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Efficient and cost-effective soft magnetic materials (SMMs) are essential for accelerating the adoption of electric vehicles and the sustainable growth of renewable electricity. While amorphous and nanocrystalline SMMs offer remarkably low magnetic losses, their poor mechanical properties, limited availability in size and shape (particularly ribbon widths), and high cost prevent them from widespread industrial application. Here, we show that ductile Fe-6.5%Si 2-D flakes could be used as building blocks for making high performance bulk SMMs. This approach bypasses the brittleness problem and creates a new morphology and a new fabrication method for the SMMs with improved energy efficiency and lower processing cost. Ductile Fe-6.5%Si flakes are mass-produced by melt spinning and are then consolidated to bulk SMMs with a brick-wall type of structure. The novel process introduces anisotropic electrical and magnetic properties and enables near net shape processing. Resulting Fe-6.5%Si thin sheets display low iron loss (W10/400 = 6.1 W/kg) and high permeability (µ r = 28,000), which are comparable to the current state of the art high silicon steel. CaF 2 coating reduces the iron losses for thick Fe-6.5%Si parts. Polymer coated Fe-6.5%Si flake cores show potential for high power inductors with greater permeability and lower losses than traditional powder cores. Image, graphical abstract [ABSTRACT FROM AUTHOR]

MnBi is an attractive rare-earth-free permanent magnetic material due to its low materials cost, high magnetocrystalline anisotropy (1.6 × 106 J m−3), and good magnetization (81 emu g−1) at room temperature. Although the theoretical maximum energy product (BH) max of 20 MGOe is lower than that of NdFeB-based magnets, the low temperature phase (LTP) of MnBi has a positive temperature coefficient of coercivity, up to 200 °C, which makes it a potential candidate for high temperature applications such as permanent magnet motors. However, the oxygen sensitivity of the MnBi compound and the peritectic reaction between Mn and Bi make it difficult to synthesize into a material with high purity. This challenge is partly offset by adding excess Mn to the alloy, with composition close to Mn 55 Bi 45 resulting in the highest saturation magnetization after common processing techniques such as arc melting, casting, melt spinning, and ball milling. Here we report a systematic process which reduces the amount of excessive Mn, while simultaneously providing a large saturation magnetization (M S) of 79 emu g−1 at 300 K in the annealed Mn 52 Bi 48 ribbons. We also report excellent magnetic properties in the ball powders, resulting in 0.5–5 µm particles with M S of 75.5 emu g−1, coercivity H ci of 10.8 kOe, and (BH) max of 13 MGOe using 9 T applied field at 300 K. A secondary annealing treatment on various ball milled powders increased H ci by up to 21%, and also resulted in an increase in M S up to 78.8 emu g−1. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Fe-6.5wt%Si steel surpasses the current extensively used Fe-3.2wt%Si steel in lower iron loss, higher permeability, and near zero magnetostriction. As a cost effective soft magnetic material, Fe-6.5wt%Si may find applications in motors, transformers, and electronic components. However, the brittleness of the alloy poses processing challenges. The brittleness in Fe-6.5wt%Si is attributed to the formation of ordered phases. Evaluation of the amount of ordered phases is important for the research and development of Fe-6.5wt%Si. This paper aims to find effective ways to evaluate the ordering degree through a comparison of various characterization techniques. In order to tune the ordering degree, various speeds were used to prepare Fe-6.5wt%Si samples via melt spinning. The varying wheel speed changes the cooling rate, which was confirmed by thermal imaging. In addition to the widely used TEM and normal theta-2theta X-ray diffraction methods, two quantitative methods were adopted for this Fe-6.5wt%Si system to study the ordering degree. One method is based on rotating crystal XRD technique, and the other is magnetic thermal analysis technique. These two methods effectively quantified the varying degree of ordering presented in the samples and were deemed more suitable than the TEM, normal theta-2theta XRD methods for Fe-Si due to their ease of sample preparation and short turn-around time. Image 1 • New cooling rates data on melt spun Fe-6.5%Si ribbons. • Varying degree of order achieved on the Fe-6.5%Si ribbons. • New techniques charactering Fe-6.5%Si ordering proposed. [ABSTRACT FROM AUTHOR]

Compared to the widely used Fe-3.2wt%Si steel, Fe-6.5wt%Si has superior electric and magnetic properties, including higher electrical resistivity, lower iron loss, higher permeability, and near zero magnetostriction. However, Fe-6.5wt%Si sheet is difficult to produce using traditional manufacturing processes as the high silicon content favors the formation of ordered phases that embrittle the material. Fortunately, these ordered phases can be suppressed if the alloy is cooled fast enough from a high temperature kinetically trapping the disordered solid solution or amorphous state. Planar flow casting is known for its rapid solidification rate. In order to consider it as a viable method to manufacture ductile Fe-6.5wt%Si sheets, the effect of cooling rate on physical properties of Fe-6.5wt%Si alloy are systematically investigated. In this work, various cooling rates are achieved by changing melt-spin wheel speeds, which significantly affect the solidification temperature profile and have profound effects on ordering, microstructures, textures, hardness, and magnetic properties. High cooling rates result in refined grains, reduced ordering, enhanced <100> out of the plane texture, decreased hardness, and increased coercivity. This study shows a critical cooling rate at ~1.7 × 105 K/s, corresponding to a tangential wheel speed of 5-7 m/s, below which the hardness significantly increases in agreement with the sudden increase of the ordered phases that causes the material embrittlement. Image, graphical abstract [ABSTRACT FROM AUTHOR]