A material placed in a magnetic field reduces the field inside it slightly due to:
**Magnetic dipole moment** quantifies strength and orientation of magnet, m = 2l × q_m where q_m pole strength. Field line concept visualizes B, with closed nature reflecting absence of magnetic monopoles, explaining non-intersection and continuity. Diamagnetic materials reduce the magnetic field inside them slightly because an external field induces weak currents that create an opposing magnetic moment, resulting in a small negative susceptibility and a minor field reduction. Substituting values gives Induced opposing magnetic moments, which matches expected magnitude for this magnetic config
Ref: NCERT > Physics Book > Magnetism and Matter > Magnetic Field Lines, Bar Magnet and Dipole Moment