The reason a soft ferromagnetic material loses its magnetism when the external field is removed is:
**Permanent magnet requirement** is high retentivity to maintain field and high coercivity to resist demagnetization. Ability to retain magnetism after field removal is property of hard ferromagnets, related to domain wall pinning and anisotropy. Soft ferromagnetic materials have low coercivity and do not retain significant magnetization after the external field is removed. Their domains, which align strongly in the presence of a field, return to a random orientation due to minimal internal resistance, unlike hard ferromagnets. Substituting values gives Its domains randomize without the field, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.
Ref: NCERT > Physics Book > Magnetism and Matter > Hysteresis, Retentivity, Coercivity and Permanent Magnets