Improvement Of Soft Magnetic Properties Research Articles

Improvement of soft magnetic properties of a Nanoperm-type Fe-Hf-B nanocrystalline alloy upon surface crystallization inhibition by Cu addition

Nanoperm-type alloy ribbons suffer from surface crystallization during melt spinning, which degrades their magnetic properties after annealing and limits their commercial application. Here, we investigate the effects of Cu addition on the structure and magnetic properties of a surface-textured Fe87-xHf5B8Cux alloy. Adding Cu (1 ≤ x ≤ 2) removes the surface coarse grains in the free surface of the melt-spun precursor, while induces the precipitation of large amounts of the α-Fe nanoparticles with ∼3 nm in size, which contributes a homogeneous ultrafine structure and improved magnetic softness after annealing. The grain size, coercivity, saturation magnetic flux density, and effective permeability at 1 kHz of the Fe86Hf5B8Cu1 nanocrystalline alloy are 13.3 nm, 6.6 A/m, 1.68 T, and 23000, respectively, whereas these are 16.0 nm, 16.8 A/m, 1.70 T, and 15000, respectively, for the Fe87Hf5B8 alloy. The Cu-improved effect is mainly attributed that Cu induces heterogeneous nucleation of the α-Fe phase to strengthen the competitive growth among grains.

Improvement in soft magnetic properties of thin bilayer ribbons using magnetoelastic effect

We have prepared Fe-Ni-system bilayer ribbons with different magnetostriction (compositions) and investigated the improvement of soft magnetic properties using the magnetoelastic effect. A toroidal core with D = 10 mm was made from the Fe6Ni94/Fe56Ni44 bilayer ribbon, and the B-H loop of the core was measured. The shape of the hysteresis loop dramatically changed depending on the inner layer (inner magnetic phase). This result indicates that the direction of the anisotropy induced by bending stress was changed depending on the inner layer. The slope of the B-H loop and coercivity reduced when the Fe56Ni44 layer was on the inner side. From the experimental results, we found that domain rotation was dominant for the magnetization process. Consequently, the increase in the coercivity over frequency could be suppressed by controlling the magnetization process. From these results, we found that a thin bilayer ribbon with positive and negative magnetostriction constant is an attractive material for reducing iron losses under high frequency.

Improvement of soft magnetic properties of a Fe84Nb7B9 nanocrystalline alloy by synergistic substitution of P and Hf

A strategy of similar elements synergistic substitution was implemented to enhance the amorphous forming ability (AFA), thermal stability, and soft magnetic properties of Fe-Nb-B nanocrystalline alloys. Substitution of B by 2–6 at.% P in a Fe84Nb7B9 alloy increases the AFA and transforms the partially crystallized melt-spun ribbon into a fully amorphous structure. 2–4 at.% P lowers the grain size and enhances the size uniformity and volume fraction of the α-Fe phase in the annealed alloys, thus decreasing coercivity (Hc) from 20.0 to 12.8 A/m and increasing saturation magnetic flux density (Bs) from 1.50 to 1.57 T, whereas 6 at.% P coarsens the α-Fe grains and reduced the magnetic softness. Subsequent replacement of Nb by 2–3.5 at.% Hf increases the thermal stability of a Fe84Nb7B5P4 amorphous alloy, and further refines the α-Fe grains and improves the structural uniformity of the nanocrystalline alloys, thereby enhancing the soft magnetic properties and enlarging optimum annealing temperature window (ΔToa). The Fe84Nb3.5Hf3.5B5P4 nanocrystalline alloy with an average grain size of 9 nm exhibits a low Hc of 11.2 A/m, high Bs of 1.55 T, and wide ΔToa of 90 K. The mechanism of P and Hf substitutions affecting the structure and magnetic properties of the Fe84(Nb, Hf)7(B, P)9 nanocrystalline alloys was discussed in terms of primary crystallization behavior regulation.

