Magnetization Curve

a graph, table, or formula that shows the dependence of the magnetization J or magnetic induction B on the magnetic-field intensity H. If the function J(H) is known, then the induction curve B(H) can be constructed for the same substance, since the simultaneous values of B, J, and H that refer to the same volume element of the substance are related by the equation B = H + 4∏J (in the centimeter-gram-second system of units) or B = μ₀ (H + J) (in SI units, where μ₀ is the magnetic constant).

The magnetization curves for magnetic materials depend not only on the physical properties of the materials and the external conditions but also on the sequence of passage through various magnetic states. In this connection, we consider several types of magnetization curves: (1) curves of initial magnetization (Figure

Figure 1. Curves of initial magnetization of permalloys: (1) chromium permalloy, (2) molybdenum permalloy, (3) permalloy with 75.8 percent Ni and the remainder Fe, (4) permalloy with 45 percent Ni and the remainder Fe

1), which are the sequences of values of J or B that a substance assumes as H increases monotonically from an initial state with B = H = J = 0 (in this case, H does not change direction); (2) cyclic magnetic-reversal curves (or static hysteresis loops), which are the functional forms of B(H) or J(H) that are obtained after repeated passage through a certain range of values of H in the forward and reverse directions (Figure 2); and (3) normal magnetization (or commutation) curves, which are the loci of the tips of the symmetric loops of magnetic reversal (Figure 2).

Figure 2. Family of symmetric hysteresis loops (2) and the normal magnetization curve (1) for molybdenum permalloy (79 percent Ni, 4 percent Mo, 0.2 percent Mn, the remainder Fe)

Magnetization curves enable us to determine the characteristics of magnetic materials, for example, residual magnetization, coercive force H_c, and magnetic permeability. These characteristics are used in design calculations for the magnetic circuits of electromagnets, magnetic starters, relays, and other electrotechnical devices and instruments.