a
Magnetic susceptibility \(\chi \) is related to permeability \(μ\) by \(μ = 1+ 4\pi \chi _m\) . For diamagnetic substances \(\chi _m\) is negative and \(μ< 1\) (negative). Ideal diamagnet should expel all magnetic field lines inside it i.e. \(\chi _m < 0\) or \(\chi _m = -\,1\)