# Rayleigh's Law of Magnetization

## Rayleigh’s Law of Magnetization

the dependence, established by Lord Rayleigh in 1887, of the magnetization J (or magnetic induction B) of ferromagnetics on magnetic field strength H in weak fields—that is, where the strength of the field acting on the specimen is much smaller than the coercive force HC

Rayleigh’s law of magnetization can be expressed by the following two equations: (1) for the curve of initial magnetization, J = KREVH ± RH2 (SEEMAGNETIZATION CURVE), where Krev is the reversible magnetic susceptibility, which characterizes the reversible linear part of the process, and R is Rayleigh’s constant, which characterizes irreversible nonlinear magnetization processes; (2) for the ascending and descending branches of the hysteresis loops, ǀΔJǀ = KREVǀΔHǀ + RǀΔHǀ2/2, where ǀΔJǀ and ǀΔHǀ are the absolute values of the increments to J and H.

Rayleigh’s law is satisfied not only near the demagnetized state (J = 0, H = 0), but also for other initial values of J or B, as long as the value of H and the variation AH in this value are small compared with HC (H, AH ≪ HC). The parameters KREV and R may, of course, vary. Near the demagnetized state, KREV coincides with the reversible initial magnetic susceptibility κa and is due to reversible shifts in the domain boundaries (see MAGNETIZATION). If initial J ≠ 0 and H ≠ 0, then KrevΦ κa. Even in this case, however, KREV is determined by reversible processes of the displacement of domain boundaries. The parameter R characterizes irreversible shifts of domain boundaries. The range of applicability of Rayleigh’s law for different ferromagnetics may vary from a few millioersteds (ferrites) to a few oersteds (perminvars).

### REFERENCE

Vonsovskii, S. V. Magnetizm. Moscow, 1971.

O. V. ROSNITSKII

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