Soft Magnetic Behavior Research Articles

Fabrication and Magneto-Structural Properties of Co2-Based Heusler Alloy Glass-Coated Microwires with High Curie Temperature

In this work, we were able to produce Co2FeSi Heusler alloy glass-covered microwires with a metallic nucleus diameter of about 4.4 µm and total sample diameter of about 17.6 μm by the Taylor–Ulitovsky Technique. This low cost and single step fabrication process allowed the preparation of up to kilometers long glass-coated microwires starting from a few grams of high purity inexpensive elements (Co, Fe and Si), for a wide range of applications. From the X-ray diffraction, XRD, analysis of the metallic nucleus, it was shown that the structure consists of a mixture of crystalline and amorphous phases. The single and wide crystalline peak was attributed to a L21 crystalline structure (5.640 Å), with a possible B2 disorder. In addition, nanocrystalline structure with an average grain size, Dg = 17.8 nm, and crystalline phase content of about 52% was obtained. The magnetic measurements indicated a well-defined magnetic anisotropy for all ranges of temperature. Moreover, soft magnetic behavior was observed for the temperature measuring range of 5–1000 K. Strong dependence of the magnetic properties on the applied magnetic field and temperature was observed. Zero field cooling and field cooling magnetization curves showed large irreversibility magnetic behavior with a blocking temperature (TB = 205 K). The in-plane magnetization remanence and coercivity showed quite different behavior with temperature, due to the existence of different magnetic phases induced from the internal stress created by the glass-coated layer. Moreover, a high Curie temperature was reported (Tc ≈ 1059 K), which predisposes this material to being a suitable candidate for high temperature spintronic applications.

Tuning the structural, optical and magnetic properties of NiCuZn (Ni0.4Cu0.3Zn0.3Fe2O4) spinel ferrites by Nb2O5 additive

Ni0.4Cu0.3Zn0.3Fe2O4 ferrites with various compositions (0–5 wt. %) of Nb2O5 additive were synthesized by the sol-gel method with an aim to investigate their physical properties. The analysis of Rietveld refined X-ray diffractograms confirms formation of ferrites with a single-phase spinel structure having space group Fd3m. The result indicates that there is an enhancement in the lattice parameter values with increasing Nb2O5 content. The nanoparticles in the shapes of spheres and cubes with few agglomerations were evident from field emission scanning electron microscope images of ferrites. The elemental analysis from energy dispersive X-ray spectrum confirms the stoichiometric occurrence of constituent elements within the prepared samples. The Raman spectra confirm the cubic spinel structure of the prepared ferrite samples. The Fourier transform infra-red spectra confirm the superseding of Nb5+ ions in the unit cell of NiCuZn ferrite. Oxidation states of the elements within the ferrite were confirmed by means of X-ray photoelectron spectroscopy. The UV–Visible diffused reflectance spectroscopy results show that the band gap energy values were reduced with the increasing wt.% of Nb2O5 additive in the ferrite. The Nb2O5 additive reduces the saturation magnetization and coercivity of all the ferrite samples. The study reveals that the controlled amount of Nb2O5 additive in NiCuZn ferrite can tune the soft magnetic behavior and optical parameters of the ferrite at room temperature.

Effect of Co addition on magneto structural characteristics of Ni50−xCoxMn30Al20 Heusler alloys obtained by mechanical alloying process

Off-stoichiometric Ni50−xCoxMn30Al20 Heusler alloys were prepared by mechanical synthesis to study their structure, microstructure, morphology, chemical composition, and magnetic properties as a function of Co addition and at high temperature, using X-ray diffraction, SEM-EDS analysis, and VSM technique. At the end of the milling process, homogeneous mixtures consisting mainly of agglomerated grains of rounded shape with some debris of MICA-shaped particles were formed. All alloys have a nanocrystalline structure with an ordered Heusler B2 phase at 800 K. With increasing magnetization temperature, the crystallite size increases significantly by >100%, however, the rate of microstrain decreases drastically due to the relaxation of residual stresses. High-temperature magnetic characterizations have shown that the addition of cobalt has a direct effect on the curie temperature of the alloys as well as on their magnetic parameters Hc, Mr, and Ms. As the percentage of Co decreases, the curie temperature drops until it reaches 300 K by replacing 5% of Ni with Co. Ni45Co5Mn30Al20 has the lowest curie temperature close to 300 K and exhibits a soft magnetic behavior characterized by high saturation magnetization (Ms), and low coercivity (Hc) with an interesting coupling-magnetic exchange, which makes it a suitable candidate for soft magnetic applications.

