Deterioration Of Magnetic Properties Research Articles

Effect of replacing B by Zr in amorphous Co-Fe-Si-B soft magnetic alloys

Abstract

Crystallization mechanism and its correlation with structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys

Correlation of crystallization mechanism with the structural and soft magnetic properties of FeSiBPCu nanocrystalline alloys has been investigated on the basis of Johnson–Mehl–Avrami kinetic model, transmission electron microscopy, and extended random anisotropy model. Pre-existent α-Fe clusters in melt-spun alloys with a size much smaller than critical nucleus size crystallize at a steadily increasing nucleation rate owing to the chain effect of rising constituent fluctuation. This unique crystallization mechanism leads to the formation of fine and uniform nanocrystallites and therefore superior soft magnetic properties. In contrast, pre-existent α-Fe clusters with a size approximate to the critical nucleus size nucleate gradually at the initial stage of crystallization process driven by thermal activation over the energy barrier of nucleation, and pre-existent α-Fe nanocrystallites with a size larger than critical nucleus size grow directly at the initial stage of crystallization process. Grains formed at the initial stage enlarge further in the subsequent crystallization process, which gives rise to a continuous decrease of the nucleation rate and the deterioration of soft magnetic properties.

Development of stresses in grain-oriented electrical steel during laser treatment

Variation of magnetic losses in grain-oriented electrical steel subjected to single and multiple laser treatments has been investigated. It is shown that successive application of laser barriers in several passes through a laser unit leads to a deterioration of magnetic properties accompanied by a bending of the sample. The surface subjected to the laser treatment proves to be concave. The magnitude of stresses arising in the metal after each step of laser irradiation was calculated.

Bulk SmCo5/α-Fe nanocomposite permanent magnets fabricated by mould-free Joule-heating compaction

Bulk SmCo5/α-Fe nanocomposite magnets have been prepared using a Joule-heating compaction technique. Nearly fully dense bulk magnets are obtained by compacting the milled powders under a pressure of 2 GPa at temperatures above 400 °C. Structural analysis shows that the grain size of both the SmCo5 and the α-Fe phases is in the range of 10 to 15 nm when the compaction temperature is lower than 500 °C, which ensures effective interphase exchange coupling. A further increase in compaction temperature leads to significant grain growth and deterioration of magnetic properties. A maximum energy product of about 18.5 MGOe was obtained in the bulk SmCo5/α-Fe nanocomposite magnets, which is 90% higher than that of the single-phase counterpart prepared under the same conditions.

Insulating-coating flaws formed during laser processing of an electric anisotropic steel and their effects on magnetic properties

The effects of flaws in the insulating coating of an electric anisotropic steel, which are formed during its laser processing in accordance with the optimal technology used in industry, on the elastic tensile stresses induced in the metal by the coating and magnetic properties were investigated. It was shown that discontinuity of insulating coating at the location of laser-beam action does not lead to a decrease in elastic tensile stresses and deterioration of magnetic properties of steel.

Magnetic properties of nano-sized Co<SUB align="right">2FeSi

Nano–sized samples of Co2FeSi have been synthesised by mechanical alloying using a high energy ball mill. The average crystallite size shows a systematic decrease with milling time. M?ssbauer and DC magnetisation studies show that the Co2FeSi phase is formed at 9 h of milling and is optimised after 12 h of milling. Further milling results in the formation of a superparamagnetic phase with a corresponding deterioration in magnetic properties. A distribution in crystallite size is evident from the co–existence of superparamagnetic doublets with the magnetic hyperfine field in Mossbauer spectra. The presence of a large magnetically dead layer at the surface of the particles makes the value of saturation magnetisation less in the case of the 12 h sample as compared to the bulk. After 24 h of milling, the alloying process is complete but most of the particles of Co2FeSi are now superparamagnetic.

