Maximum energy product

H, for which J = 0, is the intrinsic coercivity whereas the usual coercivity, for which S = 0, is denoted by H or H. For permanent magnets, the value (BH), the maximum energy product, is an important measure of quaHty. The value (BH), iadicated ia the secoad quadrant of Figure 1, represents the poiat of maximum efficieacy where a givea amouat of magnetic flux is produced by the smallest amouat of material. 

Magnet Type Maximum Energy Product kJ /m Remanence Br T Coercivity bHc kA/m... 

The importance of improved magneiie alloys is sometimes underestimated. Magnets are used widely in telecommunications and in scores of electrical and electronic instruments and appliances, and it has been estimated thal the demand lor permanent magnets has increased by a factor of three since 197(1. Chromium-cohall-iron alloys have increased markedly in application. It is interesting to note thal these magnets have essentially about Uve same coercive force and maximum energy product as Alnico 5. but with only half the cohall content. 

The operating state of a permanent magnet lies in the second quadrant of a B-H hysteresis loop since the magnet is always subject to its own demagnetizing field. Apart from its coercivity and remanence, a permanent magnet material is rated by its maximum energy product ... 

A guide to the quality of hard ferrites can be obtained from the maximum energy product (B which can... 

A quality guide for permanent magnets is the maximum energy product (B Hlm. ... 

The maximum energy product is not, however, the only criterion that can be used to specify the quality of a permanent magnet material whose usefulness is mainly limited to static applications. Of importance in many applications is the magnitude... 

The effect of a variable Nd and B concentration was extensively investigated by Sagawa et al. (1984a). They found that the remanence Br shows a comparatively small concentration dependence. By contrast, the intrinsic coercive force jHc depends strongly on the Fe concentration. The marked decrease of the maximum energy product ( BZf)max observed for high Fe concentrations is mainly due to the rapid decrease of jHc in this concentration range. This behaviour may be under-... 

In section 3.2 it was mentioned that, in addition to a large maximum energy product, a high intrinsic coercive force jHc is needed in some applications. Moreover, the maximum energy product (BH)max itself depends on the coercive force and may become lower than the theoretical limit (Z 77)max = Bt bHc = Js2/4/jl0 if bHc falls appreciably below the value Js/n0. It is desirable therefore to have some understanding of the mechanisms that determine the ultimate magnitude of the coercive force in permanent magnets. 

Fig. 4.57. Schematic determination of the maximum energy product from the demagnetisation curve.

If quenched from the y-phase state, the alloy can be deformed. By a judicious choice of annealing temperatures in the range of 555 to 750 °C the maximum energy product as a function of alloy composition, as shown in Fig. 4.3-57, may be obtained. This annealing treatment is associated with a drastic increase in hardness. 

High coercivities High remanence Maximum energy product (BH) High Curie temperature... 

Name Al Composition, Weight Percent Ni Co Cu Other Remanence, Br,G Coercive Force, H, 0 Maximum Energy Product, (BEf)max. G-O XlO" ... 

Summarizing it must be stated, however, that at present the problem of a Nd-Fe-B based permanent magnet with sufficient high coercivity to reach the maximum energy product corresponding to... 

The composition dependence of the magnetic properties of Ndj (Feo, 95 0. 05)jr amorphous alloys is plotted in fig. 28 (Croat et al. 1984b). The maximum energy product for this isotropic magnet is obtained for x = 0.87, namely =... 

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