Soft magnetic materials properties

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

Energy losses in soft magnetic materials arise due to both hysteresis and eddy currents, as described in the previous section. Eddy current losses can be reduced by increasing the electrical resistivity of the magnetic material. This is one reason why solid-solution iron-silicon alloys ( 4% Si) are used at power frequencies of around 60 Hz and why iron-nickel alloys are used at audio frequencies. Some magnetically soft ferrites (see Section 6.2.2.1) are very nearly electrical insulators and are thus immune to eddy current losses. Some common soft magnetic materials and their properties are listed in Table 6.19. Soft magnetic alloys are described further in Section 6.2.1.6. 

Table 6.19 Selected Properties of Some Soft Magnetic Materials...

Abstract The focus of this chapter is primarily directed towards nanocrystalline soft magnetic materials prepared by crystallization of amorphous precursors. The key elements involved in the development of this class of materials are three-fold (i) theoretical models for magnetic softness in nanostructures (ii) nanostructure-property relationships and (iii) nanostructural formation mechanisms. This chapter surveys recent research on these three areas with emphasis placed on the principles underlying alloy design in soft magnetic nanostructures. 

The soft magnetic properties of nanocrystalline soft-magnetic materials deteriorate drastically above the grain-decoupling temperature and thus,... 

Wang SX et al (2000) Sandwich films-properties of a new soft magnetic material. Nature 407 150-151... 

An important property of soft magnetic materials is the initial permeability. Its dependence on microstructure can be understood in terms of the Globus model. A calculation of the (relative) initial permeability (Globus, Duplex Guyot, 1971) leads to the following expression ... 

The physical basis of the use of Fe— Si alloys, commonly called silicon steels, as soft magnetic materials is the fact that both the magnetocrystalline anisotropy isTi and the magnetostriction parameters >.100 and Xm of Fe approach zero with increasing Si content (see Fig. 4.3-5a). The lower the magnitude of these two intrinsic magnetic properties is, the lower are the coercivity He and the AC magnetic losses The total losses ppe consist of the static hysteresis losses p y and the dynamic eddy current losses pw which may be subdivided into a classical p c and an anomalous p eddy current loss term. 

The fee phase in the Ni—Fe alloy system and the formation of the ordered NisFe phase provide a wide range of structural and magnetic properties for developing soft magnetic materials with specific characteristics for different applications. The phase diagram is shown in Sect. 3.1.5. Before amorphous and nanocrystalline soft magnetic alloys were introduced, the Ni—Fe materials... 

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