Effects of heat treatment in air on soft magnetic properties of FeCoSiBPC amorphous core

The oxidation behavior and soft magnetic properties of industrially prepared Fe80Co3Si3B10P1C3 amorphous cores were investigated under heat treatment in air. Results indicate that the FeCoSiBPC amorphous core heat-treated in air can obtain higher permeability (μi) and maximum saturation magnetic induction (Bm) than that annealed in vacuum. The improvement of soft magnetic properties originates from the formation of a Co-rich layer between the oxide layer and the amorphous substrate after the selective oxidation of Fe. The core loss (Pcm) of the amorphous cores decreases after annealing at 280 ℃ in air for 30 min, and increases with the annealing time extend to 60 min. The Pcm of the samples treated in air is inferior to that of the ones annealed in vacuum for 30 min. The variation of Pcm can be explained by the thinning of the amorphous substrate based on the Gyorgy's model and simple models of domain wall pinning.

Improvement of soft magnetic properties and in-plane uniaxial magnetic anisotropy in FeCoAlO films fabricated by asymmetric targets

Improvement of soft magnetic properties and in-plane uniaxial magnetic anisotropy in FeCoAlO films fabricated by asymmetric targets

Nanoscale structural heterogeneity perspective on the ameliorated magnetic properties of a Fe-based amorphous alloy with decreasing cooling rate

Despite that the nanoscale structural heterogeneity of amorphous alloys has been confirmed by advanced experimental observations and theoretical simulations, the underlying link between the structural heterogeneity and magnetic properties remains poorly known. In this work, the effect of cooling rate on the nanoscale structural heterogeneity and magnetic properties of Fe80Si9B11 amorphous ribbons (Fe-Si-BAR) was studied by atomic force microscopy and Mössbauer spectroscopy. The results show that the degeneration of nanoscale structural heterogeneity substantially induces an improvement in soft magnetic properties with decreasing cooling rate. Specifically, the volume fraction of flow units reduces significantly with the decrease of cooling rate, and some of the flow units annihilate and transform to the ideal elastic matrix. The structural densification and reduction of the number density of quasidislocation dipole result in an enhancement in ferromagnetic exchange interaction and weakening of magnetic anisotropy. Therefore, the saturation magnetic flux density increases and coercivity decreases with reducing cooling rate. Our results provide new insight into understanding the structural mechanism in the ameliorated magnetic properties of Fe-based amorphous alloys with decreasing cooling rate.

Optimization of crystallization, microstructure and soft magnetic properties of (Fe0.83B0.11Si0.02P0.03C0.01)99.5Cu0.5 alloy by rapid annealing

A (Fe0.83B0.11Si0.02P0.03C0.01)99.5Cu0.5 glass former was formulated based on Fe83B11Si2P3C1 alloy and a new rapid annealing method was employed to investigate both the temperature and time effect on the improvement of soft magnetic properties of the amorphous alloy ribbon. The results show that the interval between the first and second crystallization temperature is enlarged by Cu addition. There exists an optimal annealing time corresponding to the optimal Bs and Hc for the ribbon annealed at each temperature. The maximum Bs up to 1.74 T and the minimum Hc of 4.9 A/m were obtained for the ribbon annealed at 426 °C for 150 s. The grain number density of precipitated α-Fe(Si) is the main factor in determining the Bs. Compared to other nanocrystalline alloys with similar Fe content, the present alloy ribbon annealed by the new method shows a higher Bs and a lowest Hc, which makes it a promising soft magnetic material used in the field of electrical and electronic industries.

Twin Roll Casting and Secondary Cooling of 6.0 wt.% Silicon Steel

Iron–silicon alloys with up to 6.5 wt.% Si offer an improvement of soft magnetic properties in electrical steels compared to conventional electrical steel grades. However, steels with high Si contents are very brittle and cannot be produced by cold rolling. In addition to solid solution hardening, it is assumed that the B2- and DO3-superlattice structures are responsible for the poor cold workability. In this work, two cast strips with 6.0 wt.% Si were successfully produced by the twin roll strip casting process and cooled differently by secondary cooling. The aim of the different cooling strategies was to suppress the formation of the embrittling superlattice structures and thus enable further processing by cold rolling. A comprehensive material characterization allows for the understanding of the influence of casting parameters and cooling strategies on segregation, microstructure and superlattice structure. The results show that both cooling strategies are not sufficient to prevent the formation of B2- and DO3-structures. Although the dark field images show a condition which is far from equilibrium, the achieved condition is not sufficient to ensure cold processing of the material.