Room temperature ferromagnetism in oxygen-deficient gallium oxide films with cubic spinel structure

Oxygen-defective gallium oxide (Ga2O3-x with 0.4 < x < 0.7) thin films with cubic spinel structure were deposited on c-cut epi-polished sapphire wafers using thermal evaporation technique by keeping specific values of oxygen partial pressure in the evaporation chamber. The preparation method and post-treatment conditions induced distinct oxygen stoichiometries in the films which exhibit a ferromagnetic-like behavior at room temperature. Despite the measured saturation magnetization values do not exhibit a straightforward correlation to the oxygen stoichiometry of the films, the presence of oxygen vacancies and defects is presumably the origin of the unconventional magnetic behavior. Strong magnetic irreversibility exhibit by the magnetization measurements performed using field-cooling and zero-field-cooling protocols indicate the presence of disordered magnetic moment distributions which are likely non-collinear. Theoretical and experimental results available in the literature corroborate with the assumptions that oxygen vacancies and defects appear as the main reason for room-temperature ferromagnetism. All films exhibit soft magnetic behavior at room temperature, exhibiting remanent magnetizations between 7% and 20% of the saturation magnetization which saturated magnetic moments is estimated as 0.43 and 1.24 Bohr magneton per oxygen vacancy. The present results extend the functionalities of this interesting material, which is already investigated for applications in several technological areas, for possible uses in the areas of spintronics and emerging areas of the optospintronics.

Sol-gel extended hydrothermal pathway for novel Cd-Zn co-doped Mg-ferrite nano-structures and a systematic study of structural, optical and magnetic properties

The novel study of Cd-Zn co-doped Magnesium ferrites CdxZn1-xMg0.25Fe1.75O4 (where x = 0, 0.25, 0.75, 0.50, and 1.00) has been made successfully by adopting a facile sol-gel extended hydrothermal pathway. Structural, optical, and magnetic behavior of the Cd-Zn co-doped Magnesium ferrites were systematically analyzed. From the X-ray Diffraction (XRD) patterns it was confirmed that the prepared samples have a cubic spinel structure. Scanning electron microscopic (SEM) study revealed the agglomerated and irregular shape of Cd-Zn co-doped Magnesium ferrites nanoparticles. Fourier transforms infrared (FTIR) spectroscopy has been studied for the confirmation of the presence of (M-O) bonding in the synthesized samples. Furthermore, the synthesized samples showed two frequency bands related to phonon vibrational stretching in both octahedral and tetrahedral lattice positions. The PL spectrum revealed the strong emission peaks in the ultraviolet to the visible region of all the synthesized samples. Raman spectroscopy showed the formation of four active modes due to the cubic spinel structure of all samples.Finally, the magnetic characteristics are calculated by using a vibrating sample magnetometer (VSM) showing ferrimagnetic and soft magnetic behavior of all the Magnesium ferrite samples. As the Cd and Zn co-doping in Mg ferrites was increased, the Hc was decreased. The magnetic studies revealed that the maximum Hc of 576 Oe and maximum saturation magnetization (Ms) appeared for the sample Cd0.50Zn0.50Mg0.25Fe1.75O4, carrying Cd/Zn in 50/50 ratio. It is envisaged that the novel preparation of Cd-Zn co-doped Magnesium ferrite would be suitable for several applications, for example, magnetic recording devices, actuators, high-density data storage devices sensors, and biomedical equipments.

Structural, Magnetic, and AC Measurements of Nanoferrites/Graphene Composites.