Influence of Ru/Ru–SiO 2 underlayers on the microstructure and magnetic properties of CoPt–SiO 2 perpendicular recording media

SiO 2 was doped into Ru underlayer to reduce the grain size of CoPt–SiO 2 perpendicular media. The effects of SiO 2 volume fraction and sputtering deposition pressure of Ru–SiO 2 underlayer on the microstructure and magnetic properties of CoPt–SiO 2 media were studied. Increasing SiO 2 volume fraction in Ru–SiO 2 layer decreased the grain sizes of Ru and CoPt. Adding 5% SiO 2 to Ru–SiO 2 layer increased the coercivity and enhanced the exchange decoupling and thermal stability of CoPt–SiO 2 layer. A further increase in SiO 2 volume fraction caused the deterioration of magnetic properties of CoPt–SiO 2 layer. Deposition of Ru–SiO 2 layer at 1.3 Pa resulted in a smaller activation volume and higher thermal stability of the CoPt–SiO 2 media than that deposited at 0.4 Pa.

Inspection of the residual curvature in an anisotropic electrical steel strip and reasons for its formation

The residual curvature of strips of anisotropic electrical steel (AES) is a defect of its geometry. This defect results in deterioration in magnetic properties of steel products in a transformer due to their stressed states. The residual curvature also leads to a slowdown in labor productivity during punching of items in automated lines. The main reason for the formation of a residual curvature in AES is attributed to a difference in elastic tensile stresses caused by the coating on different sides of a strip in the case of polythickness of the coating. The obtained minimal values of residual curvature are reached when the difference in the coating thickness on two sides of the strip is limited within 1 μm. The indicators of residual curvature are the bending radius (an absolute indicator) and the deviation of the free end of a vertically suspended specimen (a relative indicator). Laboratory techniques of determining the degree of bending and the methods of determining the residual curvature of the AES strip used at OOO VIZ-Stal’ are presented.

Soft Magnetic Properties of Nanostructured Vitroperm Alloy Powder Cores

Magnetic properties of amorphous and nanocrystalline samples have been experimentally investigated. Rapidly quenched ribbons of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (Vitroperm 800) were ball-milled and cryomilled to powder and warm-consolidated (at a pressure of 700 MPa) to get bulk compacts. It was found by investigating the influence of mechanical milling on the magnetic properties of powder samples prepared by milling that the alloy remains amorphous during the whole milling process. The frequency dependence of the coercivity and total core losses were studied. Investigation of the dc coercivity, magnetostriction, and electrical resistivity were done. Annealing at higher temperature causes a deterioration of dc soft magnetic properties. The higher coercivity of the as-prepared samples is mainly due to interfaces of the powder elements and internal stresses created by milling and consolidation that were decreased greatly after annealing. The frequency dependence of magnetic properties is also illustrated, and it is attributed mainly to the domain wall damping. The absolute values of losses and coercivity of Fe-based compacts are similar to that for Co-based compacts. We have prepared bulk samples in the form of the small cylinders with coercivity down to 13 A/m. These materials have more degrees of freedom for tailoring their magnetic properties due to their flexibility in shape and dimensions.

Preparation of ring-shaped composite bonded magnets with continuously controlled anisotropy distribution for internal space

We have already reported an advanced method for producing a radially-anisotropic rare earth composite bonded magnet with continuously controlled direction of anisotropy. The magnet has been applied to an inner rotor as a practical usage. In this study, the outstanding preparation method was adopted into the preparation of a magnet applied for an outer rotor. An optimized condition of extrusion and compaction at an elevated temperature could be obtained. In addition, a low pressure configuration to the ring-shaped magnet from plural preformed magnets was carried out, which had specific distribution of magnetic anisotropy for internal space for a small motor, by using self recoverability based on the viscous deformation without an alignment field. No deterioration of magnetic properties was detected through the process even if those magnets were miniaturized. Resultantly, the (BH)max of a ring-shaped magnet with the continuously controlled direction of magnetic anisotropy attained the value of 186 kJ/m3, and we obtained sine-wave magnetic anisotropy distribution, even if those magnets were miniaturized.