Improvement of SMPs in Fe-Si-B-P-C-Cu-Nb alloys via harmonizing P and B

The effect of P content on crystallization behavior, microstructure, magnetic domain structure, and magnetic properties of Fe81.5Si3B13-xP0.5+xC0.2Cu0.8Nb1 (x = 0, 1, 2, and 3 at. %) alloys have been investigated. The results of XRD and DSC suggest that the moderate increase in P content improves the amorphous forming ability (AFA) of the alloys and enlarges the temperature interval to 153 K between two crystallization peaks. The activation energy indicates that the relative increase in P content prompts the precipitation of α-Fe phase and improves the thermal stability. Through optimal annealing treatments, the nanocrystalline alloy with x = 3 exhibits excellent soft magnetic properties (SMPs), including high Bs above 1.65 T, high µe about 19000, low Hc below 3 A/m and P10/50 around 0.12 W/kg. The microstructures of the alloys annealed at optimal conditions were detected via XRD and TEM, the results of which show that harmonizing P and B not only refines grains but enhances the nanostructure homogeneity. The investigation with magneto-optical Kerr microscopy reveals the magnetic domain evolution of x = 3 alloy including stress domain removing, domain differentiating and broadening process.

Structure and magnetic properties of milled maraging steel powders

We demonstrate that high-energy ball milling of gas-atomized maraging steel powder followed by suitable thermal-treatment produces nanocrystalline maraging steel powders having improved magnetic properties, compared to the gas-atomized powders. Milling for five to eighthours formed powders comprised of, primarily, nanocrystalline martensite. The saturation magnetization (MS) of the milled powders ranged between ~164 Am2/kg and ~169 Am2/kg, while the intrinsic coercivity (HCI) ranged between ~4.9kA/m and ~6.7kA/m. At sub-ambient temperatures, from 60K to 390K, both MS and HCI decremented with the increment in temperature. The thermomagnetic behavior of the milled powders was somewhat reversible. At supra-ambient temperatures (500K–900K), both MS and HCI monotonically decreased with the increase in temperature. The thermally treated powders constituted nanocrystalline martensite and exhibited increment (by ~6%) in MS and decrement (~nearly halved) in HCI compared to the milled powder, i.e., the powders exhibited improvement in soft-magnetic properties.

Effect of Cu on microstructure, magnetic properties of antiperovskite nitrides CuxNFe4−x

For soft magnetic materials, especially new intermetallic compounds, some good soft magnetic properties, such as high permeability, low power loss, as well as superior DC-bias properties, will determine their prospects for application. In this paper, we report soft magnetic properties of CuxNFe4−x, prepared by a new synthetic method. Although the saturation magnetization of the samples is slightly lower than that of Fe4N due to Cu doping, various other experimental results clearly provide evidence that the Fe substitution by Cu leads to the optimization and improvement of soft magnetic properties in Fe4N. With increasing Cu content, the permeability increases and power loss reduces from 1064.5 mW/cm3 for x = 0.1 to 679 mW/cm3 for x = 0.5 at H = 8 A/m, f = 1000 kHz. Additionally, the value of DC-bias (μH/μH=0) rises above 82% at H = 100 Oe, implying a superior DC-bias properties. More importantly, with the increases of x content, the value of μH/μH=0 increases and reaches 87% for sample x = 0.5 at H = 100 Oe. The improvement of soft magnetic properties of the Fe-based antiperovskite CuxNFe4−x is encouraging for future applications as functional materials.

Significant improvement of soft magnetic properties for Fe-based nanocrystalline alloys by inhibiting surface crystallization via a magnetic field assisted melt-spinning process

Abstract Fe-based soft-magnetic amorphous and nanocrystalline ribbons made with a single-side fast-cooling process always suffer from the surface crystallization which deteriorates the magnetic properties and inhibits the wide applications. In this study, a static magnetic field assisted melt-spinning process was employed to prepare the typical Fe84.75Si2B9P3C0.5Cu0.75 alloy ribbon with an attractive application prospect. According to the comparative investigations of the crystallization behavior, structural evolution process and magnetic properties, it is found that the applied magnetic field can effectively inhibit the formation of compound phases and decrease the size of textured α-Fe grains in the surface layer of the as-spun ribbon. The Fe84.75Si2B9P3C0.5Cu0.75 samples made with low purity raw materials and under an optimal field exhibit superior magnetic properties, including a high saturation magnetization (Bs) over 1.82 T, low coercivity (Hc) of 8.5 A/m, high permeability (μ) of 2.76 × 104 at 1 kHz and much lower losses, after nanocrystallization by annealing. The apparent effect of the applied magnetic field was discussed from the disturbance of a Lorentz force of the fast-moving molten alloy and a magnetic force of preformed grains in a magnetic field during the melt-spinning process. These results provide a novel solution of surface crystallization and an effective route for improving magnetic properties of Fe-based amorphous and nanocrystalline alloy ribbons.

