Question

For which of the following substances, the magnetic susceptibility is independent of temperature?
(A) diamagnetics only
(B) paramagnetics only
(A) ferromagnetism only
(D) diamagnetism and paramagnetism both

Answer 1

Hint For diamagnetic material, the magnetic susceptibility is independent of temperature. For paramagnetic materials, magnetic susceptibility varies inversely with temperature and for ferromagnetic materials, it is dependent on curie’s temperature of the material.

Complete step by step solution:
Magnetic susceptibility of a material is defined as the tendency of the material to get magnetized in a given external magnetic field. Quantitatively it is defined as:
 \[\chi = \dfrac{M}{H}\]
Where M is the magnetization of the material
H is the measure of externally applied magnetic field
When a paramagnetic substance is heated, its electrons start to vibrate faster. This vibration is due to the external energy gained by heating of the material. This vibration will thus further affect the alignment of magnetic dipoles and further reduces its magnetic susceptibility. For a paramagnetic substance, it is inversely proportional to the absolute temperature.
For a ferromagnetic substance, the magnetic susceptibility is very high. This high value also tends to show up a large deviation when the temperature is applied to the substance. Magnetic susceptibility of the substance is inversely proportional to the difference of absolute temperature and curie’s temperature of the substance.
 \[\chi {\text{ }} \propto {\text{ }}\dfrac{1}{{{T_c} - T}}\]
Diamagnetic substances have a small negative value as magnetic susceptibility. The overall change in magnetic susceptibility is very negligible with an increase in temperature.

Note: The paramagnetic substance has a small but positive magnetic susceptibility. Ferromagnetic substances have a very large value and diamagnetic substances have a very small negative susceptibility.
Ferromagnetic materials behave as a paramagnetic above a certain temperature called curie temperature.