Intrinsic coercivity

Magnet Applications. For magnets of the type FeNdB, a small amount of gallium is effective in improving the intrinsic coercive force (53). It slows the pinning type recoil loop. The thermal stabiUty is increased. The irreversible loss is less than 1.5% under 373 K (1000 h). 

In Figure 13 the relation between the intrinsic coercivity and the particle diameter dis given. The figure is based on a described model (35). The maximum is found around the critical particle diameter. In general the particle diameter and size is not very well defined. For the multidomain particles (d > ) the is smaller than the intrinsic anisotropy field of the particle. Nucleation effects cause a decrease in as the increases. This behavior is... 

Fig. 13. The intrinsic coercivity vs the particle diameter for single- and multidomain particles (35).

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. 

Fig. 18 The saturation magnetization and intrinsic coercivity as a function of calcination temperature for the micro emulsion-derived barium ferrites [145]...

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-... 

Fig. 40. Intrinsic coercive force after sintering at Tsi = 1080 ° C followed by various heat treatments, (a) sintering at 1080 0 C and quenching in oil. (b) same as (a) followed by heating at T, = 900° C for 2 h and quenching in oil. (c) same as (a) followed by heating at 900° C for 2 h and cooling to room temperature, (d) same as (c) followed by heating at T2 for 1 h and quenching in water. (After Tokunaga et al. 1986.)...

Fig. 42. Variation with Dy content of energy product, remanence and intrinsic coercivity of magnets made from calciothermic alloy powders. (After Herget 1987.)...

Fig. 45. Temperature dependence of the residual magnetization (Br). intrinsic coercivity (jHc), and coercivity (fl//c) for hot-pressed (MQ2) and die-upset (MQ3) Nd0.i4(Fe091B0 09 ) 0 86. (After Lee et al.

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. 1. Chronology of magnet development since 1900 Best reported laboratory values for the static energy product and intrinsic coercive force. (After Strnat 1986.)...

Finally, there must be a mechanism for creating a sufficiently high intrinsic coercive force, MHC. What is sufficient depends again on application requirements, but for modem magnet materials it is usually defined as MHC = jBis, the minimum value that permits a close approach to the theoretical energy product limit, (2ttMs)2 = ( BJ2. 

In this chapter Hc is usually used to mean the intrinsic coercive force, mHc or Hc]. The induction coercive force is always abbreviated BHC. 

Fig. 14. Deterioration of the intrinsic coercive force of several RE-TM alloy powders during short-term exposure to air at elevated temperature. (After Stmat 1970.)...

Fig. 29. Dependence of the intrinsic coercive force of sintered and quenched SmCo5 magnets on the temperature of the post-sintering anneal. (After Paladino et al. 1975.)...

Fig. 6.23. Comparison between (a) induction, B, and (b) magnetisation, M, curves, as a function of applied field to illustrate the difference between coercivity, gH,. and intrinsic coercive field, iH-...

---