Question

The susceptibility of a certain magnetic material is 400. Find the class of the magnetic material.
A) Diamagnetic
B) Paramagnetic
C) Ferromagnetic
D) Ferroelectric

Answer 1

Hint: The susceptibility of a material describes how the material behaves when it is placed in an external magnetic field. If the material repels the magnetic field, then the susceptibility of that material would be negative or less than zero. If the material attracts the magnetic field, then the susceptibility of that material would be greater than zero or positive.

Complete step by step answer:
There are mainly three kinds of magnetic materials.
There are materials that repel the external magnetic field, materials that weakly attract the magnetic field, and finally, we have materials that strongly attract the magnetic field.
The materials that repel the field are called diamagnetic and those that get weakly attracted are called paramagnetic.
The materials which get strongly attracted to the external field are called ferromagnetic materials. Now for these materials, the magnetization will persist even if the field is removed.
Since the susceptibility of a material essentially refers to the measure of magnetization of material when placed in an external magnetic field, ferromagnetic materials must have very large values for susceptibility.
i.e., ${\chi _{ferro}} > > 1$

The susceptibility of the given material is 400 which is a very large value. So the class of the given material will be ferromagnetic. Hence the correct option is (C).

Additional information:
In the absence of an external field, the magnetic moments of each atom in a ferromagnetic material will align themselves in a common direction and thus form domains. Each domain will have a different direction so that the bulk magnetization is zero. Now when this material is placed in an external field, all the domains will orient themselves in the direction of the external field. Thus the material gets strongly magnetized.

Note:
Since a diamagnetic material repels the applied field, its susceptibility will be less than one i.e., ${\chi _{dia}} < 1$. The paramagnetic material, however, gets attracted to the magnetic field, and thus the susceptibility of the material will be greater than one but as it only gets weakly magnetized, its susceptibility will have small positive values i.e., ${\chi _{para}} > 1$.