Test: Theory Of Ferromagnetism - Mechanical Engineering MCQ

 In a ferromagnetic material, the number of unpaired electrons is more. Most of these spin magnetic moments point in one direction. Hence even in the absence of external field, the magnetic moments align themselves parallel to each other and give rise to magnetic field.

The ferromagnetic materials have permanent dipole moment. So they act as strong magnets.

The ferromagnetic materials exhibit magnetisation even in the absence of external field. This property is called spontaneous magnetisation. Hence ferromagnets exhibit spontaneous magnetisation.

Curie temperature is the temperature at which the magnetic properties of a material changes. When the temperature is greater than curie temperature, ferromagnetic material becomes paramagnetic material.

 In ferromagnetic material there will be large number of unequal electron spins and hence there exists enormous amount of permanent magnetic moment.

The susceptibility is very small and is positive. It is given by, susceptibility = C/(T+θ) for T>T_N. Where, T_N is the Neel temperature.
Initially the susceptibility increases slightly as the temperature increases and beyond a particular temperature, known as Neel temperature, the susceptibility decreases with temperature.

 The ferrites have low hysteresis loss and eddy current loss. Hence they are used in two port devices such as gyrator, circulator and isolator.

Susceptibility = I/H
Intensity of magnetisation I = Susceptibility × H
Intensity of magnetisation = 37A/m

I = Susceptibility × H
I = 1500A/m

 Flux density B = μ₀[H+I] B = 0.012612Wb/m²