Q.Write two differences between paramagnetic and ferromagnetic materials.

Diamagnetic substances have atoms with no net moment; an applied field induces a small OPPOSING moment, so they are weakly REPELLED ($\chi$ small, negative, temperature-independent; e.g. copper, bismuth, water). Paramagnetic substances have atoms with a small permanent moment, randomly oriented until a field partially aligns them, so they are weakly ATTRACTED ($\chi$ small, positive, falls as temperature rises -- Curie's law; e.g. aluminium, oxygen). Ferromagnetic substances have permanent atomic moments that align spontaneo …