Development of advanced soft magnetic materials with improved properties for specific frequency applications.
Authors:   , Sota Angel 
Published: February 2025

Soft magnetic materials play a key role in the production of electrical and electronic devices. The need to produce new components with improved designs, enhanced properties and lower losses that result in lower emissions and high efficiency, is leading to the growth of research in the field of soft magnetic materials. However, the manufacture of improved soft magnetic devices is still in the early stage, thereby requiring of greater efforts. The development of improved
soft magnetic materials focuses on new compositions and new technologies. On the one hand, the current materials are well studied, and their advantages and disadvantages are known. Taking into account their properties, new compositions
are being designed to improve them, including better soft magnetic properties, higher temperature resistance, lower power losses, higher frequency of application, and lower manufacturing cost. On the other hand, new technologies
are being developed to manufacture electrical and electronic devices. In fact, the traditional fabrication methods, such as cold pressing, casting and rolling, are being replaced by these new technologies, which include additive manufacturing, FAST, and melt spinning. The framework of this thesis is based on the study of new fabrication routes and novel soft magnetic materials as a contribution to the fabrication of the future electrical and electronic devices. For this purpose, gas atomisation is used to produce soft magnetic powders. This technique is characterised by the production of powders with high sphericity and low surface defects, a high degree of control over the particle size and distribution of the powder, and a very high cooling rate (in the order of 106K/s). In addition, the high cooling rates achieved by this fabrication method provide a novel route for the production of amorphous powders, replacing the melt spinning technique currently used. The main advantage of producing amorphous materials in powder form is that they can be subsequently consolidated using a variety of technologies. This can result in different device shapes, as opposed to thin ribbons manufactured with melt spinning, which are limited in shape. The results of this work have been divided into three chapters. In addition, each chapter of results begins with a brief introduction to the state of the art, focusing on the topic of the chapter.
The first chapter of results focuses on soft magnetic materials for low frequency applications (50-60 Hz) such as low-frequency motors and transformers. In this case, laser-directed energy deposition (laser-DED) was used to consolidate Fe-3Si
(3 wt.% Si) and Fe49Co49V2 (known as supermendur or Hiperco 50A) powders. Both are compositions that are commonly used in industrial devices; however, they are typically produced by traditional techniques such as cold/hot rolling. Laser-DED additive manufacturing will therefore be analysed in terms of its advantages and disadvantages for the production of soft magnetic materials. The second and third chapters of this thesis look at medium and high frequency materials, where the so-called soft magnetic materials (SMCs) are produced. SMCs are made by consolidating soft magnetic powder previously coated with an insulating layer of a dielectric material, which can be polymeric, ceramic or a mixture of the two. Among these, the second chapter addresses the fabrication of iron phosphate-based SMCs consolidated by novel field assisted sintering technology (FAST). Iron phosphate (FexPyOz) is an iron-phosphorus oxide that can be easily produce by a wet-chemical method and which can be used to isolate Fe particles and thus produce SMCs. However, most studies have focused on cold pressing to consolidate the powder, which results in low densification and high residual stress due to the hard and brittle nature of the ceramic coating, which severely affects the soft magnetic properties. For this reason, FAST is proposed as a novel consolidation method for the production of this ceramic-based SMC. Finally, in the third chapter of results, amorphous-based SMCs are fabricated. Amorphous materials are characterised by high electrical resistivity and the absence of magnetocrystalline anisotropy, which results in very low power losses. These properties make amorphous powders particularly interesting for potential SMCs. In the manufacture of amorphous-based SMCs, cold pressing and epoxy resin are used for consolidation and coating, respectively. The main disadvantage of amorphous powders is their brittleness, which results in low compact density and therefore in lower saturation magnetisation and permeability. In this work, the mixing of particle sizes in a specific volume was used to increase the powder packaging and thus the compaction density.