As a contribution to the graphene-based nanoferrite composites, this article is intended to present Mn, Co, and Co-Mn nanoferrites for the preparation and investigation of such samples. Nanoparticles of Co ferrite, Mn ferrite, and Co-Mn ferrite were chemically synthesized by the coprecipitation method. The composites of ferrite/graphene were made by incorporating weight ratios of 25% graphene to 75% ferrite. Various structural and characterizing investigations of ferrite samples and ferrite/graphene composites were performed, including XRD, EDX, SEM, VSM hysteresis loops, AC conductivity, and dielectric behavior. The investigations ensured the formation of the intended nanoferrite powders, each having a single-phase crystal structure with no undesired phases or elements. All samples exhibit a soft magnetic behavior. They show a semiconducting behavior of AC electrical conductivity as well. This was proved by the temperature dependence of the AC’s electrical conductivity. Whereas the dielectric function and loss tangent show an expected, well-explained behavior, the ferrite/graphene composite samples have lower saturation magnetization values, lower AC conductivity, and dielectric constant values than the pure ferrites but still have the same behavior trends as those of the pure ferrites. The values obtained may represent steps on developing new materials for expected applications, such as manufacturing supercapacitors and/or improved battery electrodes.

Microstructure and Properties of Additively Manufactured AlCoCr0.75Cu0.5FeNi Multicomponent Alloy: Controlling Magnetic Properties by Laser Powder Bed Fusion via Spinodal Decomposition.

A non-equiatomic AlCoCr0.75Cu0.5FeNi alloy has been identified as a potential high strength alloy, whose microstructure and consequently properties can be widely varied. In this research, the phase structure, hardness, and magnetic properties of AlCoCr0.75Cu0.5FeNi alloy fabricated by laser powder bed fusion (LPBF) are investigated. The results demonstrate that laser power, scanning speed, and volumetric energy density (VED) contribute to different aspects in the formation of microstructure thus introducing alterations in the properties. Despite the different input parameters studied, all the as-built specimens exhibit the body-centered cubic (BCC) phase structure, with the homogeneous elemental distribution at the micron scale. A microhardness of up to 604.6 ± 6.8 HV0.05 is achieved owing to the rapidly solidified microstructure. Soft magnetic behavior is determined in all as-printed samples. The saturation magnetization (Ms) is dependent on the degree of spinodal decomposition, i.e., the higher degree of decomposition into A2 and B2 structure results in a larger Ms. The results introduce the possibility to control the degree of spinodal decomposition and thus the degree of magnetization by altering the input parameters of the LPBF process. The disclosed application potentiality of LPBF could benefit the development of new functional materials.

Investigating the use of 3D printed soft magnetic PEEK‐based composite for space compliant electrical motors

AbstractElectric motors are ubiquitous on spacecraft and their smooth operation relies on the presence of naturally magnetic materials. The employment of conventional metal‐based magnets causes some inconveniences such as high values of specific gravity and the limited reproducibility of complicated geometries. The introduction of novel polymer‐based magnetic materials processed via additive manufacturing represents a brilliant answer to these needs. This paper describes the first‐time development of a polyether ether ketone‐magnetite (Fe3O4) soft magnetic composite. The material was prepared by adding 50 wt% magnetic microparticles to the polymeric matrix. The composite material was extruded in form of filaments and 3D printed via fused filament fabrication. The thermomechanical characterization demonstrated the stability of the material at both processing ad use temperatures, while the magnetic analysis reported a typical soft magnetic behavior with 25.7 A m2 kg−1 magnetization at saturation. The measured properties were employed as inputs for the finite element analysis of an axial flux brushless direct current electric motor, as a proof of concept. The simulation of the electromechanical behavior of the motor showed promising performance for the composite material, reaching the maximum deliverable torque of about 0.8 Nm (compliant to small power aerospace applications such as micro‐actuators and mini control moment gyroscopes) with weight savings up to 50%.