Improvement of soft magnetic properties of FeSiBPNb amorphous powder cores by addition of FeSi powder

The effect of FeSi powder with volume fraction of 0–40% on the soft magnetic properties of the FeSiBPNb amorphous powder cores has been systematically investigated in this study. The results shows that the amorphous magnetic powder core mixed with 10% FeSi powders in volume fraction exhibits superior DC-bias properties, constant permeability, low core loss up to a higher frequency range, and excellent soft magnetic properties after appropriate heating treatment. The DC-bias properties of the present amorphous magnetic cores decrease by only 20% as the external field increases to 100 Oe. Meanwhile, it also exhibits a high permeability of 60 at 10 MHz and a low core loss of 159 W/kg at Bm = 0.1 T and f = 50 kHz. The present Fe-based amorphous magnetic powder cores mixed FeSi powders with superior DC-bias properties are a potential candidate for a variety of industrial applications.

Improvement of soft magnetic properties of Fe0.7Nb0.1Zr0.1Ti0.1 amorphous alloy: A kinetic study approach

In this paper, the crystallization kinetic of amorphous Fe0.7Nb0.1Zr0.1Ti0.1 was studied by differential thermal analysis to produce an appropriate amorphous/nanocrystalline microstructure for improving the soft magnetic properties. Amorphous Fe0.7Nb0.1Zr0.1Ti0.1 alloy without metalloids was prepared by mechanical alloying of pure elements. The results showed that Johnson-Mehl-Avrami model was able to explain the crystallization kinetic of products as: dαdt=βdαdT=4.86×109exp−186776RT1−α−ln1−α0.24. Moreover, volume diffusion control with three dimensional growth of the nuclei was the predominant mechanism of crystallization. The simulation results confirmed that by employment of kinetic model, it was possible to control the microstructure as combination of amorphous/crystalline phases and enhance the saturation magnetization from 59 to 142 A·m2/kg and reduce the coercivity from 2.05 to 0.14 kA/m by controlling of crystallization progress at specific predefined α value.

Significant improvement of soft magnetic properties for Fe(Co)BPSiC amorphous alloys by magnetic field annealing

Longitudinal field annealing (FA) is used to improve the soft magnetic properties (SMPs) of Fe83-xCoxB11P3Si2C1 (x = 0–20) amorphous alloys with high Bs of 1.65–1.76 T. These amorphous ribbons after FA exhibit pronouncedly improved SMPs, including low coercivity of 1.0–2.3 A/m and high permeability of 6.6–13 × 103 at 1 kHz. In comparison with normal annealing (NA), FA is found to be an effective process in improving the SMPs for all amorphous alloys. While NA is only effective for the alloys with Tc lower than the onset temperature of the crystallization (Tx1). It is also found that FA can change the domain sensitive direction from transversal to along the ribbon axis, and unify the easy magnetization direction. This mechanistically explains the positive effects of applied field on SMPs and structure relaxation. This paper will give a better understanding of relaxation effect on SMPs and a prospective view in formulating heat-treatment process of the thin ribbons fabricated by using a single roller melt spinning process.

Effect of an annealing on magnetic properties of Fe-Ni films electroplated in citric-acid-based plating baths

We have already reported Fe-Ni films with good soft magnetic properties prepared by using an electroplating method. In the present study, we employed an annealing for further improvement in soft magnetic properties of the electroplated Fe-Ni films. The annealing reduces the coercivity of the films, and the reduction rate of the coercivity depended on the Cl- ion concentration in the bath. The Fe22Ni78 films prepared in the plating bath with high Cl- ion concentration showed large reduction rate of the coercivity, and we found that the annealing is more effective for high Cl- ion concentration bath since much lower coercivity value can be obtained compared with that for low Cl- ion concentration one.

