Susceptibility comes from the word “susceptible” means the easily affected. As I have discussed earlier that lines of force are expelled or repelled from diamagnetic materials, when these materials are placed in external magnetic field. It means diamagnetic materials are not effected by the field. Therefore the susceptibility of diamagnetic materials is negative.
As we have discussed in the earlier articles, that relative permeability of diamagnetic materials is lesser than 1 and also there is a relation between relative permeability (μr)and susceptibility (χ):
μr = 1 + χ
where is μr
or χ = μr – 1
and μr is less than 1
therefore, χ is negative
Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0. In case of any question, you can put your question in the comment section.