Effect of Annealing on the Magnetic Properties of FeCoNiCuNbSiB Soft Magnetic Alloys

A series of nanocrystalline soft magnetic alloys with nominal compositions of Fe66.8-xCo10NixCu0.8Nb2.9Si11.5B8 (x = 1–15 at%) were developed and studied. Effects of annealing on the soft magnetic properties, crystallization behavior, and domain structure were investigated. The alloys with higher Ni content were prone to exhibit stronger magnetic anisotropy. The Fe66.8Co10Ni10Cu0.8Nb2.9Si11.5B8 alloy exhibited excellent soft magnetic properties, including the low permeability of 2000, low coercivity of about 0.6 A/m, and low remanence of 2.4 mT, together with a temperature gap of 128 K between two crystallization onset temperatures. It has been found that the Ni content and the annealing process possess significant effects on the soft magnetic property of the nanocrystalline alloys. It shows that the developed Fe66.8Co10Ni10Cu0.8Nb2.9Si11.5B8 nanocrystalline alloy exhibits great potentials for applying in the field of common mode chokes or current transformers, due to its ability to resist the direct current.

Effect of Carboxymethyl Cellulose Concentration on Structural, Morphological and Magnetic Properties of Barium Hexaferrite: A Study Based on Sol-Gel Auto-Combustion Method

This study was intended to assess the role of carboxymethyl cellulose (CMC) as a chelating agent in the synthesis of barium hexaferrite (BaFe12O19:BaF). The effect of varying concentrations of CMC was studied via the sol-gel auto-combustion method following the requirements of green chemistry synthesis. The formation of BaF nanoparticles was confirmed using XRD, SEM, EDS, VSM, FTIR and UV-Vis-DRS techniques. The characterized XRD peak indicates the formation of good quality crystalline samples at 6% (w/v) of CMC concentration. SEM analysis suggested that the synthesized BaF is spherical, with sizes ranging from 10-15 nm. The M-H hysteresis loops obtained for the samples showed their soft and hard magnetic behaviour. With the increasing CMC concentration, magnetism becoming harder and an increase in the Ms value can be observed. The UV-Vis-DRS techniques revealed that the band gap energy of synthesized BaF increased with an increase in the concentration of CMC.

Magnetic, dielectric and structural properties of CoxZn(0.90-x)Al0.10Fe2O4 synthesized by sol–gel method with application as flexible microwave substrates for microstrip patch antenna

In this study, novel flexible microwave substrates based on CoxZn(0.90-x)Al0.10Fe2O4 nanopowder having an average grain size of 20 nm–26 nm were prepared using the sol–gel synthesis technique for microstrip patch antenna applications. At first there are three different molecular composition were chosen having the chemical formula of CoxZn(0.90-x)Al0.10Fe2O4 and specified as Co20, Co40 and Co60 for x = 20%, x = 40% and x = 60% respectively. Then the synthesized ferrites materials were characterized with XRD, FESEM, and VSM analysis, and single-phase spinel with high crystallinity were revealed. Besides, the dielectric and magnetic properties of the proposed Co–Zn ferrites samples were investigated for the affirmations of microwave applications. The values of dielectric constant εr and loss tangent (Tδ) are determined using dielectric assessment kit, and the obtained values are ranges from 3.5 to 4.5 for εr and 0.002 to 0.006 for Tδ for Co20, Co40, and Co60 respectively. Also, the magnetic permeability μr and magnetic loss tangent (Tδm) values are determined to form the predetermined scattering parameters S11 and S21 obtained from rectangular substrate pellets and the obtained values of μr and Tδm are ranges from 0.90 to 1.00 and 0.003 to 0.007 respectively. Finally, a modified diamond-shaped microstrip patch antenna is designed and fabricated on the proposed flexible substrates obtained from the synthesized Co–Zn ferrites nanopowders by mixing with PVA binder to validate their application in the S-band of microwave regime. The finite element method based computer simulation technology software is used to design the proposed microstrip patch antenna; furthermore, the simulated prototype is fabricated, and their reflections coefficients are measured for verification. The simulated and measured result of the proposed flexible antennas exhibits a maximum of 3 GHz bandwidth in between 2.5 and 5.5 GHz. Thus, the proposed materials offers tunable dielectric and magnetic properties with soft magnetic behaviors and easy to use where arbitrarily electromagnetic values are required. Moreover, these materilas also can be played significant role in flexible microwave field as low cost flexible substrates for compact flexible antennas, metamaterials, absorbers, and sensors applications etc.

