Susceptibility of magnetic material, `chi=I//H` where I is the intensity of magnetisation induced in the material and H is the magnetising force.
Diamagnetism is due to orbital motion of electrons in an atom developing magnetic moments opposite to applied field. Due to it, the resultant magnetic moment of the diamagnetic material is zero. Hence, susceptibility `chi` of diamagnetic material is not much affected by temperature.
Paramagnetism and ferromagnetism is due to alignments of atomic magnetic moments in the direction of the applied field. As temperature is raised, this alignment is disturbed, resulting decrease in susceptibility of both, with increase in temperature.
