Soft magnet

Fig. 3. An overview of atomistic mechanisms involved in electroceramic components and the corresponding uses (a) ferroelectric domains capacitors and piezoelectrics, PTC thermistors (b) electronic conduction NTC thermistor (c) insulators and substrates (d) surface conduction humidity sensors (e) ferrimagnetic domains ferrite hard and soft magnets, magnetic tape (f) metal—semiconductor transition critical temperature NTC thermistor (g) ionic conduction gas sensors and batteries and (h) grain boundary phenomena varistors, boundary layer capacitors, PTC thermistors.

Spinel ferrites, isostmctural with the mineral spinel [1302-67-6] MgAl204, combine interesting soft magnetic properties with a relatively high electrical resistivity. The latter permits low eddy current losses in a-c appHcations, and based on this feature spinel ferrites have largely replaced the iron-based core materials in the r-f range. The main representatives are MnZn-ferrites (frequencies up to about 1 MH2) and NiZn-ferrites (frequencies 1 MHz). 

The soft magnetic spinel ferrites, by far the most important cubic ferrites, were first introduced by Philips under the trade name Ferroxcube (14) and are now widely commercially available under various trade names. The world market for soft magnetic ferrites amounts to about one biUion dollars (1991), about 350 million dollars of which is in the United States. 

Interest is maintained ia these materials because of the combination of mechanical, corrosion, electric, and magnetic properties. However, it is their ferromagnetic properties that lead to the principal appHcation of glassy metals. The soft magnetic properties and remarkably low coercivity offer tremendous opportunities for this appHcation (see Magnetic materials, bulk Magnetic materials, thin film). 

Magnetic Applications. MetaUic glasses ate utilized ia electric transformers and this provides a significant commercial success for these materials. AUoys such as MetGlas 2605 SC, Feg B 5 i3 5 2 prepared ia sheets having superior soft magnetic properties. These alloys can be magnetized... 

The permeabiHty = B jH is important information for soft magnetic materials. The most often quoted values ate the initial permeabiHty and the maximum permeabiHty ]1. These correspond to the initial and maximum slopes of the virgin magnetization curve, respectively (Fig. 1). Because the value of at S/H = 0 needs to be extrapolated from measurements at finite H, the value often is quoted ia commercial catalogues at specific B or H The quoted values usually are relative to the free-space value p.Q. 

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. 

Fig. 2. Magnetization curves of commercial soft magnetic materials.

B. Thomas, Proceedings Conference Soft Magnetic Materials, Cardiff, Wales, 1975, p. 109. 

R. Ball, Soft Magnetic Materials, Heyden and Sun Ltd., London, 1979, handbook of soft magnetic materials. 

C. W. Chen, Magnetism and Metallurgy of Soft Magnetic Materials, North-HoUand, New York, 1977. 

The most commonly used ferrites, the so-called soft ferrites, are used ia soft magnet and low field telecommunication appHcations, low power... 

In contrast, soft magnetic solids and paramagnetic systems with weak anisotropy may be completely polarized by an applied field, that is, the effective field at the Mossbauer nucleus is along the direction of the applied field, whereas the EFG is powder-distributed as in the case of crystallites or molecules. In this case, first-order quadrupole shifts cannot be observed in the magnetic Mossbauer spectra because they are symmetrically smeared out around the unperturbed positions of hyperfine fines, as given by the powder average of EQ mj, d, in (4.51). The result is a symmetric broadening of all hyperfine fines (however, distinct asymmetries arise if the first-order condition is violated). 

Tan, Y.W., Zhuang, Z.B., Peng, Q. and Li, Y.D. (2008) Room-temperature soft magnetic iron oxide nanocrystals ... 

Soft magnetic spinel ferrites, 11 57 Soft oils, in toilet soap making, 22 734 Soft repulsions, 23 94 Soft rot... 

Fe-, Co-, Ni-based alloys of this group are also commercially important for their soft-magnetic properties. 

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