Synthesis, thermodynamic analysis and magnetic study of novel ball- milled Co50Fe25Ta5Si5C15 glassy powders with high thermal stability

In this study, novel glassy Co–Fe–Ta–Si–C alloys were prepared by mechanical alloying, (MA) and the influence of annealing treatment and substitution of Fe for Co on glass-forming ability (GFA), thermal stability and magnetic properties were investigated. Quantitative X-ray diffraction (XRD) analysis by the Rietveld method showed that the new Co50Fe25Ta5Si5C15 powders have an enhanced glass formation rate, especially during the early milling stages compared to the Fe-free Co75Ta5Si5C15 alloy. In good agreement with the XRD measurements, the calculated PHSS thermodynamic parameter revealed that the GFA is notably increased for the new powder. Thermal analysis demonstrated a high thermal stability and a rather wide supercooled liquid region (SLR) of 51 K for the Co75Fe25Ta5Si5C15 glassy alloy. The milling process and subsequent annealing treatment remarkably improved the soft magnetic behavior of the Co75Fe25Ta5Si5C15 powder. The results indicated that the Co75Fe25Ta5Si5C15 glass exhibits a slightly higher coercivity (Hc) and a notably larger saturation magnetization (Ms) than the Co75Ta5Si5C15 alloy in the as-milled state. Furthermore, in the relaxed state, the new alloy possesses a markedly lower Hc of 0.96 kA/m and a higher Ms of 108 Am2/kg than Co75Ta5Si5C15 and large number of ssoft magnetic glasy powders prepared before. The influence of milling time and annealing temperature on the evolution of the magnetic properties were discussed in detail.

Effect of silica-coating on crystal structure and magnetic properties of metallic nickel particles

The development of a simple method that perfectly controls the oxidation and aggregation of metallic particles has been performed. In the present work, metallic nickel (Ni) particles were used as a control, and silica-coating of them was performed to control oxidation and aggregation of them. Metallic Ni particles with a particle size of 924.1 ± 315.7 nm were synthesized in water and exposed to air. Nickel(II) acetate tetrahydrate, hydrazine, and poly(sodium 4-styrenesulfonate) were used as the Ni source, reducing reagent, and stabilizer, respectively. Silica-coating of the metallic Ni particles was performed by adding tetraethylorthosilicate/(3-aminopropyl)triethoxysilane/ethanol solution to the metallic Ni particle colloid solution (Ni/SiO2). The uncoated metallic Ni particles and metallic Ni in the Ni/SiO2 particles began to be oxidized while annealing in air to form NiO at 400 and 500 °C, respectively; the oxidation of metallic Ni particles was controlled by the silica coating. The Ni/SiO2 particles prepared and annealed at 100–300 °C showed soft magnetic behavior, and the saturation magnetization of g-Ni was almost comparable to that of bulk metallic Ni. In addition, the Ni/SiO2 particles annealed even at 500 °C still had soft magnetic behavior, which also supported that the oxidation of metallic Ni particles was successfully controlled by the silica coating.

Characterization of nanostructured magnetic alloy based on Ni-Co-Mn produced by mechanical synthesis

Nanostructured Ni2MnCo alloy samples were prepared from pure elemental powders by Mechanical Alloying (MA) using a high-energy planetary ball mill. The obtained powders were characterized with XRD, SEM, laser diffraction granulometry and VSM techniques in order to study the microstructural, morphology, particle size distribution and magnetic properties as a function of milling time. The XRD patterns of as-milled powders revealed the formation of the main stage solid solution of Ni2MnCo with fcc structure phase after 24 h of MA. With increasing milling time from 0.5 hr to 50 hr, it is observed that the lattice parameter increases from 3.60 to 3.78 Å as well as an increase of microstrain from 0.17 to 0.41%, whereas the particle and crystallite size decreases down to 3.50 µm and 13 nm respectively. The mixture loses magnetization during the milling process due to the combined effects of crystallites size reduction and the dissolution of the antiferromagnetic compound (Mn) within the host lattice of the alloy. The very low values of the remanence ratio (Mr/Ms) ([1.2E-3, 1.7E-3]), as well as the very low values of the coercive field (≈ 1 Oe), were observed after 16 h of milling, which means that the alloy is magnetically saturated exhibiting a very soft magnetic behavior.

