Magnetization surfaces in (M, H, Ṁ) space

Thermal activation of magnetization processes leads to time dependence of intensity of magnetization, M. The description of the equation of state of a magnetized material thus requires the specification of the time rate of change of magnetization, Ṁ, in addition to M and the magnetic field, H. The magnetic state can be derived from a constitutive equation, the solutions of which are represented by surfaces in three-dimensional (M, H, Ṁ) space. Magnetization behaviour, subject to such conditions as constant H, constant Ḣ and constant Ṁ, is given by trajectories on the (M, H, Ṁ) surfaces. A computer generated (M, H, Ṁ) surface derived from experimental data on sintered Pr₁₅Fe₇₇B₈ has been calculated. The variations of M vs. H under conditions of constant Ṁ and of constant Ḣ are derived from trajectories on this surface and they are compared with direct experimental data.