# Rapid Characterization Method for SMC Materials for a Preliminary Selection
## 1 Introduction  
Magnetic materials have been adopted in several sectors, from industrial, services, and IT to households, and in many applications and devices are the principal parts or components. In the case of hard magnetic materials, the general use concerns the flux generators and magnetic coupling; conversely, soft materials are adopted in the magnetic core of electrical motors and transformers [1, 2, 3]. In general, the main properties depend on the type of magnetic materials. For hard materials, the remanence (Br), the maximum magnetic energy density (BHmax) and the coercivity (Hc) represent the principal information. Conversely, for soft magnetic materials, the main properties' values are the permeability \(\mu\), saturated induction value, and iron losses. The permanent magnet materials are ferrites, AlNiCo, NdFeB, SmCo, bonded magnets, etc. ; commonly, the magnetic characterization is carried out through the use of a DC hysteresisgraph. Other techniques and equipment can be adopted for hard magnetic materials to measure magnetic characteristics and properties: vibrating sample magnetometers (VSM), pulsed-field magnetometers (only for magnets with very high electric resistivity), extraction magnetometers, SQUID magnetometers, to name a few. These arrangements allow a detailed measurement (high sensitivity) for different types and sizes of samples (flexible, liquid/organic, and nanoparticles). On the other hand, such measures require expensive equipment and a long experimental time, and their implementation is related to specific research centres. Soft magnetic materials are divided into several families: Iron-Silicon sheets, Nickel-Iron alloys (Permalloy, mu-metals), Iron-Cobalt-Vanadium alloys (Fe-Co-V, usually called Permendur), soft ferrites, amorphous magnetic materials, etc. The magnetic characterization depends typically on the type and dimensions of the sample. The Epstein frame is the most common technique applied to electrical steel sheets; this test can be performed for different values of frequency, but for high-frequency applications, toroidal magnetic tests are preferable. The single sheet tester (SST) is a faster solution but must be calibrated with both of the aforementioned test methods. The electronic conversion in different electrical and electromechanical devices allows operating in a vast range of frequencies. Additionally, the EMI filters and electronic passive components are affected by the selection of soft magnetic materials [4; 5; 6]. In this context, the laminated steel typically has high eddy current losses at medium-high frequencies; conversely, the amorphous and FeCo alloys are costly and need complex manufacturing processes, limiting their use. Due to the low saturation flux density, soft ferrites do not always represent the best solution for some devices. For these reasons, new soft magnetic materials have been introduced, named soft magnetic composites (SMC). Ferromagnetic particles are the core of SMC materials; such particles may be of different sizes, ranging from a few \(\upmu\)m to 0.5 mm, covered by an insulating layer. The layers are of organic or inorganic origin [7; 8; 9; 10]. In the case of inorganic insulating materials, different solutions are proposed and adopted based on silica, silicon particles, ferrite particles, amorphous powder, and metal oxides (Al\({}_{2}\)O\({}_{3}\), MnO, TiO\({}_{2}\), and others) [11; 12; 13; 14; 15; 16; 17; 18; 19]. Some of these solutions brought promising results but are still under study and development, mainly to resolve and improve mechanical performance. For the organic layer, a polymeric binder based on resins is most frequently adopted. In general, epoxy resin is preferable [20; 21; 22]; however, phenolic resins show excellent insulating and mechanical properties [23; 24; 25; 26; 27; 28]. Additionally, the silicone resin is a good solution for operating temperature until 500 \({}^{\circ}\)C [29; 30].