Coercivity

The progress in the twentieth century which has spawned such a range of magnetic applications can be summarized in threewords – mastery of coercivity. No new ferromagnetic material has been discovered with a magnetization greater than that of ‘permendur’, Fe65Co35, forwhich Ms = 1950 kA m⁻¹, but coercivity which barely spanned two orders of magnitude in 1900, from the softest soft iron to the hardest magnet steel, now ranges over eight orders of

Figure 1.1: Progress in expanding the range of coercivity of magnetic materials during the twentieth century.

magnitude, from less than 0.1 A m⁻¹ to more than 10 MA m⁻¹, as shown in Fig. 1.1.