LTCC-Modules with Integrated Ferrite Layers—Strategies for Material Development and Co-Sintering

The integration of passive components (resistors, capacitors, inductors) into LTCC modules is a challenging task in multilayer ceramics technology. We report on multilayer assemblies consisting of combined layers of ferrite and dielectric LTCC tapes. Ni-Cu-Zn ferrites with maximum shrinkage at 900°C were processed to green tapes and laminated with dielectric LTCC tapes. Cosintering at 900°C led to multilayers with different defects such as incomplete densification of the ferrite layers, cracks, and warpage. Since ferrite tapes do not really allow compositional changes without deterioration of magnetic properties, the dielectric tape was modified with the following objectives: (i) matching of the shrinkage curves of dielectric and ferrite materials, (ii) adjusting the coefficients of thermal expansion to avoid cracking during cooling, and (iii) controlling of interface reactions. Using this concept we fabricated dense and defect-free multilayers consisting of dielectric and ferrite layers. However, compositional changes of the individual ferrite tapes require the development of a specific dielectric tape material with tailored properties.

Importance of punching and workability in non-oriented electrical steel sheets

In order to reduce energy loss in motors, the use of high-efficiency non-oriented electrical steel sheets and an optimal motor core design are important. It is also crucial to minimize the deterioration of magnetic properties during the motor core manufacturing process. Accordingly, this report evaluates the effects of cutting and clamping methods on the deterioration factors of motor cores. Magnetic properties are largely influenced by both cutting and clamping methods. While it is difficult to avoid cutting and clamping altogether, it is necessary to adopt suitable production conditions and minimize the deterioration involved.

Mathematical model for cutting effect on magnetic flux distribution near the cut edge of non-oriented electrical steels

Basic magnetic properties of non-oriented electrical steel sheets with different grain size and silicon content have different behaviour before and after cutting into strips. Cutting process causes a significant drop in flux density and deterioration of magnetic properties occurs over a region up to 10mm from close to the cut edge. Therefore some degraded regions are formed at each side of the cut. A new mathematical model was formed for the degree of deterioration on flux distribution near the cut edge. The variation of magnetic induction in the cutting region was given as a function of four different parameters depending on the material. The model also included the variation of these parameters with the grain size and silicon content. It is observed that the change in the parameters until 2.5% Si content is not significant, while it has a remarkable variation for them after 2.5% Si content and similar effect was found to be for grain size. The mathematical model gives the degree to which the magnetic properties of the region around the edge degrade after the cutting process. The calculated results of the model showed good agreements with the experimental results.

Effects of Alloying Element Balance and Micro-Alloying Elements on Magnetic Properties and Hot Ductility of PC Permalloy

The present study focused on improving the hot ductility and magnetic properties of PC Permalloy. An alloy with a chemical composition of 78.5 mass%Ni-4.3 mass%Mo-2.2 mass%Cu-0.47 mass%Mn-Fe exhibits the optimum permeability, with m0.005 of 411,200 and mm of 437,400. The P-value of the alloy was 3.43. Addition of Boron caused undesirable deterioration of magnetic properties, while the effects of Magnesium and Calcium on magnetic properties were small. Mill trials using a 50-ton electric furnace revealed that PC Permalloy with a composition of 78.6 mass%Ni-4.2 mass%Mo-2.1 mass%Cu-0.57 mass%Mn-14 ppmCa-4 ppmS-Fe exhibits extremely high permeability (i.e., m0.005, 233,000 to 499,000; mm, 368,000 to 568,000). High-permeability alloy sheets were obtained by controlling the P-value in the range of 3.45 to 3.49. The hot ductility of the alloy was markedly improved, and ingots and slabs were hot rolled without any corner cracks. [doi:10.2320/matertrans.MER2007235]

Nd–Fe–B thick films prepared at the high deposition rate of 90 µm/h

AbstractAfter a postannealing process, the magnetic properties of pulsed laser deposition (PLD)‐made Nd–Fe–B film magnets prepared at the deposition rate of 20–90 µm/h showed constant values, and the average values of Hc, Br and (BH)max were 1050 kA/m, 0.6 T, and 60 kJ/m3, respectively. The obtained results were comparable to those previously reported. In conclusion, it was found that a maximum deposition rate of 90 µm/h could be achieved without deterioration of magnetic and mechanical properties. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Spinodal decomposition in Fe–25Cr–12Co–1Si alloy under a 100 kOe magnetic field