Design and development of Co35Cr5Fe20−xNi20+xTi20 High Entropy Alloy with excellent magnetic softness

The design and development of excellent soft magnetic materials are fascinating research areas in materials science. A series of Co35Cr5Fe20−xNi20+xTi20 (x = 5, 10, 15) High Entropy Alloys (HEAs) were synthesized through mechanical alloying (MA) technique and heat-treated at two different temperatures at 200 °C and 700 °C for 2 h. The XRD analysis confirmed that the HEAs comprised of face-centered cubic (fcc) phase and a minor fraction of an intermetallic R-phase at as-synthesized and annealed state. SEM-EDS observation confirmed the homogeneous compositional distribution and showed that after annealing at 700 °C, tiny spherical particles precipitated over the large grains. The synthesized HEAs showed soft magnetic behavior with low coercivity (12–16 Oe). However, the coercivity decreased more than five times to the initial value after the annealing at 700 °C. Co35Cr5Fe10Ni30Ti20 HEA annealed at 700 °C shows excellent soft magnetic properties with a high value of Ms (78.01 emu/g) and an extremely low value of Hc (1.7 Oe). The found value of the coercivity is the lowest value of the coercivity reported so far for the case of magnetic CoCrFeNiTi based HEAs. In addition, the present work provides a novel design strategy for the development of magnetic HEAs with excellent magnetic softness.

Tunable cationic distribution and structure-related magnetic and optical properties by Cr3+ substitution for Zn2+ in nanocrystalline Ni-Zn ferrites

We report a microwave-combustion synthesis and structure-related physical properties of Ni0.4Zn0.6−xCrxFe2O4 (0.0 ≤ x ≤ 0.6) nanocrystals in a study of effects by substitution among cations with different oxidation states, Cr3+ for Zn2+. High-quality nanocrystals with an average particle size of 26–33 nm and crystallite size ranged in 23–32 nm are revealed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Structural properties and cationic redistribution are studied by the XRD Rietveld analysis implying different preferences of Zn2+ and Cr3+ ions to occupy the tetrahedral and octahedral sites, respectively. Further characterization for the characteristic IR absorption bands, ionic valence states, chemical compositions and morphology have been performed by employing the Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and electron dispersive X-ray spectroscopy (SEM-EDX). XPS analysis indicates partial reduction of Fe3+ to Fe2+ and further confirms the estimated cationic distribution. UV–Vis absorbance measurements indicated a gradual decrease in the optical energy gap which implies the emergence of sub-band-gap energy levels by the Cr substitution. The magnetic properties were investigated by magnetization measurements showing highly soft magnetic behavior. The values and trend of the observed magnetic moment are consistent with the theoretically calculated magnetic moment based on cationic distributions estimated from the XRD and XPS. Ni-Zn-Cr spinel nanoferrites with soft magnetic properties, magnetization up to 106 emu/g and coercivity down to 70 Oe, tunable by cationic redistribution are introduced for high-frequency power applications.

Effect of sintering temperature on the synthesis of LiZnMnFe microwave ceramics with controllable electro/magnetic properties

Self-propagating high-temperature (SPHT) assisted method was successfully used to obtain soft magnetic ceramics based on the nanostructured powder of multicomponent lithium ferrite Li0·45Zn0·08Mn0·06Fe2·41O4. The influence of various temperature modes of sintering (900–1075 °C) on the microstructure, morphology, phase composition, and magnetic and electromagnetic properties of the initial powder and final ceramic products was analyzed in detail by methods of scanning electron microscopy, transmission electron microscopy, energy-dispersive and atomic absorption spectroscopy, thermogravimetry, calorimetry, X-ray diffractometry, induction magnetometry and measurement of electromagnetic parameters. It was shown that the particle size of the initial powder is 40 nm and depending on the sintering modes, it is possible to obtain lithium-zinc-manganese ferrite ceramics with an average grain size from 0.35 to 2.96 μm and porosity varying from 3.8 to 23.3%. The coercive force, residual induction, and saturation induction of the obtained samples were 51.3–816.6 A/m, 761.40–2131.30 G, and 1234.28–3431.71 G, respectively. It was found that the sample sintered at a temperature of 1075 °C for 8 h demonstrated the most pronounced soft magnetic behavior. The electromagnetic characteristics of the obtained samples also depended on the selected sintering mode and reached their maximum for ceramics sintered at a temperature of 1075 °C (ϵ’ = 11.52; ϵ” = 6.32⸱10−3; tan δϵ = 5.49⸱10−4; ΔH = 280 Oe; ΔHk = 1.87 Oe).

