Relative magnetic permeability of diamagnetic materials is always greater than unity that is

μ_r > 1

Conceptual explanation:

Do you know that permeability word comes from the word “permission”? As it is the natural property of diamagnetic material to weakly attract the lines of force (due to structure of paramagnetic material). Now, if they weakly attract the lines of force or in other words they permit the magnetic lines of force to pass through it but weakly. Therefore, the μ > 1 for paramagnetic materials

Analytical Explanation:

When a specimen of paramagnetic material is placed in a magnetising field, the lines of magnetic force prefer to pass weakly through the specimen. Therefore magnetic induction B inside the paramagnetic material is more than the magnetic intensity H

therefore B/H > 1

As μ = B/H

Therefore μ > 1 for paramagnetic materials

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.