Spinodal decomposition in Fe–25Cr–12Co–1Si alloy subjected to thermo-magnetic treatment under a 100 kOe magnetic field was investigated by transmission electron microscopy (TEM) and Mössbauer spectrometry. The high magnetic field was found to accelerate spinodal decomposition in the early stage, but restrain the coarsening process, which led to the formation of very fine modulated structures with small aspect ratio for the ferromagnetic α 1 phase. The abnormal deterioration of magnetic properties was mainly attributed to the decrease of shape anisotropy of ferromagnetic α 1 phase for the step-aged Fe–25Cr–12Co–1Si alloy.

Magnetic microstructure of NANOPERM‐type nanocrystalline alloys

AbstractControlled crystallization of amorphous NANOPERM‐type Fe76Mo8Cu1B15 alloy leads to the formation of crystalline grains of about 10 nm in size. The evolution of crystallization and its impact on the resulting magnetic properties is followed by nuclear and atomic based techniques of (subatomic) structural characterization comprising Mössbauer spectrometry, X‐ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, differential scanning calorimetry, and atomic force microscopy. The amount of nanocrystalline grains identified as bcc‐Fe rises with temperature of annealing and influences magnetic states of the original amorphous precursor. Results of structural characterization are correlated with magnetic data obtained from macroscopic measurements. In the samples with low contents of nanocrystallites, a deterioration of soft magnetic properties is observed. A very good soft magnetic behaviour is regained, however, towards the end of the primary crystallization process. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Magnetic properties of extremely small Nd-Fe-B sintered magnets

Magnetic properties of small Nd-Fe-B sintered magnets were investigated. Thickness of surface damaged layer, which shows low coercivity and causes the deterioration in magnetic properties, was found to be comparable to mean grain size of sintered bodies. Magnets with small grains of around 5 /spl mu/m showed rather higher magnetic performance after machining into small pieces with a surface area/volume ratio of 20-35 mm/sup -1/. Chemical etching with a nitric acid solution was effective in partial recovery of magnetic properties through bringing slightly higher coercivity of surface grains. Heat treatment at higher temperatures than the melting point of Nd-rich phase and subsequent aging enhanced the coercivity of surface grains. Coating with powders of Dy/sub 2/O/sub 3/, DyF/sub 3/, or TbF/sub 3/ before the heat treatment resulted in a great enhancement in coercivity without significant reduction in remanence.

Precipitation and high temperature magnetic properties of FeCo-based alloys

The microstructure and high temperature magnetic properties of Fe–Co–2V and Fe–Co–2V–0.3Nb alloys have been investigated. Aging at 600 °C, γ2 phases precipitate whose size and volume fraction increase with increasing aging time. A roughly linear relationship between magnetic coercivity Hc and volume fraction of the γ2 precipitates was observed. Addition of Nb facilitates nucleation and growth of the γ2 precipitates, resulting in a dramatic deterioration of soft magnetic properties of the alloys. A pinning effect of the γ2 precipitates on the magnetic domain wall has been observed by Lorenz electron microscopy.

Effect of inhomogeneous intergranular phases on magnetic properties of nanocomposite magnets

Micromagnetic calculation was carried out for investigating the relationship between nanostructure and magnetic properties of Nd–Fe–B-based nanocomposite magnets in consideration of imperfect nanostructures. The calculation predicted that nonmagnetic intergranular layers and inhomogeneous intergrain exchange interaction result in a deterioration of magnetic properties. Particularly, the deterioration is significant for a magnet with a grain size larger than the optimal one, and the simulated demagnetization curve, assuming an imperfect nanostructure, agreed roughly with that measured. Therefore, a further improvement in magnetic properties is expected by achieving a fine and homogeneous nanostructure.