The Effects of Annealing After Equal Channel Angular Extrusion (ECAE) on Mechanical and Magnetic Properties of 49Fe-49Co-2V Alloy

Equal channel angular extrusion (ECAE) of 49Fe-49Co-2V, also known as Hiperco® 50A or Permendur-2V, greatly improves the strength and ductility of this alloy, while sacrificing soft magnetic performance. ECAE Hiperco specimens were subjected to post-ECAE annealing in order to improve soft magnetic properties. The microstructure, mechanical properties, and magnetic performance are summarized in this study. Annealing begins above 650 °C and a steep decline in yield strength is observed for heat treatments between 700 °C and 840 °C due to grain growth and the Hall–Petch effect, although some strength benefit is still observed in fully annealed ECAE material compared to conventionally processed bar. Soft magnetic properties were assessed through B–H hysteresis curves from which coercivity (Hc) values were extracted. Hc decreases rapidly with annealing above 650 °C as well, i.e., improved soft magnetic behavior. The observed trend is attributed to annealing and grain growth in this temperature regime, which facilitates magnetic domain wall movement. The coercivity vs grain size results generally follow the trend predicted in the literature. The magnetic behavior of annealed ECAE material compares favorably to conventional bar, possibly due to mild crystallographic texturing which enhances properties in the post-ECAE annealed material. Overall, this study highlights a definitive tradeoff between mechanical and magnetic properties brought about by post-ECAE annealing and grain growth.

Structural and magnetic properties of CoTi thin films deposited by magnetron sputtering method

ABSTRACT Co1–xTix (x = 0.3, 0.5 and 0.7) thin films were prepared on Si (100) substrate using DC-magnetron sputtering deposition technique. A structural phase transition occurs from hexagonal to cubic crystal structure when the Ti composition is above 30 percentage. The thickness of the films obtained from X-ray Reflectivity data is about 30 nm. The average particle size of the CoTi thin films was calculated using the Atomic Force Microscopy image. The Magneto-Optic Kerr Effect measurements suggest that only Co0.7Ti0.3 thin film exhibits soft magnetic behaviour whereas the other thin films have no magnetic properties because of small grain size and reduction of inter-grain exchange interaction. Co0.7Ti0.3 thin film has twofold magnetic anisotropy. The angle-dependent coercivity (H c) is numerically fitted with a two-phase model of magnetization reversal, which confirms the presence of magnetic anisotropy. The magnetization reversal occurs via coherent rotation of spins along the hard axis.

Soft-magnetic behavior of laser beam melted FeSi3 alloy with graded cross-section

Laser beam melting of rotors of soft-magnetic iron-silicon-based alloys with a graded cross-section promises a significant reduction of power losses during the operation of electric motors. In this work, graded cross-sections are designed with slits at different positions. The novel approach to design and implement the graded cross-section in laser beam melted FeSi3 alloy is presented. It is based on an interaction between initial slit thickness defined in the CAD-model and down skin parameters, i.e. laser power and the number of layers processed with down-skin parameters. This approach allows precisely to influence the resulting slit geometry, i.e. porous or continuous gaps filled with unmolten powder, and their thickness. The effect of both, the slit geometry and their position in ring specimens on the power losses during magnetization and demagnetization at different frequencies is analyzed and discussed. The obtained results reveal the significance of proper design and accurate control of the slit geometry in parts with graded cross-section. As it is shown, cross-sections with slits designed as continuous gaps result in a reduction of up to 43 % regarding the power losses in comparison to the bulk cross-section. Thus, the presented method for grading the cross-section can be relatively simply implemented in the design and manufacturing process of laser beam-melted rotors and allows to improve their performance in comparison with bulk AM rotors.