The effects of field annealing on the magnetic properties of FeSiB amorphous powder cores

The effects of transverse magnetic field annealing on the magnetic properties of Fe78Si9B13 amorphous powder cores were investigated. The cores annealed at 400°C under an external transverse magnetic field of 0.5 T show an enhanced and stable effective permeability of 90 in the high frequency range up to 2MHz. Meanwhile, the permeability was improved by about 5% and the core loss was decreased by about 10% compared to the core with zero field annealing, which is attributed to the relief of internal stress and the variation of domain structure. It also shows superior DC bias property with a “percent permeability” of 70% at an external field of 100Oe. Transverse magnetic field annealing is an effective way to improve the soft magnetic properties of the amorphous powder cores. The improvement of soft magnetic properties of the Fe-based amorphous powder cores is encouraging for future applications as functional materials.

Structural and magnetic properties of nanocrystalline Fe–Co–Si alloy powders produced by mechanical alloying

We report the structural and magnetic properties of nanocrystalline Fe100−x−yCoySix (x = 10, 15, y = 0–20) alloy powders prepared by mechanical alloying process in a planetary ball mill. All the as-milled powders exhibit non-equilibrium α-Fe(Co,Si) solid solution with average crystallite size of 7–11 nm. The lattice constant increases initially up to 10 at.% Co and then decreases with further increase in Co content due to delay in dissolution of Co into Fe lattice by the introduction of more Si. The variations of structural parameters such as average crystallite size, dislocation density and fraction of grain boundary as a function of Co content show good correlations among them. The substitution of Co in Fe100−x−yCoySix alloy powder increases both saturation magnetization and coercivity due to atomic ordering which induce additional magnetic anisotropy. Thermomagnetization studies reveal that Curie temperature (TC) increases at a rate of 4 K per at.% Co for Co content up to 10 at.% and the rate of increase in TC reduces to 1.4 K per at.% Co for higher Co addition. The variation of structural and magnetic parameters reveals a strong dependence on the composition of Fe–Co–Si alloy. The observed results show the improvement in soft magnetic properties of nanocrystalline Fe–Co–Si alloy powders by proper substitution of Co and Si for Fe.

Magnetic properties and loss separation in Fe76−xAgxNb2Si13B9 amorphous alloys

Abstract Some selected properties (magnetic, plastic, elastic) in amorphous Fe 76− x Ag x Nb 2 Si 13 B 9 ( x = 0.5, 0.75, 1.0) alloys, obtained by melt spinning technique, are presented and discussed in detail. It was shown that a suitable heat treatment of the as quenched samples (i.e. the optimization annealing) leads to a significant improvement of soft magnetic properties (permeability increases at least 10 times). The observed effect is attributed to formation of the so-called relaxed amorphous phase free of iron nanograins. Special attention is paid for loss separation into different components: hysteresis loss, eddy-current loss and residual loss. The latter effect can be attributed to diffusion of free volume and practically disappear after the optimization annealing.

Preparation of Quasi‐Ternary Fe‐P‐C Bulk Metallic Glass Using Industrial Raw Materials with the Help of Fluxing Technique

Bulk quasi‐ternary Fe80P13C7 (the real composition is Fe79.4Si1.0P12.8C6.8) glassy rod alloy with the maximum diameter of 1.0 mm was prepared by combining fluxing treatment and J‐quenching technique using industrial cast iron and Fe–P alloys as raw materials. The result shows that the present Fe‐based bulk metallic glass (BMG) exhibits good soft magnetic and mechanical properties with a high saturation magnetization of 1.43 T, a low coercivity of 7.2 A m−1 (for as‐cast melt‐spun glassy ribbon) and a high fracture strength over 2.75 GPa. The effects of fluxing treatment on the glass‐forming ability (GFA), thermal stability, and magnetic properties of the present Fe‐based amorphous alloy fabricated using industrial raw materials have also been investigated. It is indicated that the GFA of the present Fe‐based alloy prepared using industrial raw materials is greatly improved through fluxing treatment, which should be attributed to the effective elimination of the impurities in alloy. In addition, soft magnetic properties of the present Fe‐based amorphous alloy can be significantly improved by fluxing treatment, and the melt‐spun glassy ribbon obtained from the fluxed mother alloy has a lower coercivity and higher Curie temperature compared with the melt‐spun glassy ribbon obtained from un‐fluxed mother alloy. The improvement in soft magnetic properties should be attributed to the purification of the master alloy through fluxing treatment, which results in more uniform atomic arrangement structure in the produced amorphous alloy.