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Asked in GSEB Board March 2020 (old course) · Dia, para and ferromagnetism
Idea: inside a material ⃗B=μ₀(1+χₘ)⃗H, so the relative permeability is μᵣ=1+χₘ.
A superconductor expels the field completely (the Meissner effect), so ⃗B=0 in its interior.
With ⃗H eq0 this forces 1+χₘ=0, that is χₘ=-1.
Then μᵣ=1+χₘ=1-1=0.
So a superconductor has χₘ=-1 and μᵣ=0: the ideal diamagnet, the extreme case of the diamagnetic range -1≤χₘ<0.
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