The substance subjected to the magnetic field will perform magnetization and demagnetization by traversing the hysteresis loop. The initial magnetization curve only causes the first magnetization of the material.
This phenomenon causes energy losses from heating because the ferromagnetic material needs considerable electric power to reverse the direction of a magnetic field, to demagnetize it, as in the case of electromagnets.
Each material has a specific hysteresis loop according to the substances that make it up. The choice of the best material depends on the type of application, to minimize losses by magnetic hysteresis
In high-power transformers, a ferro-silicon alloy is used as the core for hysteresis losses to be minimal.
Magnetic circuit is that traversed by the magnetic flux (φ). The toroid is an enclosed solenoid and is given the perfect magnetic circuit designation because it can concentrate all the magnetic flux in its interior without dispersion.
The product N is called magnetomotive force (fmm) and the product represents the work done so that the magnetic flux goes through the circuit, in fact, it is this greatness that causes the flux, behaving as electric voltage (or electromotive force) .