of films of the Finemet type with an easy magnetization axis in the plane under the action of a constant and rotating magnetic field was carried out in order to obtain an isotropic state. After heat treatment in a constant field, the easy magnetization axis was reoriented along the line of action of the field, as a result of which the domain walls were oriented along the new axis. After thermomagnetic treatment in a rotating field, regions with different anisotropy patterns, including isotropic regions, were revealed. Keywords: domain structure, thermomagnetic treatment, rotating magnetic field.

Влияние термомагнитных обработок на доменную структуру аморфных пленок типа файнмет

Thermomagnetic processing of films of the finemet type with an easy magnetization axis in the plane under the action of a constant and rotating magnetic field was carried out in order to obtain an isotropic state. After heat treatment in a constant field, the easy magnetization axis was reoriented along the line of action of the field, as a result of which the domain walls were oriented along the new axis. After thermomagnetic treatment in a rotating field regions with different anisotropy patterns, including isotropic regions, were revealed.

Effect of Co Substitution and Thermo-Magnetic Treatment on the Structure and Induced Magnetic Anisotropy of Fe84.5-xCoxNb5B8.5P2 Nanocrystalline Alloys.

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.

Comparison of magnetic and mechanical properties of powder Fe-Cr-Co alloys with different cobalt content obtained at various sintering temperatures

In present work, we studied the effect of sintering temperature and thermomagnetic treatment (TMT) on the magnetic hysteresis characteristics of the Fe-30Cr-8Co, Fe-30Cr-12Co and Fe-30Cr-16Co (wt. %) powder alloys. All investigated powder alloys, sintered at temperature range of 1100-1400 °C have a high level of magnetic properties ensuring their technical application. The highest values of magnetic properties for all three investigated powder alloys are observed after sintering at 1350 °C: Br = 1,28 T, Hc = 44,3 kA/m, BH(max) = 39 kJ/m3-for Fe-30Cr-8Co alloy; Br = 1,28 T, Hc = 48,2 kA/m, BH(max) = 39,2 kJ/m3-for Fe-30Cr-12Co alloy and Br = 1,23 T, Hc = 54,9 kA/m, BH(max) = 37,6 kJ/m3-for Fe-30Cr-16Co alloy. For Fe-30Cr-8Co alloy it was observed that additional annealing at 500 and 480 °C slightly increases the magnetic properties. For Fe-30Cr-12Co and Fe-30Cr-16Co alloys, there is no clear tendency regarding the effect of additional annealing on the magnetic properties. Compression tests of powder alloys Fe-30Cr-8Co and Fe-30Cr-16Co sintered in the temperature range 1100-1400 °C have shown that the yield strength σ0.2 of the Fe-30Cr-16Co alloy samples (970 – 1080 MPa) are higher compared to the Fe-30Cr-8Co alloy (710 – 930 MPa) throughout the entire sintering temperature range but Fe-30Cr-8Co alloy have a better ductility compared with Fe-30Cr-16Co alloy. Maximum values of σ0.2 were obtained on samples sintered at 1100 °C.

The Influence of Thermomagnetic Treatment of Cores of Amorphous Magnetic Materials on the Metrological Characteristics of Electromagnetic Transformers of Current

We consider a method of thermomagnetic treatment of amorphous magnetic material cores in a transverse constant magnetic field designed to improve the metrological characteristics of current transformers. The effectiveness of the method is due to a significant increase in the magnetic permeability of the cores of current transformers. The use of thermomagnetic processing makes it possible to increase their precision class.